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. In chemistry, a nonmetal (or non-metal) is a that mostly lacks attributes. Physically, nonmetals tend to have relatively low melting and boiling points, and densities, are mostly brittle if solid, and are usually poor conductors of heat and electricity; chemically, they tend to have relatively high ionization energy, electron affinity, and values, and gain or share electrons when they react with other elements or compounds. Seventeen elements are generally classified as nonmetals; most are gases (hydrogen, helium, nitrogen, oxygen, fluorine, neon, chlorine, argon, krypton, xenon and radon); one is a liquid (bromine), and a few are solids (carbon, phosphorus, sulfur, selenium, and iodine). Such as boron, silicon and germanium are sometimes counted as nonmetals. The nonmetals are divided into two categories reflecting their relative propensity to form chemical compounds namely reactive nonmetals and noble gases.

The reactive nonmetals vary in nonmetallic character. The less electronegative of them, such as carbon and sulfur, mostly have weak to moderately strong nonmetallic properties and tend to form covalent compounds with metals. The more electronegative of the reactive nonmetals, such as oxygen and fluorine are characterised by stronger nonmetallic properties and a tendency to form predominantly ionic compounds with metals. The noble gases are distinguished by their great reluctance to form compounds with other elements.

The distinction between categories is not absolute. Boundary overlaps, including with the metalloids, occur as outlying elements in each category show (or begin to show) less-distinct, hybrid-like or atypical properties. Although five times more elements are metals than nonmetals, two of the nonmetals—hydrogen and helium—make up over 99 per cent of the observable Universe, and one—oxygen—makes up close to half of the Earth's crust, oceans and atmosphere. Living organisms are composed almost entirely of nonmetals, and nonmetals form many more compounds than metals.

There is no rigorous definition of a nonmetal. Broadly, any element lacking a preponderance of metallic properties can be regarded as a nonmetal. The elements generally classified as nonmetals include one element in group 1 ; one in ; two in ( and ); three in (, and ); most of (, and ); and all of (with the possible exception of ). As there is no widely agreed definition of a nonmetal, elements in the periodic table vicinity of where the metals meet the nonmetals are inconsistently classified by different authors. Elements sometimes also classified as nonmetals are the (B), (Si), (Ge), (As), (Sb), (Te), and (At). The nonmetal selenium (Se) is sometimes instead classified as a metalloid, particularly in.

Properties. ” JJ Zuckerman and FC Nachod In Steudel's (1977, preface) Nonmetals show more variability in their properties than do metals.

These properties are largely determined by the interatomic bonding strengths and molecular structures of the nonmetals involved, both of which are subject to variation as the number of valence electrons in each nonmetal varies. Metals, in contrast, have more homogenous structures and their properties are more easily reconciled. Physically, they largely exist as diatomic or monatomic gases, with the remainder having more substantial (open-packed) forms, unlike metals, which are nearly all solid and close-packed. If solid, they have a appearance (with the exception of sulfur) and are mostly, as opposed to metals, which are, and generally or; they usually have lower than metals; are mostly poorer conductors of and; and tend to have significantly lower and than those of metals. Scatter plot of electronegativity values and standard electrode potentials of chemically active nonmetallic elements, showing a rough correlation between the two properties. The higher the standard electrode potential, the greater is the capacity to act as an. The chart shows that oxygen and the nonmetallic halogens are the strongest oxidising agents and that, for the most part, the elements commonly recognised as metalloids are the weakest.

The electrode potentials are for the reduction of the elements to monatomic anions (X→X −; X = F, Cl, Br, I, or H) or to their protonated forms (for example, O 2→H 2O; N 2→NH 3. Hydrogen and nitrogen have anomalous standard electrode potentials due to their reluctance to form anions. A broad progression in nonmetallic character is seen, with the metalloids in the lower left, and oxygen and the nonmetallic halogens in the upper right. Trend lines are shown with and without the anomalous hydrogen and nitrogen values.

The R 2 values show how close each trend line fits its data points. Values range from 0.0 (indicating no fit) and 1.0 (a very good fit). Chemically the nonmetals mostly have high, high electron affinities (nitrogen and the noble gases have negative electron affinities) and high values noting that, in general, the higher an element's ionisation energy, electron affinity, and electronegativity, the more nonmetallic that element is.

Nonmetals (including – to a limited extent – xenon and probably radon) usually exist as anions or oxyanions in aqueous solution; they generally form ionic or covalent compounds when combined with metals (unlike metals, which mostly form alloys with other metals); and have whereas the common oxides of nearly all metals are. Complicating the chemistry of the nonmetals is the first row anomaly seen particularly in hydrogen, (boron), carbon, nitrogen, oxygen and fluorine; and the alternation effect seen in (arsenic), selenium and bromine. The first row anomaly largely arises from the electron configurations of the elements concerned. Hydrogen is noted for the different ways it forms bonds. It most commonly forms covalent bonds. It can lose its single valence electron in aqueous solution, leaving behind a bare proton with tremendous polarising power.

This subsequently attaches itself to the lone electron pair of an oxygen atom in a water molecule, thereby forming the basis of acid-base chemistry. Under certain conditions a hydrogen atom in a molecule can form a second, weaker, bond with an atom or group of atoms in another molecule.

Such bonding, 'helps give snowflakes their hexagonal symmetry, binds DNA into a double helix; shapes the three-dimensional forms of proteins; and even raises water’s boiling point high enough to make a decent cup of tea.' From (boron) to neon, since the 2p subshell has no inner analogue and experiences no electron repulsion effects it consequently has a relatively small radius, unlike the 3p, 4p and 5p subshells of heavier elements (a similar effect is seen in the 1s elements, hydrogen and helium). Ionisation energies and electronegativities among these elements are consequently higher than would otherwise be expected, having regard to periodic trends.

The small atomic radii of carbon, nitrogen, and oxygen facilitates the formation of triple or double bonds. The larger atomic radii, which enable higher coordination numbers, and lower electronegativities, which better tolerate higher positive charges, of the heavier group 15–18 nonmetals means they are able to exhibit valences other than the lowest for their group (that is, 3, 2, 1, or 0) for example in PCl 5, SF 6, IF 7, and XeF 2. Period four elements immediately after the first row of the transition metals, such as selenium and bromine, have unusually small atomic radii because the 3d electrons are not effective at shielding the increased nuclear charge, and smaller atomic size correlates with higher electronegativity.

