Question

Why ionization energy decreases down the group and increases along a period?

Answer 1

The ionisation energy is the energy required to remove electrons from the outer most shells of the electron is called ionisation energy.

It decreases down the group because -

-As we move down the group the size of the elements increases

-The distance between the nucleus and the outer most electron also increases.

-This leads to a decreased force of attraction between the nucleus and it becomes easier to remove them.

Similarly when we move across the period the number of electrons in the same shell increases which leads to strong forces of attraction and the ionisation energy increases.