3.2.1 Classification

Question 1

What is the meaning of periodicity?

Answer 1

Pattern in the change of properties in a row of a elements which is repeated in the following rows as well.

Question 2

What are the different blocks in the period table?

Answer 2

s, p, d, f

Question 3

Describe and explain the trend in atomic radius across a period.

Answer 3

L to R: atomic radius decreases
- Nuclear charge increases
- Shielding is similar
- Stronger attraction between electron shells and nucleus

Question 4

Describe and explain the trend in first ionisation energy across a period.

Answer 4

L to R: general increase in 1st IE
- Nuclear charge increases
- Shielding similar
- Atomic radius decreases

Exceptions:
- between group 2&3 (s→p orbital)
- between group 5&6 (electron repulsions)

Question 5

Describe and expalin the trend in melting points across period 3 (Na→Ar).

Answer 5

Na→Al : increase
stronger metallic bonds due to increased ion charge and smaller ionic radius

Al→Si : increase
Si has giant covalent bonding (many strong covalent bonds)

Si→P : decrease
P4 is simple covalent bonding (IMFs)

P→S : increase
P4 < S8, larger molecule, stronger Van der Waals’

S→Ar : decrease
Cl2 is a smaller molecule, Ar is monatomic, weaker Van der Waals’

Question 6

In terms of structure and bonding, explain why sulfur has a higher melting point than phosphorus.

Answer 6

• S8 is a larger molecule than P4
• Stronger Van der Waals’ forces between the molecules of S8
• Requires more energy to overcome than in P4

Question 7

In terms of atomic structure, explain why the Van der Waals’ forces in liquid argon are very weak.

Answer 7

• Argon is monatomic, single atom with few electrons
• Electrons are closer to the nucleus, strong attraction
• Atom’s electrons can’t easily be polarised