Categories Immediately to the left of most nonmetals on the periodic table are metalloids such as boron, silicon, and germanium, which generally behave chemically like nonmetals, and are included here for comparative purposes. In this sense they can be regarded as the most metallic of nonmetallic elements. Based on shared attributes, the nonmetals can be divided into the two categories of reactive nonmetal, and noble gas. The metalloids and the two nonmetal categories then span a progression in chemical nature from weakly nonmetallic, to moderately nonmetallic, to strongly nonmetallic (oxygen and the four nonmetallic halogens), to almost inert. Analogous categories occur among the metals in the form of the weakly metallic (the ), the moderately metallic (most of the ), the strongly metallic (the and, and the and ), and the relatively inert (the ). As with categorisation schemes generally, there is some variation and overlapping of properties within and across each category.

One or more of the metalloids are sometimes classified as nonmetals. Among the reactive nonmetals, carbon, phosphorus, selenium, and iodine—which border the metalloids—show some metallic character, as does hydrogen. Among the noble gases, radon is the most metallic and begins to show some cationic behaviour, which is unusual for a nonmetal. Metalloid. Main article: The seven metalloids are boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te), and astatine (At).

On a standard periodic table, they occupy a diagonal area in the p-block extending from boron at the upper left to astatine at lower right, along the shown on some periodic tables. They are called metalloids mainly in light of their physical resemblance to metals. While they each have a metallic appearance, they are brittle and only fair conductors of electricity. Boron, silicon, germanium, tellurium are semiconductors. Arsenic and antimony have the electronic band structures of semimetals although both have less stable semiconducting allotropes. Astatine has been predicted to have a metallic crystalline structure.

Electronegativity values of metalloids and nonmetals Noble gases H 2.2 Reactive nonmetals He (5.5) B 2.04 C 2.55 N 3.04 O 3.44 F 3.98 Ne (4.84) Si 1.9 P 2.19 S 2.58 Cl 3.16 Ar (3.2) Ge 2.01 As 2.18 Se 2.55 Br 2.96 Kr (2.94) Sb 2.05 Te 2.1 I 2.66 Xe (2.4) Metalloids At 2.2 Rn (2.06) Electronegativity (EN) gives some indication of nonmetallic character. The metalloids have uniformly moderate values (1.8–2.2). Among the reactive nonmetals, hydrogen (2.2) and phosphorus (2.19) have moderate values but they each have higher ionisation energies than the metalloids, and are very rarely classed as such. Oxygen and the nonmetallic halogens have uniformly high EN values; nitrogen has a high EN but a marginally negative electron affinity that makes it a reluctant anion former.

The noble gases have some of the highest ENs but their complete valence shells and sizeably negative electron affinities render them chemically inert to a large degree. Chemically the metalloids generally behave like (weak) nonmetals. They have moderate ionisation energies, low to high electron affinities, moderate electronegativity values, are poor to moderately strong oxidising agents, and demonstrate a tendency to form alloys with metals. Reactive nonmetal. The reactive nonmetals have a diverse range of individual physical and chemical properties. In periodic table terms they largely occupy a position between the weakly nonmetallic metalloids to the left and the noble gases to the right. Physically, four are solids, one is a liquid (bromine), and six are gases.

Of the solids, carbon, selenium, and iodine are metallic-looking, whereas sulfur has a pale-yellow appearance. Ordinary white phosphorus has a yellowish-white appearance but the black allotrope, which is the most stable form of phosphorus, has a metallic-looking appearance.

Bromine is reddish-brown in colour. Of the gases, fluorine and chlorine are coloured pale yellow, and yellowish green. Electrically, most are insulators whereas carbon is a semimetal and black phosphorus, selenium, and iodine are semiconductors. Chemically, they tend to have moderate to high ionisation energies, electron affinities, and electronegativity values, and be relatively strong oxidising agents.

Collectively, the highest values of these properties are found among oxygen and the nonmetallic halogens. Manifestations of this status include oxygen's major association with the ubiquitous processes of corrosion and combustion, and the intrinsically corrosive nature of the nonmetallic halogens. All five of these nonmetals exhibit a tendency to form predominately ionic compounds with metals whereas the remaining nonmetals tend to form predominately covalent compounds with metals. Noble gas. Main article: Six nonmetals are categorised as noble gases:, and the radioactive. In periodic table terms they occupy the outermost right column.

They are called noble gases in light of their characteristically very low. They have very similar properties, all being colorless, odourless, and nonflammable.

With their closed valence shells the noble gases have feeble of attraction resulting in very low melting and boiling points. That is why they are all gases under, even those with larger than many normally solid elements. Chemically, the noble gases have relatively high ionisation energies, negative electron affinities, and relatively high electronegativities. Compounds of the noble gases number less than half a thousand, with most of these occurring via oxygen or fluorine combining with either krypton, xenon or radon. The status of the period 7 congener of the noble gases, is not known—it may or may not be a noble gas. It was originally predicted to be a noble gas but may instead be a fairly reactive solid with an anomalously low first ionisation potential, and a positive electron affinity, due to. On the other hand, if relativistic effects peak in period 7 at element 112, oganesson may turn out to be a noble gas after all, albeit more reactive than either xenon or radon.

While oganesson could be expected to be the most metallic of the group 18 elements, credible predictions on its status as either a metal or a nonmetal (or a metalloid) appear to be absent. Comparison of properties Characteristic and other properties of metalloids, reactive nonmetals, and noble gases are summarized in the following table. Metalloids have been included in light of their generally nonmetallic chemistry. Physical properties are listed in loose order of ease of determination; chemical properties run from general to specific, and then to descriptive. Hydrogen in an electrical discharge tube Hydrogen is a colourless, odourless, and comparatively unreactive diatomic gas with a density of 0.08988 × 10 −3 g/cm 3 and is about 14 times lighter than air. It condenses to a colourless liquid −252.879 °C and freezes into an ice- or snow-like solid at −259.16 °C.

The solid form has a hexagonal crystalline structure and is soft and easily crushed. Hydrogen is an insulator in all of its forms.

It has a high ionisation energy (1312.0 kJ/mol), moderate electron affinity (73 kJ/mol), and moderate electronegativity (2.2). Hydrogen is a poor oxidising agent (H 2 + 2 e − → 2H – = –2.25 V at pH 0).

Its chemistry, most of which is based around its tendency to acquire the electron configuration of the noble gas helium, is largely covalent in nature, noting it can form ionic hydrides with highly electropositive metals, and alloy-like hydrides with some transition metals. The common oxide of hydrogen is a neutral oxide.

Group 13. Boron Boron is a lustrous, barely reactive solid with a density 2.34 g/cm 3 (cf. Aluminium 2.70), and is hard ( 9.3) and brittle. It melts at 2076 °C (cf. Steel 1370 °C) and boils at 3927 °C. Boron has a complex rhombohedral crystalline structure (CN 5+).

