This question is about potassium and zinc - Edexcel - GCSE Chemistry Combined Science - Question 3 - 2021 - Paper 1

Potassium has the atomic number 19, which means it has 19 electrons. The electronic configuration of potassium is represented as

$1s^2 2s^2 2p^6 3s^1$

This configuration shows that potassium has one electron in its outermost shell (3s). In the periodic table, the position is determined by the number of valence electrons. Potassium is in Group 1 (the alkali metals), indicating it has one valence electron. Atoms in the same group have similar chemical properties due to their similar electronic configurations, primarily concerning their outermost electrons.

To demonstrate that a gas is oxygen, a glowing splint can be used. The glowing splint is introduced into a sample of gas; if it relights, this indicates the presence of oxygen, as oxygen supports combustion.

The electronic configuration for potassium (K) is

$[Ar] 4s^1$

When potassium forms an ion, it loses one electron to achieve a noble gas configuration:

$K^+ : [Ar]$

The oxide ion (O) has the electronic configuration:

$O^{2-} : [He] 2s^2 2p^6$

Thus, the formula for potassium oxide is K₂O, indicating that two potassium ions are needed for every oxide ion.