Question

why the ionisation Energy of an atom increases across the period?

Answer 1

Hello friend!!
Rajdeep here..

Ionisation Energy is the energy required to remove an electron from an atom in its isolated gaseous state.
As we move from left to right across a period, number of shells remain the same but number of valence electrons increase by one.

Hence, the nuclear pull on the valence electrons gradually increases, due to which you will need MORE ENERGY (I.e., you have to spend more energy and do more work) to remove an electron from that very atom.
So, Ionization energy increases across the period.

Hope you understand...
You need a clear concept of the periodic table to understand these....

Thanks!!

Answer 2

due to decrease in atomic radii of atons,ionisation energy increases on moving from left to write in the pt. distance between nucleus and outermost electons decreases,large amount of energy is required