It is a semiconductor with a band gap of about 1.56 eV. Boron has a moderate ionisation energy (800.6 kJ/mol), low electron affinity (27 kJ/mol), and moderate electronegativity (2.04). Being a metalloid, most of its chemistry is nonmetallic in nature. Boron is a poor oxidizing agent (B 12 + 3 e → BH 3 = –0.15 V at pH 0). While it bonds covalently in nearly all of its compounds, it can form intermetallic compounds and alloys with transition metals of the composition M nB, if n  2. The common oxide of boron (B 2O 3) is weakly acidic. Group 14.

Carbon, as graphite Carbon (as graphite, its most thermodynamically stable form) is a lustrous and comparatively unreactive solid with a density of 2.267 g/cm 3, and is soft (MH 0.5) and brittle. It has sublimes to vapour at 3642 C°. Carbon has a hexagonal crystalline structure (CN 3). It is a semimetal in the direction of its planes, with an electrical conductivity exceeding that of some metals, and behaves as a semiconductor in the direction perpendicular to its planes. It has a high ionisation energy (1086.5 kJ/mol), moderate electron affinity (122 kJ/mol), and high electronegativity (2.55). Carbon is a poor oxidising agent (C + 4 e − → CH 4 = 0.13 V at pH 0).

Its chemistry is largely covalent in nature, noting it can form salt-like carbides with highly electropositive metals. The common oxide of carbon is a medium-strength acidic oxide. Silicon has a blue-grey metallic lustre. Silicon is a metallic-looking relatively unreactive solid with a density of 2.3290 g/cm 3, and is hard (MH 6.5) and brittle. It melts at 1414 °C (cf. Steel 1370 °C) and boils at 3265 °C. Silicon has a diamond cubic structure (CN 4).

It is a semiconductor with a band gap of about 1.11 eV. Silicon has a moderate ionisation energy (786.5 kJ/mol), moderate electron affinity (134 kJ/mol), and moderate electronegativity (1.9). It is a poor oxidising agent (Si + 4 e → Si 4 = –0.147 at pH 0). As a metalloid the chemistry of silicon is largely covalent in nature, noting it can form alloys with metals such as iron and copper. The common oxide of silicon is weakly acidic. Germanium Germanium is a shiny, mostly unreactive grey-white solid with a density of 5.323 g/cm 3 (about two-thirds that of iron), and is hard (MH 6.0) and brittle.

It melts at 938.25 °C (cf. Silver 961.78 °C) and boils at 2833 °C. Germanium has a diamond cubic structure (CN 4). It is a semiconductor with a band gap of about 0.67 eV. Germanium has a moderate ionisation energy (762 kJ/mol), moderate electron affinity (119 kJ/mol), and moderate electronegativity (2.01). It is a poor oxidising agent (Ge + 4 e → GeH 4 = –0.294 at pH 0). As a metalloid the chemistry of germanium is largely covalent in nature, noting it can form alloys with metals such as aluminium and gold.

Most alloys of germanium with metals lack metallic or semimetallic conductivity. The common oxide of germanium is amphoteric. Liquid nitrogen Nitrogen is a colourless, odourless, and relatively inert diatomic gas with a density of 1.251 × 10 −3 g/cm 3 (marginally heavier than air). It condenses to a colourless liquid at −195.795 °C and freezes into an ice- or snow-like solid −210.00 °C. The solid form (density 0.85 g/cm −3; cf. Lithium 0.534) has a hexagonal crystalline structure and is soft and easily crushed. Nitrogen is an insulator in all of its forms.

It has a high ionisation energy (1402.3 kJ/mol), low electron affinity (–6.75 kJ/mol), and high electronegativity (3.04). The latter property manifests in the capacity of nitrogen to form usually strong hydrogen bonds, and its preference for forming complexes with metals having low electronegativities, small cationic radii, and often high charges (+3 or more). Nitrogen is a poor oxidising agent (N 2 + 6 e − → 2NH 3 = −0.057 V at pH 0). Only when it is in a positive oxidation state, that is, in combination with oxygen or fluorine, are its compounds good oxidising agents, for example, 2NO 3 − → N 2 = 1.25 V.

Its chemistry is largely covalent in nature; anion formation is energetically unfavourable owing to strong inter electron repulsions associated with having three unpaired electrons in its outer valence shell, hence its negative electron affinity. The common oxide of nitrogen is weakly acidic. Many compounds of nitrogen are less stable than diatomic nitrogen, so nitrogen atoms in compounds seek to recombine if possible and release energy and nitrogen gas in the process, which can be leveraged for explosive purposes.

Phosphorus, as black phosphorus Phosphorus in its most thermodynamically stable black form, is a lustrous and comparatively unreactive solid with a density of 2.69 g/cm 3, and is soft (MH 2.0) and has a flaky comportment. It sublimes at 620 °C. Black phosphorus has an orthorhombic crystalline structure (CN 3). It is a semiconductor with a band gap of 0.3 eV.

It has a high ionisation energy (1086.5 kJ/mol), moderate electron affinity (72 kJ/mol), and moderate electronegativity (2.19). In comparison to nitrogen, phosphorus usually forms weak hydrogen bonds, and prefers to form complexes with metals having high electronegativities, large cationic radii, and often low charges (usually +1 or +2.

Phosphorus is a poor oxidising agent (P 4 + 3 e − → PH 3 – = −0.046 V at pH 0 for the white form, −0.088 V for the red). Its chemistry is largely covalent in nature, noting it can form salt-like phosphides with highly electropositive metals. Compared to nitrogen, electrons have more space on phosphorus, which lowers their mutual repulsion and results in anion formation requiring less energy. The common oxide of phosphorus is a medium-strength acidic oxide.

White phosphorus, stored under water to prevent its oxidation When assessing periodicity in the properties of the elements it needs to be borne in mind that the quoted properties of phosphorus tend to be those of its least stable white form rather than, as is the case with all other elements, the most stable form. White phosphorus is the most common, industrially important, and easily reproducible allotrope. For those reasons it is the standard state of the element. Paradoxically, it is also thermodynamically the least stable, as well as the most volatile and reactive form. It gradually changes to red phosphorus. This transformation is accelerated by light and heat, and samples of white phosphorus almost always contain some red phosphorus and, accordingly, appear yellow.

For this reason, white phosphorus that is aged or otherwise impure is also called yellow phosphorus. When exposed to oxygen, white phosphorus glows in the dark with a very faint tinge of green and blue. It is highly flammable and pyrophoric (self-igniting) upon contact with air.

Asvab Study Guide

White phosphorus has a density of 1.823 g/cm 3, is soft (MH 0.5) as wax, pliable and can be cut with a knife. It melts at 44.15 °C and, if heated rapidly, boils at 280.5 °C; it otherwise remains solid and transforms to violet phosphorus at 550 °C. It has a body-centred cubic structure, analogous to that of manganese, with unit cell comprising 58 P 4 molecules. It is an insulator with a band gap of about 3.7 eV. Arsenic, sealed in a container to prevent tarnishing Arsenic is a grey, metallic looking solid which is stable in dry air but develops a golden bronze patina in moist air, which blackens on further exposure.

