Question

Going down in a group from fluorine to iodine, which of the following properties decreases?
A) Ionic radius
B) Ionisation energy
C) Oxidising power
D) Electronegativity.

Answer 1

Hint:As we know that ionic radius is the distance between the centre of nucleus to electron in the last orbit of an ion. Ionisation energy is the minimum amount of the energy supplied to remove an electron and electronegativity is the tendency of an atom to attract the shared pair of electrons.


Complete solution:
As we know that every chemical element and every group of the periodic table possess some similar chemical properties. Group 17 elements or halogens possess some of these similar chemical properties and follow the trends like the other groups. Let us talk about these properties one by one.
First is the ionic radius which is basically the distance between the centre of the nucleus of an ion and the electron in the outermost shell of the ion. Also, the cation is smaller than the parent atom due to large effective nuclear charge and the anion is larger than the parent atom due to low effective nuclear charge. As we move down the group, ionic radius increases as the size increases and new shells are added. Thus it is not a correct answer.
Now, we have Ionisation energy which is the amount of energy which should be supplied to an atom to remove an electron from an isolated gaseous atom to form a gaseous cation. It decreases down the group because the size increases which decreases the attraction of valence electrons and the nucleus and thus a small amount of energy is required to remove that valence shell electron.
Next we have oxidising power which is the power of an atom to accept an electron from another atom and itself gets reduced is the oxidising power of that atom. It also decreases down the group.
Lastly, the electronegativity which is the tendency of an atom that can attract the shared electron pair towards itself and it also decreases down the group like ionisation energy due to increase in size of the atom.

Therefore, from the above explanation we can say that the correct options are (B),(C),(D).


Note:Remember that when elements have low ionisation energy, it means it has the greater reducing power, electropositivity and basic characters. And greater the value of positive charge on an atom, smaller will be the size and greater the charge on an anion, larger will be the size of the atom.