Periodicity

Question 1

What makes an element be in the s, d or p block of the periodic table?

Answer 1

Its outer electron would be in the corresponding block.

Question 2

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

Answer 2

Outer electrons in same shell
More protons in nucleus.
Same amount of shielding.
So stronger attraction between the nucleus and the outer shell electrons.
So these outer shell electrons are pulled closer towards the nucleus resulting in a smaller atomic radius.

Question 3

Describe and explain the trend in atomic radius as you go down a group.

Answer 3

More shells.
Greater distance between the nucleus and the outer shell electrons.
Increased amount of shielding.
So weaker attraction between the nucleus and the outer shell electrons
So the outer shell electrons are further away from the nucleus which results in a bigger atomic radius.

Question 4

Describe and explain the general trend for 1st ionisation energies across a period.

Answer 4

Increases.
More protons.
Atoms get smaller.
Stronger attraction between the nucleus and outer electrons = more energy required to remove the outer electron/s

Question 5

Define electronegativity.

Answer 5

Electronegativity is a measure of the tendency of an atom to attract a ponding pair of electrons in a covalent bond.

Question 6

Describe and explain the trend of electronegativity as you go across a period.

Answer 6

Increases.
As you go across a period the number of protons in the nucleus increases and the atomic radius decreases so there is a stronger attraction between the nucleus and the 2 electrons in a covalent bond.

Question 7

Describe the trend in melting points in period 3 elements.

Answer 7

Increase from sodium to silicon then generally decrease from silicon to argon.

Question 8

Explain the increase in melting pts from sodium to silicon

Answer 8

Increasing from Na-Si as Na, Mg, and Al all have metal-metal bonds and ∴ a strong force of attraction between + metal ions & delocalised electrons. Is increasing as you go across because there is a higher charge (^ protons) & ^ delocalised electrons & a smaller ion so the bonds get stronger. Si is macromolecular and has many strong covalent bonds so a lot of energy is needed to break these bonds.

Question 9

Explain the decrease in melting pts from silicon to argon

Answer 9

P, S & Cl are held together by Van der Waal’s forces which are weak & ∴ easier to overcome S8>P4>Cl2 = bigger molecules, more electrons, more VdW then Ar is monoatomic resulting in very weak Van der Waals forces to overcome