Chemistry Video 8

Question 1

Intermolecular forces

Answer 1

Electrostatic interactions between molecules. Not actual chemical bonds.

Question 2

Ion-ion interactions

Answer 2

An intermolecular force.

Interactions between formally charged ions. For large ionic solids. The strongest intermolecular force because it involves formal charges.

Between formal charges

Question 3

Ion-dipole interactions

Answer 3

An intermolecular force.

Dipole and ion interact. Dipole’s partially positive side attracts partially negative side.

Between a formal charge and a partial charge

Question 4

Dipole-dipole interactions

Answer 4

An intermolecular force.

Dipoles interact with each other.

Between partial charges

Question 5

Hydrogen bonds

Answer 5

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

Question 6

London dispersion

Answer 6

An intermolecular force.

Any substance can make this. Momentary dipole. Weaker than formal dipole. Becomes significant for larger molecules

Between momentary dipoles

Question 7

Order of intermolecular force strength

Answer 7

Ion-Ion > Ion-dipole > H bond > Dipole-dipole > Dispersion

Question 8

Electrostatic interactions

Answer 8

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

Question 9

Condensation

Answer 9

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

Question 10

Change in temperature

Answer 10

Results in change in kinetic energy, which makes the molecules stick together more or less efficiently

Question 11

Comparing interactions

Answer 11

1. Which is the strongest type of interaction each substance can do? (i.e. H-bonds vs dispersion)
2. 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.

Question 12

Melting point determination

Answer 12

More branching in a molecule = more compact = ‘higher’ melting point

More linear = less compact = weaker interactions = ‘lower’ melting point

Question 13

Crystalline solids

Answer 13

Have a repeating lattice structure.

Can be categorized as molecular solids, network solids, ionic solids or metallic solids

Question 14

Molecular solids

Answer 14

A type of crystalline solid

The solid phase for small molecules. (i.e. water freezes to ice). Lowest melting and boiling points

Question 15

Network solids

Answer 15

A type of crystalline solid

Covalently bonding throughout the solid.

Ex. diamond, quartz

Question 16

Ionic solids

Answer 16

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

Question 17

Metallic solids

Answer 17

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

Question 18

Amorphous solids

Answer 18

no repeating lattice structure, because the molecular is large and do not have organization

glass, polymers, gels

Question 19

Simple cubic cell

Answer 19

A type of unit cell. Part of ionic solids.

1 atom/unit cell. 1/8th of an atom at each corner

Question 20

Face-centered cubic cell

Answer 20

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

Question 21

Body-centered cubic cell

Answer 21

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

Question 22

Phase changes

Answer 22

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.

Question 23

Phase diagrams

Answer 23

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

Question 24

Lines on phase diagram

Answer 24

Indicate equilibria between 2 phases

Question 25

Triple point

Answer 25

On phase diagram. Is when there is an equilibrium between all 3 phases

Question 26

Supercritical fluid; critical point

Answer 26

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

Question 27

Vapour pressure

Answer 27

Vapour pressure is a measure of the tendency of a material to change into the gaseous or vapour state, and it increases with temperature