Periodicity

Question 1

How is an element classified as s, p, d, or f block?

Answer 1

According to its position in the periodic table, which is their proton number.

Question 2

Describe and explain the trend in atomic radius across period 3.

Answer 2

Atomic radius decreases.
Increase in nuclear charge for the same number if electron shells. The outer electrons are pulled in closed to the nucleus as increased charge causes greater attraction.

Question 3

Describe and explain the change in first ionisation energy across period 3.

Answer 3

Along a period, ionisation energy increased.
The decreasing atomic radius and increasing nuclear charge means the outer electrons are held more strongly and therefore more energy is required to remove the outer electron to ionise the atom.

Question 4

Describe the trend in melting point along period 3.

Answer 4

Increased from Na to Si, then decreases from Si to Ar.

Question 5

Why do Sodium, magnesium and aluminium have high melting points?

Answer 5

They are metals with metallic bonding.
Their melting points increase due to greater positive charged ions. This also means more electrons are released as free electrons so electrostatic force of attraction between the positive ions and negatively charged electrons increases from Na to Al

Question 6

Why does Silicon have a high melting point?

Answer 6

Silicon is macromolecular, meaning it has a very strong covalent structure. These covalent bonds require a lot of energy to break giving it a high melting point.

Question 7

Why do phosphorus, sulphur, and chlorine have lower melting points?

Answer 7

They are all simple covalent molecules, held by weak Can ser Waals forces. These intermolecular forces do not require much energy to overcome, so they have relatively low melting points.

Question 8

State the meaning of first ionization energy of an atom.

Answer 8

The amount of energy needed to remove one outermost electron from a gaseous ion.

Question 9

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

Answer 9

Sulfur molecules are larger than phosphorus molecules.
Therefore, Van der Waal’s forces between molecules are stronger.
Therefore, mor energy needed to loosen forces between molecules.

Question 10

Describe and explain the trend in first ionization energy across period 2.

Answer 10

Stage 1: General Trend (Li → Ne)
1a.1st IE increases
1b.More protons/increased
nuclear charge
1c.Electrons in same energy level
/ shell
1d.No extra/similar shielding
1e.Stronger attraction between nucleus and outer e OR outer e closer to nucleus (ignore radius decreases)

Stage 2: Deviation Be → B

2a. B lower than Be
2b. Outer electron in (2)p
2c. higher in energy than (2)s

Stage 3: Deviation N → O

3a. O lower than N
3b. 2 electrons in (2)p need to pair
3c. pairing causes repulsion (do not award if it is clear reference to repulsion is in s orbital)