Nonmetals

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Sections 22.1-22.4Chemistry of the

Nonmetals

Chemistry, The Central Science, 11th editionBrown & LeMay

Nonmetals

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Nonmetals

Except for hydrogen, the nonmetals are found in the upper right-hand corner of the periodic chart.

Nonmetals

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Periodic Trends

Within a group, smaller atoms are more likely to form -bonds because they can get closer to other atoms.

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Periodic Trends

As a result, CO2 contains two -bonds, and SiO2 is a network solid with only -bonds.

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Hydrogen:

• It was discovered by Henry Cavendish (1731–1810).

• There are three isotopes:– Protium (1H): 99.98% of

all hydrogen.– Deuterium (2H): 0.016% of

all hydrogen– Tritium (3H): Radioactive

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Properties of Hydrogen

• Hydrogen is unique.– It does not belong to any group.

• It has very low melting (−259 °C) and boiling (−253 °C) points.

• It has very large bond enthalpies.– Therefore, it reacts slowly,– And its reactions are generally quite

exothermic.

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Hydrogen Production

• Hydrogen is commercially produced from reaction of methane (CH4) with steam at 1100°C or carbon

and steam above 1000°C.

CH4(g) + H2O(g) CO(g) + 3 H2(g)

CO(g) + H2O(g) CO2(g) + H2(g)

C(s) + H2O(g) H2(g) + CO(g)

• Its production from the electrolysis of water is not energy efficient.

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Uses of Hydrogen

• Most hydrogen is used to produce ammonia (NH3) in the Haber process.

• It is also used to produce methanol (CH3OH).

CO(g) + 2 H2(g) CH3OH(g)

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Uses of Hydrogen

• Using hydrogen as a fuel would have many advantages:– It's reaction with water is highly exothermic.– Water is the only product

• Problem: How will we make the H2?

2 H2(g) + O2(g) 2 H2O(g) H = −483.6 kJ

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Hydrides

• There are three types of hydrides:– Ionic– Metallic– Molecular

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Ionic Hydrides• Ionic hydrides are

formed between hydrogen and alkali metals or heavy alkaline earth metals (Ca, Sr, Ba).

• They are very strong bases and reducing agents.

• They react readily with water, so they must be stored free from moisture.

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Metallic Hydrides

• These are formed between hydrogen and transition metals, often in unusual ratios.– TiH1.8, for example.

• They retain electrical conductivity and other metallic properties.

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Molecular Hydrides

• These are formed between hydrogen and nonmetals or metalloids.

• They are usually gases or liquids at room temperature and normal atmospheric pressure.

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Xenon Compounds

• Of all noble gases, Xe can be forced to form compounds most easily.

• KrF2 is also known, but decomposes at −10°C.

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Halogens• The halogens have

outer electron configurations of ns2np5.

• They have large electron affinities and ionization energies.

• They tend to accept one electron to form anions.

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Halogens

• All have a −1 oxidation state.

• All but fluorine also have positive oxidation states up to +7 when bonded to more electronegative atoms.

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Properties of Halogens

• They tend to be good oxidizers, due to their electronegativity.

• They can oxidize anions of halides below them on periodic chart.

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Properties of Halogens

• Fluorine has an unusually high reduction potential.• It can easily oxidize water.

F2(aq) + H2O(l) 2 HF(aq) + 1/2 O2(g) E° = 1.80 V

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Uses of Halogens

• Fluorine reacts to form fluorocarbon compounds used as lubricants, refrigerants and plastics.

• Teflon is a polymer of fluorocarbons.

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Uses of Halogens

• Chlorine is the most-used halogen.– HCl– Plastics– Bleaches– Water purification

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Uses of Halogens

• Bromine is the anion for silver in photographic film.

• KI is added to table salt as a dietary supplement.

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Hydrogen Halides

• Aqueous solutions of HCl, HBr, and HI are, of course, strong acids.

• HF and HCl can be produced by reacting salts with H2SO4.

• Br− and I− oxidize too easily, so one must use a weaker oxidizing acid, like H3PO4.

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HF

• Hydrofluoric acid reacts with silicates, components of most types of glass.

• This reaction causes glass to etch.

• Therefore, HF is usually stored in plastic containers.