Unit 1 - Past Paper Questions

Question 1

Explain why the covalent radius of sulfur is smaller than that of phosphorous. (1)

Answer 1

Increased nuclear attraction for electrons/increased nuclear charge/sulfur has more protons in the nucleus.

0 marks would be given for increased attaction of electrons for nucleus.

Question 2

Explain why covalent radius decreases across the period from sodium to chlorine. (1)

Answer 2

Electron shells are pulled closer because nuclear charge incrases/the number of the protons in the nucleus increases.

Must mention nuclear charge or no. of protons in answers giving the idea of pull by the nucleus. Increased nuclear pull is not accepted

Question 3

Explain fully why the covalent radius of sodium is larger than the ionic radius of sodium. (2)

Answer 3

Must make 2 points:
- understanding that the atom loses an electron (when the ion is formed). 1 mark.

• the sodium ion will only have two electron shells whereas the sodium atom has 3 electron shells OR the sodium ion will have fewer electron shells than the atom. 1 mark.

Diagram of the atom and ion would give 1 mark but explanation required for the full 2

Question 4

Explain why the first ionisation energy decreases going down Group 1. (1)

Answer 4

As you go down the group the outer electron is more shilded from the nuclear pull OR less strongly attracted by the nucleus.

Question 5

Explain fully why the second ionisation energy is much greater than the first ionisation energy for Group 1 elements. (2)

Answer 5

2nd ionisation energy involves removal from an electron shell which is innter/full/stable/closer to the nucleus

OR
second electron is removed from an electron shell which is full/stable/closer to the nucleus (1 mark)

the electron is less shielded from, or more strongly attacted to the nucleus. (1 mark)

Stating that more enrgy is required to remove the second electron would be seen as restating the information from the stem.

Question 6

The melting point of sulfur is much higher than that of phosphorus. Explain fully in terms of the structures of sulfur and phosphorus molecules and teh intermolecular foces between molecules of each element, why the melting point of sulfur is much higher than that of phosphorus. (3)

Answer 6

1 mark - correctly identify that the forces are stronger between sulfur than between the phosphorus molecules.

1 mark - Correctly identifying that there are London dispersion forces between the moecules of both these elements.

1 mark - these forces are stronger due to sulfur structure being S8 whereas phosphorus is P4.

Key points - Must mention S8 and P4 for the 3rd mark (this is an A mark)

Question 7

Explain why covalent radius decreases across the period from sodium to chlorine. (1)

Answer 7

(the electron shells are pulled closer because) nuclear charge increases/the number of protons in the nucleus increases.

mention must be made of nuclear charge or number of protons in the answer giving the idea of pull by the nucleus. Increased nuclear pull is not accepted

Question 8

Name the element from the 3rd period that exists as a covalent network.

Choices: Na, Mg, Al, Si, P, S, Cl, Ar (1)

Answer 8

Silicon. Symbol also accepted.

Question 9

Ionistaion energy changes across the period. Explain why the first ionisation energy increases across the period. (1)

Answer 9

Increasing/greater/stronger/higher nuclear charge

OR

Increasing number of protons.

Increased nuclear pull on its own not accepted. Muention must be made of nuclear charge or number of protons

Question 10

Write an equation, including state symbols, for the second ionisation energy of magnesium. (1)

Answer 10

Mg+ (g) –> Mg2+ (g) + e-

State symbols required

Question 11

Below you’ll see the first four ionisation energies for aluminium.

1st - 578 kJ
2nd - 1817kJ
3rd - 2745kJ
4th - 11577kJ

Explain why there is a large difference between the third and fourth ionisation energies. (1)

Answer 11

Fourth ioinsation energy involves the removeal of an electron from an electron shell which is inner/full/more stable/closer to the nucleus.

Lots of other ways to word this but all saying roughly the same thing.

Question 12

The boiling point of chlorine is much higher than that of argon.
Explain fully, in terms of structure and the type of van der Waals forces present, why the boiling point of chlorine is higher than that of argon. (3)

Answer 12

1 mark - correctly identify that there are stronger/more(Van der waals) forces between chlorine molcules than between argon atoms.

1 mark - correctly identifying that the van der Waals forces present in both these elements are LDFs.

1 mark - Chlorine molecules (Cl2)have more electrons than argon atoms (Ar).