It has a density of 5.727 g/cm 3, and is brittle and moderately hard (MH 3.5; more than aluminium; less than iron). Arsenic sublimes at 615 °C.

It has a rhombohedral polyatomic crystalline structure (CN 3). Arsenic is a semimetal, with an electrical conductivity of around 3.9 × 10 4 S.cm −1 and a band overlap of 0.5 eV. It has a moderate ionisation energy (947 kJ/mol), moderate electron affinity (79 kJ/mol), and moderate electronegativity (2.18).

Arsenic is a poor oxidising agent (As + 3e → AsH 3 = –0.22 at pH 0). As a metalloid, its chemistry is largely covalent in nature, noting it can form brittle alloys with metals, and has an extensive organometallic chemistry. Most alloys of arsenic with metals lack metallic or semimetallic conductivity. The common oxide of arsenic (As 2O 3) is acidic but weakly amphoteric. Antimony, showing its brilliant lustre Antimony is a silver-white solid with a blue tint and a brilliant lustre. It is stable in air and moisture at room temperature.

Antimony has a density of 6.697 g/cm 3, and is moderately hard (MH 3.0; about the same as copper). It has a rhombohedral crystalline structure (CN 3). Antimony melts at 630.63 °C and boils at 1635 °C.

It is a semimetal, with an electrical conductivity of around 3.1 × 10 4 S.cm −1 and a band overlap of 0.16 eV. Antimony has a moderate ionisation energy (834 kJ/mol), moderate electron affinity (101 kJ/mol), and moderate electronegativity (2.05). It is a poor oxidising agent (Sb + 3e → SbH 3 = –0.51 at pH 0). As a metalloid, its chemistry is largely covalent in nature, noting it can form alloys with one or more metals such as aluminium, iron, copper, zinc, tin, lead and bismuth, and has an extensive organometallic chemistry.

Most alloys of antimony with metals have metallic or semimetallic conductivity. The common oxide of antimony (Sb 2O 3) is amphoteric. ” MD Joesten, L Hogg, and ME Castellion In The world of chemistry (2007, p. 217) Oxygen is a colourless, odourless, and unpredictably reactive diatomic gas with a gaseous density of 1.429 × 10 −3 g/cm 3 (marginally heavier than air). It is generally unreactive at room temperature. Thus, sodium metal will 'retain its metallic lustre for days in the presence of absolutely dry air and can even be melted (m.p. 97.82 °C) in the presence of dry oxygen without igniting'.

On the other hand, oxygen can react with many inorganic and organic compounds either spontaneously or under the right conditions, (such as a flame or a spark) or ultra-violet light?. It condenses to pale blue liquid −182.962 °C and freezes into a light blue solid at −218.79 °C. The solid form (density 0.0763 g/cm −3) has a cubic crystalline structure and is soft and easily crushed. Oxygen is an insulator in all of its forms. It has a high ionisation energy (1313.9 kJ/mol), high electron affinity (141 kJ/mol), and high electronegativity (3.44). Oxygen is a strong oxidising agent (O 2 + 4 e → 2H 2O = 1.23 V at pH 0).

Metal oxides are largely ionic in nature. Sulfur Sulfur is a bright-yellow moderately reactive solid. It has a density of 2.07 g/cm 3 and is soft (MH 2.0) and brittle. It melts to a light yellow liquid 95.3 °C and boils at 444.6 °C.

Sulfur has an abundance on earth one-tenth that of oxygen. It has an orthorhombic polyatomic (CN 2) crystalline structure, and is brittle. Sulfur is an insulator with a band gap of 2.6 eV, and a photoconductor meaning its electrical conductivity increases a million-fold when illuminated. Sulfur has a moderate ionisation energy (999.6 kJ/mol), moderate electron affinity (200 kJ/mol), and high electronegativity (2.58).

It is a poor oxidising agent (S 8 + 2 e − → H 2S = 0.14 V at pH 0). The chemistry of sulfur is largely covalent in nature, noting it can form ionic sulfides with highly electropositive metals. The common oxide of sulfur is strongly acidic. Selenium Selenium is a metallic-looking, moderately reactive solid with a density of 4.81 g/cm 3 and is soft (MH 2.0) and brittle. It melts at 221 °C to a black liquid and boils at 685 °C to a dark yellow vapour. Selenium has a hexagonal polyatomic (CN 2) crystalline structure.

It is a semiconductor with a band gap of 1.7 eV, and a photoconductor meaning its electrical conductivity increases a million-fold when illuminated. Selenium has a moderate ionisation energy (941.0 kJ/mol), high electron affinity (195 kJ/mol), and high electronegativity (2.55). It is a poor oxidising agent (Se + 2 e − → H 2Se = −0.082 V at pH 0).

The chemistry of selenium is largely covalent in nature, noting it can form ionic selenides with highly electropositive metals. The common oxide of selenium is strongly acidic. Tellurium Tellurium is a silvery-white, moderately reactive, shiny solid, that has a density of 6.24 g/cm 3 and is soft (MH 2.25) and brittle. It is the softest of the commonly recognised metalloids. Tellurium reacts with boiling water, or when freshly precipitated even at 50 °C, to give the dioxide and hydrogen: Te + 2 H 2O → TeO 2 + 2 H 2.

It has a melting point of 450 °C and a boiling point of 988 °C. Tellurium has a polyatomic (CN 2) hexagonal crystalline structure. It is a semiconductor with a band gap of 0.32 to 0.38 eV. Tellurium has a moderate ionisation energy (869.3 kJ/mol), high electron affinity (190 kJ/mol), and moderate electronegativity (2.1). It is a poor oxidising agent (Te + 2 e − → H 2Te = −0.45 V at pH 0).

The chemistry of tellurium is largely covalent in nature, noting it has an extensive organometallic chemistry and that many tellurides can be regarded as metallic alloys. The common oxide of tellurium is amphoteric. Group 17. Liquid fluorine, in a cryogenic bath Fluorine is an extremely toxic and reactive pale yellow diatomic gas that, with a gaseous density of 1.696 × 10 −3 g/cm 3, is about 40% heavier than air. Its extreme reactivity is such that it was not isolated (via electrolysis) until 1886 and was not isolated chemically until 1986. Its occurrence in was first reported in 2012, but is contentious.

