8.Periodicty

Question 1

Name all the blocks in the periodic table

Answer 1

s, p, d and f

Question 2

How are elements classified into blocks

Answer 2

The elements highest energy electron determines the block, by the orbital it is in. For example if it is in the s orbital it is in the s block

Question 3

Describe and explain the trend of atomic radii across a period

Answer 3

Atomic radii decrease due to increased nuclear attraction with no increased shielding

Question 4

Describe and explain the trend of atomic radii down a group

Answer 4

Atomic radii increase going down a group due to decreased nuclear attraction because of increased shielding so

Question 5

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

Answer 5

Increases across a period as it requires more energy to get rid of an electron as the nuclear attraction increases due to an increase of nuclear charge

Question 6

Describe and explain the trend in first ionisation energy down a group

Answer 6

Decreases down a group due to decreased nuclear attraction because of increased shielding. It requires less energy to remove an electron

Question 7

Why is there a drop in first ionisation energies between groups 2&3 and 5&6 across a period

Answer 7

• in group 3 the first electron is in a higher electron level meaning there is more shielding so less nuclear attraction compared to group 2’s first electron. Requires less energy to remove
• in group 5 all electrons in the p orbital are not paired whereas in group 6 one is paired. The repulsion between these paired electrons means less energy is needed to remove it

Question 8

Describe and explain the trend in melting points across period 3

Answer 8

Giant structures (left) have high melting points whereas molecular structures (right) have lower boiling points. Molecular structures m.p depends on how packed the electrons are (Van der Waal forces). For this reason S8>P4>Cl2. Si is a giant molecular structure so significantly higher.