Types of Solids 10.5-10.7 Presentation

10.5 Carbon and Silicon: Network Atomic Solids A. Network Solids – Atomic solids with strong directional covalent bonds We can view them as giant molecules Brittle and do not conduct heat or electricity well

Diamond Network solid composed entirely of carbon atoms (Carbon-60) Each carbon in the structure is surrounded by a tetrahedral arrangement of other carbon atoms Structure is held together and stabilized with covalent bonds that are formed by the overlap of sp3 hybridized orbitals Because of a large gap between the occupied and unoccupied orbitals, diamond is a poor conductor of heat and electricity but it’s a great insulator

Graphite Slippery, soft, brittle, carbon based substance (Carbon-10) Graphite is a great conductor of electricity Structure is based on layers of carbon atoms formed in 6 member rings Each carbon in one layer is surrounded by 3 other carbon atoms in a trigonal planar arrangement with sp2 hybridization Pie bonds between layers make the structure stable and also contribute to the conductivity because of the delocalized electrons associated with them Strong bonding within the layers but weak between

silica SiO2 Silicon is different from carbon because it cannot use its 3p orbitials to form pie bonds with oxygen because its larger than carbon Because of this, silicon cannot form a double bond with oxygen and so the silica structure is all single bonded Quartz is based on a SiO4 tetrahedron Main component of glass, which is an amorphous solid

10.6 Molecular Solids Lattice positions are occupied by discrete molecular units so we can think of these types of solids as one giant molecule Strong covalent bonding takes place within the molecules that occupy the lattice positions, but weak attractive forces exist between the molecules in the structure Examples: Ice, Dry Ice, S8, Generally the attractive forces between the molecules is London Dispersion And as the size of the molecules increases, so does the strength of the London Dispersion forces Hydrogen bonding can enhance the strength of the LDF’s

10.8 Vapor Pressure

Variations in Vapor PRessures Liquids with greater intermolecular forces will have relatively lower vapor pressures This is because the attractions between the molecules are significant, and need to be overcome before the liquid particles can move into the gas phase Liquids with low intermolecular forces (weak attractions) will have higher vapor pressures Less energy is required to break up the attractive forces between the molecules

Terms 2. Heat of Fusion – energy required to convert 1 mole of a solid substance to a mole of liquid substance 3. Normal Melting Point – Temperature at which the solid and liquid phases have the same vapor pressure under conditions where the total pressure is 1 atm 4. Normal Boiling Point – temperature at which the vp of the liquid is exactly 1 atm

Supercooling Process where a liquid is cooled quickly and so it remains a liquid at a temperature where it should be a solid (frozen) 1. The quick temperature change does not allow time for the organization of the molecules into an orderly solid structure Once the particles find each other, the structure takes shape quickly, and it appears that is freezes “instantly”

Superheating Process of rapid heating of a liquid to a temperature above its normal boiling point (should be a gas but its not) In this process, not enough high energy molecules accumulate in one place to form bubbles and escape When they do the bubbles are large and it appears that the liquid explodes This situation is avoided in lab with boiling chips that provide spots for small normal sized bubbles to accumulate Works best with distilled water (no ions, no sites for accumulation of bubbles)