Fluorine condenses to a pale yellow liquid at −188.11 °C and freezes into a colourless solid at −219.67 °C. The solid form (density 1.7 g/cm −3) has a cubic crystalline structure and is soft and easily crushed. Fluorine is an insulator in all of its forms. It has a high ionisation energy (1681 kJ/mol), high electron affinity (328 kJ/mol), and high electronegativity (3.98). Fluorine is a powerful oxidising agent (F 2 + 2 e → 2HF = 2.87 V at pH 0); 'even water, in the form of steam, will catch fire in an atmosphere of fluorine'. Metal fluorides are generally ionic in nature. Chlorine gas Chlorine is an irritating green-yellow diatomic gas that is extremely reactive, and has a gaseous density of 3.2 × 10 −3 g/cm 3 (about 2.5 times heavier than air).

It condenses at −34.04 °C to an amber-coloured liquid and freezes at −101.5 °C into a yellow crystalline solid. The solid form (density 1.9 g/cm −3) has an orthorhombic crystalline structure and is soft and easily crushed. Chlorine is an insulator in all of its forms. It has a high ionisation energy (1251.2 kJ/mol), high electron affinity (349 kJ/mol; higher than fluorine), and high electronegativity (3.16). Chlorine is a strong oxidising agent (Cl 2 + 2 e → 2HCl = 1.36 V at pH 0). Metal chlorides are largely ionic in nature.

The common oxide of chlorine (Cl 2O 7) is strongly acidic. Liquid bromine Bromine is a deep brown diatomic liquid that is quite reactive, and has a liquid density of 3.1028 g/cm 3. It boils at 58.8 °C and solidifies at −7.3 °C to an orange crystalline solid (density 4.05 g/cm −3).

It is the only element, apart from mercury, known to be a liquid at room temperature. The solid form, like chlorine, has an orthorhombic crystalline structure and is soft and easily crushed. Bromine is an insulator in all of its forms. It has a high ionisation energy (1139.9 kJ/mol), high electron affinity (324 kJ/mol), and high electronegativity (2.96). Bromine is a strong oxidising agent (Br 2 + 2 e → 2HBr = 1.07 V at pH 0). Metal bromides are largely ionic in nature.

The unstable common oxide of bromine is strongly acidic. Iodine crystals Iodine, the rarest of the nonmetallic halogens, is a metallic looking solid that is moderately reactive, and has a density of 4.933 g/cm 3.

It melts at 113.7 °C to a brown liquid and boils at 184.3 °C to a violet-coloured vapour. It has an orthorhombic crystalline structure with a flaky habit.

Iodine is semiconductor in the direction of its planes, with a band gap of about 1.3 eV and a conductivity of 1.7 × 10 −8 S.cm −1 at room temperature. This is higher than selenium but lower than boron, the least electrically conducting of the recognised metalloids. Iodine is an insulator in the direction perpendicular to its planes. It has a high ionisation energy (1008.4 kJ/mol), high electron affinity (295 kJ/mol), and high electronegativity (2.66). Iodine is a moderately strong oxidising agent (I 2 + 2 e → 2I − = 0.53 V at pH 0).

Metal iodides are predominantly ionic in nature. The only stable oxide of iodine is strongly acidic. Astatine is expected to have properties intermediate between iodine, a nonmetal with incident metallic properties, and, which is predicted to be a metal. Astatine has not so far been synthesised in sufficient quantities to enable a determination of its bulk properties. A macro-sized sample of astatine would vaporise itself due to radioactive heating; it is not known if such a phenomenon could be prevented with sufficient cooling.

Many of the properties of astatine have nevertheless been predicted. It is expected to have a metallic appearance, a density of 6.35±0.15 g/cm 3, a melting point of 302 °C, a boiling point of 337 °C(?), and a face-centred cubic crystalline structure. It has a moderate ionisation energy (899.003 kJ/mol), and is expected to have a high electron affinity (222 kJ/mol), and moderate electronegativity (2.2). Astatine is a weak oxidizing agent (At + e → At − = 0.3 V at pH 0). Group 18. Liquified helium Helium has a density of 0.1785 × 10 −3 g/cm 3 (cf. Air 1.225 × 10 −3 g/cm 3), liquifies at −268.928 °C, and cannot be solidified at normal pressure.

It has the lowest boiling point of all of the elements. Liquid helium exhibits super-fluidity, superconductivity, and near-zero viscosity; its thermal conductivity is greater than that of any other known substance (more than 1,000 times that of copper). Helium can only be solidified at −272.20 °C under a pressure of 2.5 MPa. It has a very high ionisation energy (2372.3 kJ/mol), low electron affinity (estimated at −50 kJ/mol), and very high electronegativity (5.5 AR).

No normal have so far been synthesised. Neon in an electrical discharge tube Neon has a density of 0.9002 × 10 −3 g/cm 3, liquifies at −245.95 °C, and solidifies at −248.45 °C. It has the narrowest liquid range of any element and, in liquid form, has over 40 times the refrigerating capacity of liquid helium and three times that of liquid hydrogen.

Neon has a very high ionisation energy (2080.7 kJ/mol), low electron affinity (estimated at −120 kJ/mol), and very high electronegativity (4.84 AR). It is the least reactive of the noble gases; no normal have so far been synthesised. A small piece of rapidly melting solid argon Argon has a density of 1.784 × 10 −3 g/cm 3, liquifies at −185.848 °C, and solidifies at −189.34 °C. Although non-toxic, it is 38% denser than air and therefore considered a dangerous asphyxiant in closed areas.

It is difficult to detect because (like all the noble gases) it is colourless, odourless, and tasteless. Argon has a high ionisation energy (1520.6 kJ/mol), low electron affinity (estimated at −96 kJ/mol), and high electronegativity (3.2 AR). One interstitial, Ar 1C 60 is a stable solid at room temperature. Pressurized xenon gas encapsulated in an acrylic cube Xenon has a density of 5.894 × 10 −3 g/cm 3, liquifies at −161.4 °C, and solidifies at −165.051 °C.

It is non-, and belongs to a select group of substances that penetrate the, causing mild to full surgical when inhaled in high concentrations with oxygen. Xenon has a high ionisation energy (1170.4 kJ/mol), low electron affinity (estimated at −80 kJ/mol), and high electronegativity (2.4 AR). It forms a relatively, mostly containing fluorine or oxygen. An unusual ion containing xenon is the cation, AuXe 2+ 4, which contains Xe–Au bonds.

This ion occurs in the compound AuXe 4(Sb 2F 11) 2, and is remarkable in having direct chemical bonds between two notoriously unreactive atoms, xenon and, with xenon acting as a transition metal ligand. The compound Xe 2Sb 2F 11 contains a Xe–Xe bond, the longest element-element bond known (308.71 pm = 3.0871 ). The most common oxide of xenon is strongly acidic. Radon, which is radioactive, has a density of 9.73 × 10 −3 g/cm 3, liquifies at −61.7 °C, and solidifies at −71 °C.

