CHE - Covalent Bonding

Question 1

What are the useful properties of graphite?

Answer 1

Conducts electricity in solid state
Soft greasy nature
High melting temperature
Grey opaque solid

Question 2

What is sublimation?

Answer 2

Ability to go from solid to gas (bypass liquid)

Question 3

Describe the basics of covalent bonds (electron behaviour, elements)

Answer 3

Electrons shared

Non-metals only

Question 4

What is covalency?

Answer 4

The number of electrons it shares when bonding covalently (not rule b/c some elements form multiple different molecules with that same non-metal eg SO2 and SO3)

Eg Cl2 has covalency of one (single bond)

Question 5

What are the classic examples of each of the valence structure shapes?

Answer 5

Linear: CO2 (carbon dioxide)
V-shaped / angular: H2O (water)
Pyramidal / triangular pyramid: NH3 (ammonia)
Tetrahedral: CH4 (methane)
Planar triangle: BF3
Octahedral: SF6

Question 6

What determines where an electron spends more time in a covalent bond?

Answer 6

Electronegativity (higher = more time = slightly negative > polarised bond)

> two dipoles (molecule = a dipole and polar)

Question 7

What are the three types of intermolecular forces and when do they apply?

Answer 7

Dispersion forces > non-polar molecules
Dipole-dipole interaction/attraction > polar molecules (opposite ends of molecules line up)
Hydrogen bonds > polar molecules where H is bonded w/ N, O, or F

Question 8

How do you determine polarity of molecules?

Answer 8

Pos and neg ends > dipole > ASYMMETRICAL > polar

Neg ends only or pos ends only > SYMMETRICAL > non-polar

Question 9

Why does hydrogen bonding occur?

Answer 9

N, O, F are highly electronegative > highly polarised bonds > large positive charge on H > N, O, F have at least one lone pair of electrons when they form molecules > H of one molecule bonds w/ lone pair of F, N, or O atom of other molecule

Question 10

What is the weakest bonding force (dispersion forces)?

Answer 10

Operates in all substances, only considered when only one (for non-polar molecules)

Arises out of constant movement of electrons in atoms and molecules
At one moment, more electrons at one side than other > momentarily polar > electrostatically interact w/ atoms or molecules > direction of instantaneous interactions are always changing > instantaneous dipole > net, but weak, force of attraction b/w all particle

Only force for noble gases in l and s states, and have low melt/boil temps (increase as atom size increases)

Question 11

What is a semistructural formula (eg of butane)?

Answer 11

Eg of butane: CH3CH2CH2CH3

Question 12

What is an allotrope? Name three allotropes of carbon.

Answer 12

Different physical forms of the same element

1. Diamond
2. Charcoal
3. Graphite