The Structure and Properties of Solids

Ionic Crystals This ionic bond forms from the interaction of metal (sodium) and non-metal (chloride) ions. The ions arrange in a crystal lattice structure with alternating packing of the positive and negative ions. Physical Properties Hard, brittle solid When dissolves in water, the solution conducts electricity High melting points as a result of the strong electrostatic forces Ex. NaCl, MgO

Metallic Crystals In the solid state metals form a metallic crystal, which is a structure composed of closely packed atoms held together by electrostatic interactions and free- moving electrons. Electron sea theory  a theory that states that the electrons in a metallic crystal move freely around the positively charged nuclei

Metallic Crystals Unlike ionic crystals, all metallic crystals do not have similar properties. Ex. Gold is soft and easily moulded while aluminum is harder. Physical Properties Shiny or silvery Melting points can vary, but most have fairly high Most are fairly strong Malleable

Molecular Crystals Some substances form crystal lattice structures when in the solid state. Molecular crystals are similar to ionic crystal lattices except that they are often more complex. Ex. Water can form several different types of structures in the frozen form. Example No two snowflakes will every look alike.

Molecular Crystals The intermolecular forces within a molecular crystal determine its structure and properties. Polar molecules -> have dipole-dipole forces <-very strong force Non-Polar  have London dispersion forces <-very weak force Physical Properties Do not conduct electricity Have lower melting points Less hard than ionic crystals

Covalent Network Crystals Is a solid in which the covalent bonds between atoms from an interwoven network. Diamond The hardest naturally occurring substance on earth The carbon atoms in a diamond molecule form a tetrahedral shape Physical Properties Very high melting points Extreme hardness The covalent network is very strong. The strength comes from the interlocking network structure. Poor conductors of electricity.

Covalent Network Crystals Carbon atoms can form other structures in addition to the structure found in diamond. Carbon atoms can form layers or sheets when in the solid phase or large spherical molecules.

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