Group Reactivity and the Noble Gases — The Periodic Table | IGCSE Chemistry

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 8% of your exam marks.

stable

Low

Stable8%

Group trends, periods and atomic radius/ionisation energy are regularly examined.

Elements in the same group all have the same number of outer-shell electrons
Chemical behaviour is set almost entirely by the outer electrons
So same-group elements:
- Form the same kinds of bonds
- React with the same other elements
- Show similar chemical reactions
For example, lithium, sodium and potassium are all in Group 1 and all react with chlorine (Group 7) to form ionic chlorides (LiCl, NaCl, KCl)

Group 1 (alkali metals): reactivity increases going down the group
- The outer electron is held more loosely the further it sits from the nucleus, so it is lost more easily
Group 7 (halogens): reactivity decreases going down the group
- The outer shell sits further from the nucleus, so an incoming electron is attracted less strongly
The detailed chemistry of these groups is in Topic 10 (Group 1) and Topic 11 (Group 7)

The Group 0 elements are called the noble gases
Common properties:
- Non-metals
- Monatomic (exist as single atoms, not bonded into molecules)
- Colourless gases at room temperature
- Non-flammable
They are inert (extremely unreactive)
- Most elements react in order to gain, lose or share electrons until they have a full outer shell
- Noble gases already have a full outer shell, so they have no chemical incentive to react
Outer-shell electrons:
- Helium has 2 (a full 1st shell)
- All other noble gases have 8 outer electrons

From krypton onwards the third shell holds its full 18 electrons (the simplified IGCSE rule applies only to the first 20 elements)