CHEM1312H - Metallic, Molecular, and Covalent Network Solids

molecular solds

-lattice sites in a crystalline molecular solid are occupied by atoms or molecules

-have strong covalent bonds within each molecule but weaker IMFs between molecules occupying the lattice points

-due to the weak IMFs some molecular solids are gases at room temperature

-low melting points because of weaker IMFs

-as the size of the molecules increase, LDFs increase, and they become solids

non-bending atomic solids

-consists of atoms held together by LDFs

-because these IMFs are weak, atomic solids are soft and have relatively low melting points

the electron sea model

-metallic solids have metal atoms (or ions) at the lattice points in a unit cell

-bonds occur in this model because the valence electrons are delocalized throughout the entire solid (not associated with a specific atom or bond but spread throughout the solid) due to low ionization energies

-as a result, metals have properties such as malleability, ductility, relatively high melting points, and conduction of heat and electricity

covalent network solids

-composed entirely of a 3D network of covalently bonded atoms at the lattice points

-the carbon atoms are sp³ hybridized and held together by strong carbon-carbon single covalent bonds

-the strength of these bonds impart network covalent a very high melting point

-very hard, brittle, and do not conduct electricity efficiently

covalent network solids (graphite)

-in contrast to diamond, graphite consists of sheets of carbon atoms that are covalently bonded to each other (each atom is sp² hybridized)

-the sheets are held together by dispersion forces creating slipperiness between layers