From the following elements: ₄Be; ₉F; ₁₉K; ₂₀Ca

(i) Select the element having one electron in the outermost shell.

(ii) Two elements of the same group.

Write the formula of and mention the nature of the compound formed by the union of ₁₉K and element X (2,8,7).

(i) ₁₉K electronic configuration = 2,8,8,1

Thus potassium has 1 valance electron in outermost shell.

(ii) ₄Be, ₂₀Ca belong to the same group.

Reason- Be configuration 2,2

Ca configuration 2,8,8,2

Both have same number of valance electrons (2) in the outermost shell hence will belong to same group i.e. group 2.

Electronic configuration of element X is 2, 8, 7

Number of valence electrons in X = 7

Valency of X = 8 − 7 = 1

Atomic number of K = 19 Electronic configuration of K is 2, 8, 8, 1.

Number of valence electrons in K = 1 Valency of K = 1

Therefore, the formula of the compound formed when K and element X combine is KX. The compound KX is of ionic nature.