3.1-3.2

Question 1

Molecular compounds boil at ____ temperatures than ionic compounds

Answer 1

lower

Question 2

Lattice energy

Answer 2

Energy required to completely separate one mole of a solid ionic compound into gaseous ions
… measure of the stability of any ionic solid

Question 3

Born-Haber cycle

Answer 3

Relates lattice energies of ionic compounds to ionization energies, electron affinities, and other atomic and molecular properties
… defines various steps that precede formation of an ionic solid

Question 4

Bond enthalpy

Answer 4

Energy required to break a covalent bond

Question 5

Born-Harbor cycle for LiF
Li(s) + 1/2(F_2) –> LiF (s)

Answer 5

(1) Convert solid lithium to lithium vapor (+H) (sublimation)
(2) Dissociate 1/2 mole of F_2 gas into separate gaseous F atoms (+H)
(3) Ionize 1 mole of gaseous Li atoms (+H)
(4) Add 1 mole of electrons to 1 mole of gaseous F atoms (-H)
(5) Combine 1 mole of gaseous Li+ and 1 mole of F- to form 1 mole of solid LiF (-H)

Question 6

Why is lattice energy always positive?

Answer 6

Separation of ions in a solid into ions in the gas phase is an endothermic process, so the larger the lattice energy, the more stable the solid and more tightly held the ions

Question 7

Why…
does MgCl_2 exist and not MgCl?
does NaCl exist and not NaCl_2?

Answer 7

Must balance between ionization energies and the stability, or lattice energy, from the formation of the solid

Question 8

4 types of crystals

Answer 8

Ionic, covalent, molecular, metallic

Question 9

Two important characteristics of ionic solids

Answer 9

(1) Composed of charged species
(2) Anions and cations are generally quite different in size

Question 10

When do ionic solids conduct electricity?

Answer 10

Not in the solid state, because strong cohesive forces fix the ions in place.
In the molten state or dissolved in water, the ions are free to move and conduct electricity.

Question 11

Why is diamond hard?

Answer 11

Each carbon is sp^3 hybridized, resulting in a very strong tetrahedral structure with a high melting point.

Question 12

What holds covalent crystals together?

Answer 12

An extensive 3-D network of covalent bonds

Question 13

Why is graphite a good conductor of electricity?

Answer 13

Carbon is arranged in six-membered rings, sp^2 hybridized, with the unhybridized 2p obital used in pi bonding. This delocalized molecular orbital allows electrons to move around. (covalent bonds = hard, layers of carbon rings can slide = lubricant, slippery)

Question 14

Describe molecular crystals

Answer 14

Lattice points are occupied by molecules, and the attractive force that holds them together are van der Waals forces and/or hydrogen bonding
Soft, low melting point, poor conductor

Question 15

Describe metallic crystals

Answer 15

Every lattice points is occupied by an atom of the same metal
Bonding is delocalized over the entire crystal, delocalized electrons make metals good conductors

Question 16

van der Waals forces

Answer 16

Dipole-dipole, dipole-induced dipole, dispersion forces

Question 17

Dipole-dipole forces

Answer 17

Attractive forces between molecules that possess dipole moments

Question 18

Ion-dipole forces

Answer 18

Attract an ion and a polar molecule to each other

Question 19

Induced dipole (from an ion or dipole)

Answer 19

Separation of positive and negative charges in the non polar molecule is due to the proximity of an ion or a polar molecule

Question 20

Polarizability

Answer 20

Ease with which electron distribution in the atom can be distorted

Question 21

Dispersion forces

Answer 21

Attractive forces that arise as a result of temporary dipoles induced in atoms or molecules

Question 22

Hydrogen bond

Answer 22

Dipole-dipole interaction between hydrogen atom in a polar bond and an electronegative O, N, or F atom