It has a high ionisation energy (1037 kJ/mol), low electron affinity (estimated at −70 kJ/mol), and moderate electronegativity (2.06 AR). The only confirmed compounds of radon, which is the rarest of the naturally occurring noble gases, are the difluoride RnF 2, and trioxide, RnO 3. It has been reported that radon is capable of forming a simple Rn 2+ cation in halogen fluoride solution, which is highly unusual behaviour for a nonmetal, and a noble gas at that. Radon trioxide (RnO 3) is expected to be acidic.

Oganesson, the heaviest element on the periodic table, has only recently been synthesized. Owing to its short half-life, its chemical properties have not yet been investigated. Due to the significant relativistic destabilisation of the 7p 3/2 orbitals, it is expected to be significantly reactive and behave more similarly to the group 14 elements, as it effectively has four valence electrons outside a pseudo-noble gas core. Its boiling point is expected to be about 80±30 °C, so that it is probably neither noble nor a gas; as a liquid it is expected to have a density of about 5 g/cm 3. It is expected to have a barely positive electron affinity (estimated as 5 kJ/mol) and a moderate ionisation energy of about 860 kJ/mol, which is rather low for a nonmetal and close to those of the metalloids tellurium and astatine.

The oganesson fluorides OgF 2 and OgF 4 are expected to show significant ionic character, suggesting that oganesson may have at least incipient metallic properties. The oxides of oganesson, OgO and OgO 2, are predicted to be amphoteric. Cross-cutting relationships Some pairs of nonmetals show additional relationships, beyond those associated with group membership.

Hydrogen in group 1, and carbon in group 14, show some out-of-group similarities. These include proximity in ionization energies, electron affinities and electronegativity values; half-filled valence shells; and correlations between the chemistry of H–H and C–H bonds.

Just as the metalloids cluster along a diagonal path, similar diagonal relationships occur between carbon and phosphorus, and between nitrogen and sulfur. Carbon and phosphorus represent an example of a less-well known diagonal relationship, especially in organic chemistry. 'Spectacular' evidence of this relationship was provided in 1987 with the synthesis of a -like molecule in which six of the carbon atoms were replaced by phosphorus atoms.

Further illustrating the theme is the 'extraordinary' similarity between low coordinate phosphorus compounds and unsaturated carbon compounds, and related research into organophosphorus chemistry. Nitrogen and sufur have a less-well known diagonal relationship, manifested in like charge densities and electronegativities (the latter are identical if only the p electrons are counted; see Hinze and Jaffe 1962) especially when sulfur is bonded to an electron-withdrawing group. They are able to form an extensive series of seemingly interchangeable sulfur nitrides, the most famous of which, polymeric sulfur nitride, is metallic, and a superconductor below 0.26 K. The aromatic nature of the S 3N 2 2+ ion, in particular, serves as an 'exemplar' of the similarity of electronic energies between the two nonmetals. Fluorine and oxygen share the ability to often bring out the highest oxidation states among the elements. 'Chlorination reactions have many similarities to oxidation reactions. They tend not to be limited to thermodynamic equilibrium and often go to complete chlorination.

The reactions are often highly exothermic. Chlorine, like oxygen, forms flammable mixtures with organic compounds.' The chemistry of iodine in its oxidation states of +1, +3, +5, and +7 is analogous to that of xenon in an immediately higher oxidation state. Allotropes. Some allotropes of carbon Many nonmetals have less stable, with either nonmetallic or metallic properties.

Graphite, the standard state of carbon, has a lustrous appearance and is a fairly good electrical conductor. The diamond allotrope of carbon is clearly nonmetallic, however, being translucent and having a relatively poor electrical conductivity. Carbon is also known in several other allotropic forms, including semiconducting (C 60). Nitrogen can form gaseous (N 4), an unstable polyatomic molecule with a lifetime of about one microsecond. Oxygen is a diatomic molecule in its standard state; it also exists as (O 3), an unstable nonmetallic allotrope with a half-life of around half an hour. Phosphorus, uniquely, exists in several allotropic forms that are more stable than that of its standard state as white phosphorus (P 4). The and allotropes are probably the best known; both are semiconductors.

Phosphorus is also known as (P 2), an unstable diatomic allotrope. Sulfur has more allotropes than any other element; all of these, except plastic sulfur (a metastable mixture of allotropes) have nonmetallic properties. Selenium has several nonmetallic allotropes, all of which are much less electrically conducting than its standard state of grey 'metallic' selenium. Iodine is also known in a semiconducting amorphous form. Under sufficiently high pressures, just over half of the nonmetals, starting with phosphorus at 1.7 GPa, have been observed to form metallic allotropes. Most metalloids, like the less electronegative nonmetals, form allotropes. Boron is known in.

The discovery of a quasispherical allotropic molecule (B 40) was announced in July 2014. Silicon was most recently known only in its crystalline and amorphous forms., a two-dimensional allotrope of silicon, with a hexagonal honeycomb structure similar to that of, was observed in 2010. The synthesis of an orthorhombic allotrope Si 24, was subsequently reported in 2014. At pressure of 10–11 GPa, germanium transforms to a metallic phase with the same tetragonal structure as tin; when decompressed—and depending on the speed of pressure release—metallic germanium forms a series of allotropes that are metastable at ambient condition. Germanium also forms a graphene analogue,.

Arsenic and antimony form several well known allotropes (yellow, grey, and black). Tellurium is known only in its crystalline and amorphous forms; astatine is not known to have any allotropes. Abundance and extraction.

A source of fluorine Hydrogen and helium are estimated to make up approximately 99 per cent of all ordinary matter in the universe. Less than five per cent of the Universe is believed to be made of ordinary matter, represented by stars, planets and living beings. The balance is made of and, both of which are poorly understood at present. Hydrogen, carbon, nitrogen, and oxygen constitute the great bulk of the Earth's atmosphere, oceans, crust, and biosphere; the remaining nonmetals have abundances of 0.5 per cent or less. In comparison, 35 per cent of the crust is made up of the metals, and; together with a metalloid,. All other metals and metalloids have abundances within the crust, oceans or biosphere of 0.2 per cent or less. Nonmetals, and metalloids, in their elemental forms are extracted from:: Cl, Br, I; liquid air: N, O, Ne, Ar, Kr, Xe; minerals: B ; C (coal; diamond; graphite); F ; Si P (phosphates); Sb (, ); I (in sodium iodate NaIO 3 and sodium iodide NaI); natural gas: H, He, S; and from ores, as processing byproducts: Ge (zinc ores); As (copper and lead ores); Se, Te (copper ores); and Rn (uranium bearing ores).

