Question

Explain:
(i) Larger the atomic size, more metallic is the element.
(ii) Halogens have high electron affinity.
(iii) Size of atom changes when it loses or gain electron.
(iv) K is more reactive than Li.
(v) Electronegativity of Cl is higher than S.
(vi) Group 17 elements are non-metals, while group 1 elements are metals.

Answer 1

(i) The larger the atomic size of the element, the larger will be the distance between the nucleus (carrying positive charge) and valence electrons. Losing an electron would be more easy due to lesser attraction between the nucleus and the outermost electron. Hence, the element will show greater metallic character.

(ii) Halogens have seven electrons in their valence shell. They need only one electron to complete their octet. Hence, they have a high tendency to accept electron and form an anion to complete their octet. Hence, they have large value of electron affinity.

(iii) When an atom loses an electron, there is no change in nuclear charge of the atom but the number of negatively charged electrons decreases. Hence, nucleus attracts the electrons more tightly, which decreases the size of the ion. When an atom gains an electron, there is one extra electron in the valence shell due to which nucleus exerts less force on outermost electrons and this results in the increase in atomic radius. Hence, the size of the atom changes when it loses or gains electron.

(iv) As we move down in the first group, more shells are added due to which attraction between the nucleus and valence electron decreases. The lesser the attraction between the nucleus and valence electron, the lesser will be the ionisation energy and the greater will be the reactivity of the element. Hence, K is more reactive than Li.

(v) As we move towards right in the periodic table, electronegativity increases. Hence, chlorine has higher electronegativity than sulphur.

(vi) Group 17 elements are non-metals because they lack only one electron to attain noble gas configuration. So, these elements have high tendency to gain electrons due to which they show non-metallic character. Group 1 elements have only one electron in their valence shell due to which they have a high tendency to lose this electron and attain noble gas configuration. Hence, they show metallic behaviour.