✨Module 3: Periodicity

Question 1

The more atoms in a molecule …

Answer 1

The stronger the London forces so higher b.m.p.

Question 2

The higher the charge of an ion in an ionic compound …

Answer 2

The stronger the London forces so higher b.m.p.

Question 3

Why does bromine have a low b.m.p?

Answer 3

Simple molecular with weak London forces BETWEEN molecules, which don’t require much energy to break.

Question 4

Metallic and ionic bonds are stronger than …

Answer 4

London forces.

Question 5

Why does Ba have a low ionisation energy?

Answer 5

Increased distance/shielding outweighs increased nuclear charge.

Question 6

Why does strontium metal have a high b.m.p?

Answer 6

It’s a giant metallic lattice with a regular arrangement of positive ions in a sea of delocalised electrons. Very strong forces between electrons and cations that require a lot of energy to break.

Question 7

Define first ionisation energy.

Answer 7

Energy required to remove 1 electron from each atom in one mole of GASEOUS atoms to form one mole of GASEOUS 1+ ions.

Question 8

3 factors that affect the ionisation energy.

Answer 8

Atomic radius - larger the distance between nucleus and outer electron, the lower the ionisation energy.
Nuclear charge - the more protons in the nucleus, the greater the attraction between nucleus and outer electron so bigger ionisation energy.
Electron shielding - inner shell electrons repel outer electrons so reduced ionisation energy as less nuclear attraction

Question 9

Define second ionisation energy.

Answer 9

Energy required to remove 1 electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions.

Question 10

Explain why the second ionisation energy of Helium is more than the first ionisation energy of helium.

Answer 10

After the first electron is lost, the single second electron is pulled closer to the nucleus as the number of protons don’t change (more + charge attracts the electron). Stronger nuclear attraction on remaining electron so more energy needed to remove it.

Question 11

Mercury is the only metal that is a …

Answer 11

Liquid at room temp.

Question 12

Define metallic bonding.

Answer 12

Strong electrostatic force of attraction between cations and delocalised electrons.
Cations are fixed in position, maintaining shape of metal.
Delocalised electrons can move throughout the structure.

Question 13

Describe 3 factors that affect the strength of metallic bonding.

Answer 13

1. No. protons - more protons mean stronger bonds.
2. No. delocalised electrons per atom - more delocalised electrons mean stronger bonds.
3. Size of ion - the smaller the ion, stronger the bond.

Question 14

Explain why Mg has stronger metallic bonding that Na and therefore a higher b.m.p.

Answer 14

In Mg, there are more electrons in their outer shell that gets released to the sea of electrons. Mg ion is also smaller as it has one more proton. So stronger electrostatic attraction between positive metal ions and delocalised electrons and higher energy is needed to break the bonds.

Question 15

Metals also …

Answer 15

Conduct electricity due to delocalised electrons that can move, and metals aren’t soluble.

Question 16

Why do giant covalent substances have high b.m.p?

Answer 16

Many strong covalent bonds that require a large amount of energy to break.

Question 17

Why don’t giant covalent substances conduct electricity?

Answer 17

Electrons can’t move. But in graphite, each carbon has one delocalised electron tat can move.

Question 18

Why are metals malleable?

Answer 18

Layers of positive ions can slide over each other

Question 19

Giant covalent substances are also …

Answer 19

Insoluble.

Question 20

Why is there a sharp decrease in melting point across period 2 + 3 between group 14 and group 15?

Answer 20

It marks a change from giant to simple molecular substances. Simple molecular substances like S8, P4, Cl2 have weak London forces between molecules, ,so little energy required to break them.
Ar is monatomic so weak London forces between ATOMS.