Nature of Solids

Objectives:• 1.Compare the properties of crystalline solids

with those of amorphous solids.• 2.Foreach type of solid, relate its structure and

bonding to its properties.KeyTerms:• crystalline solid, anhydrous, amorphous solid,

covalent-network solid

Nature of Solids

Basic Properties:• Solids, unlike liquids, have atoms and molecules in fixed

positions– solids have strong intermolecular forces– Solids have a definite shape and volume

• The density of most solids is only slightly greater than the liquid phase of the same material – Exception is with water

• KE of Molecules (atoms) is less than the energy it takes to separate them– A solid become liquid at its melting point

• KE = intermolecular forces

Basic Physical Properties

The physical properties solids of substances are dependent mostly on the intermolecular bonds.• hardness • melting point • electrical conductivity • luster • fracture • tensile strength • malleability • ductile

Crystalline SolidsA crystalline solid is one in which the molecules or atoms are arranged in highly ordered repeating patterns.• Most solids are crystalline • The smallest repeating unit is called a unit cell (think of a honeycomb) • Some crystals exist as hydrates (having water molecules) - CuSO4 * 5H2O

(copper sulfate pentahydrate) has 5 water molecules included in each of its cells

• Anhydrous crystalline solids are completely free of water

Amorphous Solids

Solids that do not form crystals and do not behave as solids are called amorphous (without form).• plastic, rubber, glass • Covalently bonded

Allotropes

• solid substances that are different molecular form but have the same composition

Type of Solid - Metallic

• Bond Type - Metallic bond • Hardness - Soft to hard– low to high melting point

• Conductivity - electrical and thermal conductivity

• Malleable & ductile

Type of Solid - Molecular

• Particles - atoms or molecules • Bond Type - Hydrogen bond, dipole-dipole,

dispersion (temporary) • Hardness – soft– low to moderately high melting point

• Conductivity - poor electrical and thermal conductivity

• Other - most organic & inorganic compounds (methane, sugar, water)

Type of Solid - Ionic

• Particles - Positive & negative ions• Bonds - electrostatic attractions • Hardness - Hard, brittle – high melting point

• Conductivity - poor electrical and thermal conductivity

• Other - ionic salts (NaCl, KBr, MgSO4)

Type of Solid - Covalent-Network

• Particles – non-metals• Bonds - Covalent bonds • Hardness - very hard, brittle– very high melting point

• Conductivity - often poor electrical and thermal conductivity

• Other - diamond, Silicon, quartz, graphite