Periodicity

Question 1

Describe atomic radius trends..

Answer 1

ACROSS THE PERIODS:

Atomic radii decrease from left to right across a
period, because the increased number of protons
create more positive charge attraction for electrons
which are in the same shell with similar shielding

DOWN GROUPS:

Atomic radius increases down group due to extra electron shells added.

Question 2

Describe Melting point trends in period 3?

Answer 2

Sodium + magnesium+ aluminium

-all undergo metallic bonding as they are metals. As you go along there is a general increase in melting point as metal ions have an increasing positive charge. This means a stronger metallic bond.

SILICON
- has highest melting point

This is due to its giant covalent bonding. Many strong covalent bonds hold silicon atoms together and loads of energy are needed to overcome these strong covalent bonds.

PHOSPHORUS (P4)

This is due to its simple molecular formula structure. MP determined by VDW forces.

SULFUR(S8)

slightly bigger molecule then phosphorus so has larger VDW forces and so higher melting point.

CHLORINE

It has smaller VDW forces

ARGON

it only exists as an individual atom so has even smaller VDW forces so low melting point.

Question 3

Ionisation energy meaning..

Answer 3

lonisation energy is the minimum amount of energy required to remove 1 mole of electrons from 1 mole of atoms in the gaseous state

Question 4

what is successive ionisation?

Answer 4

Removal of more than 1 electron from the same atom.

Question 5

What is 1st ionisation energy trends down a group?

Answer 5

Decreases down groups.
Atomic radius increases as we go down the group. Outer electrons are further from the nucleus. Force of attraction between outer electron and nucleus is weaker. So energy required to remove an electron decreases.

shielding also increases weakening attractive force.

Question 6

What is 1st ionisation energy trends across a period?

Answer 6

The increasing number of protons this increases nuclear attraction.

shielding remains the same.

Question 7

What are the exceptions to usual ionisation trends in period 3?

Answer 7

Aluminium + Magnesium:

The outer most electron in Aluminium sits in a higher energy sub-shell slightly further from the nucleus than the outer electron in Magnesium. (not supported by Neils Bohr theory)

Phosphorus and sulfur:

Phosphorous and Sulfur both have outer electrons in the 3p orbital so the shielding is the same.

Removing an electron from Sulfur involves taking it from an orbital with 2 electrons in , due to electron repulsion less energy is needed to remove an electron from an orbital with 2 electrons than one.