Chemistry Video 8 Flashcards
Intermolecular forces
Electrostatic interactions between molecules. Not actual chemical bonds.
Ion-ion interactions
An intermolecular force.
Interactions between formally charged ions. For large ionic solids. The strongest intermolecular force because it involves formal charges.
Between formal charges
Ion-dipole interactions
An intermolecular force.
Dipole and ion interact. Dipole’s partially positive side attracts partially negative side.
Between a formal charge and a partial charge
Dipole-dipole interactions
An intermolecular force.
Dipoles interact with each other.
Between partial charges
Hydrogen bonds
An intermolecular force.
Dipoles generated by NH, OH or FH bonds. Especially strong dipole-dipole interactions because the elements are the most electronegative
Between partial charges
London dispersion
An intermolecular force.
Any substance can make this. Momentary dipole. Weaker than formal dipole. Becomes significant for larger molecules
Between momentary dipoles
Order of intermolecular force strength
Ion-Ion > Ion-dipole > H bond > Dipole-dipole > Dispersion
Electrostatic interactions
Every substance has this between its molecules. The stronger the electrostatic interactions, the more the molecules stick together.
Particles in solid or liquid are closer together than those in gases. Intermolecular force is between solids and liquids, but not between gases.
The stronger the attraction between particles, the more heat energy that needs to be provided in order to overcome the attractions and put the substance into the gas phase. More heat energy means higher boiling point
Condensation
When water vapour in the atmosphere cools, it will condense. Going from gas to liquid. As they cool, the molecules travel slower and begin to stick together
Change in temperature
Results in change in kinetic energy, which makes the molecules stick together more or less efficiently
Comparing interactions
- Which is the strongest type of interaction each substance can do? (i.e. H-bonds vs dispersion)
- If it is the same type of interaction, which does it better? (i.e. The larger the atom, the larger the surrounding electron cloud and the more significant the momentary dipole that can be produced.) The larger the atom, the stronger the dispersion interaction and the larger the boiling point.
Melting point determination
More branching in a molecule = more compact = ‘higher’ melting point
More linear = less compact = weaker interactions = ‘lower’ melting point
Crystalline solids
Have a repeating lattice structure.
Can be categorized as molecular solids, network solids, ionic solids or metallic solids
Molecular solids
A type of crystalline solid
The solid phase for small molecules. (i.e. water freezes to ice). Lowest melting and boiling points
Network solids
A type of crystalline solid
Covalently bonding throughout the solid.
Ex. diamond, quartz
Ionic solids
A type of crystalline solid
Ions that form a particular lattice structure to maximize electrostatic interactions between formally charged particles
May have unit cells, which have particular geometries depending on the identity of the cation/anion and the ratio of cation/anion. (i.e. one ion is larger than the other so there is a certain ratio). Can be cubic, face-centred, body-centred, tetragonal, orthorhombic, monoclinic, hexagonal, rhombohedral, or triclinic. The configuration adopted is the one that will maximize the electrostatic interaction between the ions
Metallic solids
A type of crystalline solid
Any metal, whose atoms form a network just like network solids. The metallic bonds that connect them are a bit different than regular covalent bonds, because electrons can delocalize and move freely in the system, allowing for electricity to be conducted
gold
Amorphous solids
no repeating lattice structure, because the molecular is large and do not have organization
glass, polymers, gels
Simple cubic cell
A type of unit cell. Part of ionic solids.
1 atom/unit cell. 1/8th of an atom at each corner
Face-centered cubic cell
A type of unit cell. Part of ionic solids.
4 atoms/unit cell. 1/8th atom at each corner and 1/2 atom on each face
Body-centered cubic cell
A type of unit cell. Part of ionic solids.
2 atoms/unit cell. 1/8th of an atom at each corner and 1 atom at the centre
Phase changes
They are physical changes.
Melting and freezing occurs between solid and liquids.
Boiling (vaporizing) and condensing is between liquid and gas
Sublimation is solid to gas. Deposition is gas to solid.
Phase diagrams
Phase of substance depends on the surrounding temperature and pressure, shown on diagram. Shows the solid-gas, solid-liquid and liquid-gas phase transitions for a particular substance
Temperature on x axis and pressure on y axis
Lines on phase diagram
Indicate equilibria between 2 phases
Triple point
On phase diagram. Is when there is an equilibrium between all 3 phases
Supercritical fluid; critical point
When the boundary between liquid and gas phase disappears. The substance would have properties in between a liquid and gas
Found on phase diagram, represented by critical point
Fills its container just like a gas. Its density is similar to liquid
Vapour pressure
Vapour pressure is a measure of the tendency of a material to change into the gaseous or vapour state, and it increases with temperature
