Properties of Solids

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steel = iron + carbon

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Network Atomic Solids

Some covalently bonded substances DO NOT form discrete molecules.

Diamond, a network of covalently bonded carbon atoms

Graphite, a network of covalently bonded carbon atoms

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Graphene

Graphene can be described as a one-atom thick layer of graphite.

Source: Wikipedia

High-quality graphene is strong, light, nearly transparent and an excellent conductor of heat and electricity.

Andre Geim and Konstantin Novoselov at the University of Manchester won the Nobel Prize in Physics in 2010 "for groundbreaking experiments regarding the two-dimensional material graphene"

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Semiconductors

Pure silicon is structurally the same as diamond, but is a semiconductor rather than an insulator.

The conductivity increases at higher temperature.

Conductivity of silicon can be improved by doping with other elements.

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n-type Semiconductors

Substances whose conductivity is increased by doping with atoms having more valence electrons than the host crystal. Here, silicon (4 valence e-’s) is doped with phosphorus (5 valence e-’s).

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p-type Semiconductors

Substances whose conductivity is increased by doping with atoms having fewer valence electrons than the host crystal. Here, silicon (4 valence e-’s) is doped with aluminum (3 valence e-’s).

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Molecular Solids

Strong covalent forces within molecules

Weak covalent forces between molecules

Sulfur, S8

Phosphorus, P4

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Ionic Solids

Sodium Fluoride

Ionic compounds at room conditions are generally crystal lattices of alternating cations and anions.

Sodium chloride and sodium fluoride form simple cubic crystals.

NaCl Unit Cell

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Ionic Solids

Lithium niobate, LiNbO3

Ionic compounds are represented by empirical formulas, because they do not form discrete molecular structures.