Astatine is produced in minute quantities by irradiating bismuth. A high-voltage employing SF 6 as its inert (air replacement) interrupting medium Nonmetals do not have any universal or near-universal applications. This is not the case with metals, most of which have structural uses; nor the metalloids, the typical uses of which extend to (for example) oxide glasses, alloying components, and semiconductors. An ionisation energy of less than 750 kJ/mol is taken to be low, 750–1000 is moderate, and  1000 is high ( 2000 is very high); an electron affinity of less than 70 kJ/mol is taken to be low, 70–140 is moderate, and  140 is high; an electronegativity of less than 1.8 is taken to be low; 1.8–2.2 is moderate; and than 2.2 is high ( 4.0 is very high).

. The can be broadly divided into, and according to their shared and.

All metals have a shiny appearance (at least when freshly polished); are good conductors of heat and electricity; form with other metals; and have at least one. Metalloids are metallic-looking brittle solids that are either or exist in semiconducting forms, and have or weakly. Typical nonmetals have a dull, coloured or colourless appearance; are when solid; are poor conductors of heat and electricity; and have acidic oxides. Most or some elements in each category share a range of other properties; a few elements have properties that are either anomalous given their category, or otherwise extraordinary. Main article: Metals appear lustrous (beneath any ); form mixtures when combined with other metals; tend to lose or share electrons when they react with other substances; and each forms at least one predominantly basic oxide.

Most metals are silvery looking, high density, relatively soft and easily deformed solids with good and, low and, and are found naturally in combined states. Some metals appear coloured (, ), have low (e.g., ) or very, are liquids at or near room temperature, are brittle (e.g., ), not easily machined (e.g., ), or are noble (hard to ) or have nonmetallic structures ( and are structurally analogous to, respectively, and ). Metals comprise the large majority of the elements, and can be subdivided into several different categories.

From left to right in the periodic table, these categories include the highly reactive; the less reactive, and radioactive; the archetypal, and the physically and chemically weak. Specialized subcategories such as the and the also exist. Metalloids.

Main article: Nonmetals have open structures (unless solidified from gaseous or liquid forms); tend to gain or share electrons when they react with other substances; and do not form distinctly basic oxides. Most are gases at room temperature; have relatively low densities; are poor electrical and thermal conductors; have relatively high ionisation energies and electronegativities; form acidic oxides; and are found naturally in uncombined states in large amounts. Some nonmetals (, and ) are brittle solids at room temperature (although each of these also have malleable, pliable or ductile allotropes). From left to right in the periodic table, the nonmetals can be subdivided into the which, being nearest to the metalloids, show some incipient metallic character, and the monatomic, which are almost completely inert. (or that are relatively distinct) Resemble metals Relatively distinct Resemble nonmetals Properties compared: (36) 7 (19%) 25 (68%) 5 (13%) Physical (21) 5 (24%) 14 (67%) 2 (10%).

(10) 2 6 2 (20%). (6) 1 5. (5) 2 3 Chemical (16) 2 (13%) 11 (69%) 3 (19%).

(6) 3 3 (50%). (6) 2 4. (4) 4 The characteristic properties of metals and nonmetals are quite distinct, as shown in the table below. Metalloids, straddling the, are mostly distinct from either, but in a few properties resemble one or the other, as shown in the shading of the metalloid column below and summarized in the small table at the top of this section. Authors differ in where they divide metals from nonmetals and in whether they recognize an intermediate category.

Some authors count metalloids as nonmetals with weakly nonmetallic properties. Others count some of the metalloids as. ” Oliver Sacks (2001, p. 204) Within each category, elements can be found with one or two properties very different from the expected norm, or that are otherwise notable. Metals ,. The common notions that 'alkali metal ions (group 1A) always have a +1 charge' and that 'transition elements do not form anions' are errors.

The synthesis of a crystalline salt of the sodium anion Na − was reported in 1974. Since then further compounds (') containing anions of all other except and, as well as that of, have been prepared. In 1943, Sommer reported the preparation of the yellow transparent compound. This was subsequently shown to consist of caesium cations (Cs +) and auride anions (Au −) although it was some years before this conclusion was accepted. Several other aurides (KAu, RbAu) have since been synthesized, as well as the red transparent compound Cs 2Pt which was found to contain Cs + and Pt 2− ions.

Well-behaved metals have crystal structures featuring with up to four atoms. Manganese has a complex crystal structure with a 58-atom unit cell, effectively four different atomic radii, and four different (10, 11, 12 and 16). It has been described as resembling 'a quaternary with four Mn atom types bonding as if they were different elements.' The half-filled 3d shell of manganese appears to be the cause of the complexity. This confers a large on each atom. Below 727 °C, a unit cell of 58 spatially diverse atoms represents the energetically lowest way of achieving a zero net magnetic moment.

The crystal structure of manganese makes it a hard and brittle metal, with low electrical and thermal conductivity. At higher temperatures 'greater lattice vibrations nullify magnetic effects' and manganese adopts less complex structures.,. The only elements strongly attracted to magnets are iron, cobalt, and nickel at room temperature, gadolinium just below, and terbium, dysprosium, holmium, erbium, and thulium at ultra cold temperatures (below −54 °C, −185 °C, −254 °C, −254 °C, and −241 °C respectively).

The only element encountered with an oxidation state of +9 is iridium, in the IrO 4 + cation. Other than this, the highest known oxidation state is +8, in, and.

The of gold is extraordinary: a fist sized lump can be hammered and separated into one million paper back sized sheets, each 10 thick1600 times thinner than regular kitchen aluminium foil (0.016 mm thick). Bricks and bowling balls will float on the surface of mercury thanks to it having a density 13.5 times that of water. Equally, a solid mercury bowling ball would weigh around 50 pounds and, if it could be kept cold enough, would float on the surface of liquid. The only metal having an ionisation energy higher than some nonmetals ( and ) is mercury. Mercury and its compounds have a reputation for toxicity but on a scale of 1 to 10, ((CH 3) 2Hg) (abbr.

DMM), a volatile colourless liquid, has been described as a 15. It is so dangerous that scientists have been encouraged to use less toxic mercury compounds wherever possible. In 1997, a professor of chemistry specialising in toxic metal exposure, died of mercury poisoning ten months after a few drops of DMM landed on her 'protective' latex gloves.

Although Wetterhahn had been following the then published procedures for handling this compound, it passed through her gloves and skin within seconds. It is now known that DMM is exceptionally permeable to (ordinary) gloves, skin and tissues. And its toxicity is such that less than one-tenth of a ml applied to the skin will be seriously toxic. The expression, to ' is anchored in the common view of lead as a dense, heavy metal—being nearly as dense as mercury.

However, it is possible to construct a balloon made of lead foil, filled with a and air mixture, which will float and be buoyant enough to carry a small load. Bismuth has the longest of any naturally occurring element; its only, was found in 2003 to be slightly, decaying via with a more than a billion times the estimated. Prior to this discovery, bismuth-209 was thought to be the heaviest naturally occurring stable isotope; this distinction now belongs to lead-208. The only element with a naturally occurring isotope capable of undergoing nuclear fission is uranium. The capacity of to undergo fission was first suggested (and ignored) in 1934, and subsequently discovered in 1938. It is a commonly held belief that metals reduce their electrical conductivity when heated. Plutonium increases its electrical conductivity when heated in the temperature range of around –175 to +125 °C.

