Question

How does ionization energy vary across a period and down the group?

Answer 1

Ionization energy: Ionization energy is the amount of energy required to remove the outermost electron from a specific isolated gaseous atom or ion. It is estimated in KJ/mol.

Trend of Ionisation energy along Period and group:

• Ionization energy increases across a period (on moving left to right) and decreases (on moving up to down) down the group.
• As we move across a period, the atomic radii decrease, and the effective nuclear charge increases. So, the external electrons are held nearer to the nucleus and all the more emphatically pulled into the middle. Thus, it becomes harder to remove an electron from the atom. Hence, more ionization energy is required.
• As we move down the group, the atomic size increases and effective nuclear charge decreases as the outermost electrons are further away from nucleus. Thus, it becomes easy to remove an electron from the atom. Hence, less ionization energy is required.