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.

Why same-group elements react alike

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)

Exam tip

Why elements in the same group have similar chemical properties

What comes up: explain why two elements in the same group (e.g. lithium and sodium, or chlorine and bromine) have similar reactions.

Write: they have the same number of electrons in their outer shell (e.g. both have 1 outer-shell electron), so their chemical behaviour is the same.

Watch out: "same number of protons" scores zero — proton count differs between group members; it is the outer-electron count that is identical. The mark scheme also allows "same number of valence electrons" as an alternative phrasing.

Trends in reactivity down a group

1 (): 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 (): 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 noble gases (Group 0)

The Group 0 elements are called the
Common properties:

Exam tip

Why noble gases do not react

What comes up: explain, in terms of electron configuration, why a noble gas such as neon or argon is unreactive (commonly 2 marks; occasionally 1 mark as "state why").

Write (two marks): (1) Its outer shell is full (neon: 2,8; argon: 2,8,8 — 8 electrons in the outer shell). (2) It therefore has no need to lose, gain, or share electrons.

Watch out: for a 1-mark "state" question, either mark point alone is accepted — but for the 2-mark "explain" version both points are needed. Do not write "noble gases are metals" or confuse Group 0 with Group 8; the mark scheme says IGNORE references to "noble gas" as a reason on its own.

Noble-gas electronic configurations

Noble gas	Z	Electronic configuration
Helium (He)	2	2
Neon (Ne)	10	2,8
Argon (Ar)	18	2,8,8
Krypton (Kr)	36