Metalloids. Boron is the only element with a partially disordered structure in its most thermodynamically stable crystalline form.

These elements are record holders within the field of chemistry. For seven decades, HSO 3F and CF 3SO 3H were the strongest known acids that could be isolated as single compounds. Both are about a thousand times more acidic than pure. In 2004, a boron compound broke this record by a thousand fold with the synthesis of H(CHB 11Cl 11). Another metalloid, antimony, features in the strongest known acid, a mixture 10 billion times stronger than carborane acid.

This is H 2FSbF 6, a mixture of SbF 5 and HF. The thermal conductivity of silicon is better than that of most metals. A sponge-like form of silicon (p-Si) is typically prepared by the electrochemical etching of silicon wafers in a solution. Flakes of p-Si sometimes appear red; it has a band gap of 1.97–2.1 eV.

The many tiny pores in porous silicon give it an enormous internal surface area, up to 1,000 m 2/cm 3. When exposed to an, especially a liquid oxidant, the high surface-area to volume ratio of p-Si creates a very efficient burn, accompanied by nano-explosions, and sometimes by -like plasmoids with, for example, a diameter of 0.1–0.8 m, a velocity of up to 0.5 m/s and a lifetime of up to 1s.

The first ever spectrographic analysis of a ball lightning event (in 2012) revealed the presence of silicon, iron and calcium, these elements also being present in the soil. Metals are said to be, resulting in some confusion in old chemistry as to whether arsenic was a true metal, or a nonmetal, or something in between.

It rather than melts at standard, like the nonmetals and. A high-energy explosive form of antimony was first obtained in 1858. It is prepared by the electrolysis of any of the heavier antimony trihalides (SbCl 3, SbBr 3, SbI 3) in a hydrochloric acid solution at low temperature.

It comprises amorphous antimony with some occluded antimony trihalide (7–20% in the case of the ). When scratched, struck, powdered or heated quickly to 200 °C, it 'flares up, emits sparks and is converted explosively into the lower-energy, crystalline grey antimony.' Nonmetals. (H 2O), a well known of hydrogen, is a spectacular anomaly. Extrapolating from the heavier, namely H 2S, H 2Se, and H 2Te, water should be 'a foul-smelling, poisonous, inflammable gascondensing to a nasty liquid at around –100° C'. Instead, due to, water is 'stable, potable, odorless, benign, andindispensable to life'. Less well known of the oxides of hydrogen is the, H 2O 3.

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Proposed the existence of this oxide in 1880 but his suggestion was soon forgotten as there was no way of testing it using the technology of the time. Hydrogen trioxide was prepared in 1994 by replacing the oxygen used in the industrial process for making hydrogen peroxide, with. The yield is about 40 per cent, at –78 °C; above around –40 °C it decomposes into water and oxygen. Derivatives of hydrogen trioxide, such as F 3C–O–O–O–CF 3 ('bis(trifluoromethyl) trioxide') are known; these are at room temperature. Went a step further, in 1895, and proposed the existence of HO–O–O–OH as a transient intermediate in the decomposition of hydrogen peroxide; this was prepared and characterised in 1974, using a matrix isolation technique.

salts of the unknown (HO 3) are also known; these have the formula MO 3. At temperatures below 0.3 and 0.8 K respectively, and each have a negative. This means that, at the appropriate constant pressures, these substances freeze with the addition of heat.

Bmw r1200rt 2017 manual. With a generous wheelbase and rake, the R 1200 RT is a smooth highwayman. The big change for the coast-to-coast sport-touring runner is ABS Pro. 2018 BMW R 1200 RT An iconic long-distance tourer, the 2018 BMW R 1200 RT has a classic boxer twin as its centerpiece, albeit updated to feature both liquid- and air-cooling.

Until 1999 helium was thought to be too small to form a cage —a compound in which a guest atom or molecule is encapsulated in a cage formed by a host molecule—at atmospheric pressure. In that year the synthesis of microgram quantities of represented the first such helium clathrate and (what was described as) the world's smallest helium balloon. Graphite is the most electrically conductive nonmetal, better than some metals. is the best natural conductor of heat; it even feels cold to the touch. Its thermal conductivity (2,200 W/m.K) is five times greater than the most conductive metal ( at 429); 300 times higher than the least conductive metal ( at 6.74); and nearly 4,000 times that of water (0.58) and 100,000 times that of air (0.0224). This high thermal conductivity is used by jewelers and gemologists to separate diamonds from imitations.

Graphene, produced in 2012 by freeze-drying a solution of and sheets and chemically removing oxygen, is seven times lighter than air, and ten per cent lighter than helium. It is the lightest solid known (0.16 mg/cm 3), conductive and elastic. The least stable and most reactive form of phosphorus is the.

It is a hazardous, highly flammable and toxic substance, spontaneously igniting in air and producing residue. It is therefore normally stored under water. White phosphorus is also the most common, industrially important, and easily reproducible allotrope, and for these reasons is regarded as the of phosphorus. The most stable form is the, which is a metallic looking, brittle and relatively non-reactive semiconductor (unlike the white allotrope, which has a white or yellowish appearance, is pliable, highly reactive and a semiconductor). When assessing periodicity in the physical properties of the elements it needs to be borne in mind that the quoted properties of phosphorus tend to be those of its least stable form rather than, as is the case with all other elements, the most stable form. The mildest of the, iodine is the active ingredient in, a disinfectant.

This can be found in household medicine cabinets or emergency survival kits. Tincture of iodine will rapidly dissolve gold, a task ordinarily requiring the use of (a highly corrosive mixture of and ). Notes. ^.

^. Columns 2 (metals) and 4 (nonmetals) are sourced from this reference unless otherwise indicated. ^.

Chang speculates that the melting point of francium would be about 23 °C.;;;. ^.;.;.;.;;.;.;.;. ^.;. ^.;.;.;.: ', and are considered to be semimetals. In bulk semimetals. The resistivity will increase with temperature.

To give a positive temperature coefficient of resistivity.' .: 'Nonmetals mostly have negative temperature coefficients.

For instance, carbon. has a resistance that decreases with a rise in temperature.

However, recent experiments on very pure graphite, which is a form of carbon, have shown that pure carbon in this form behaves similarly to metals in regard to its resistance.' .

^. ^.;.;.;.;.;.;. ^;;. ^.;.;.: 'This story was told by Glenn Seaborg when he was presenting his recollections at a conference in November 1997.' .;. ^. ^.; see also.; see also.

^. ^.;.;. References.