Ionisation energy is defined as the energy required to remove the most loosely bound electron from an isolated gaseous atom. Key factors influencing ionisation energy include atomic size, the charge on the atom, and the effectiveness of inner electron shells in screening nuclear charge. The periodic trend shows that ionisation energy decreases down a group and increases across a period.

1. Ionisation Energy
Dr. Mithil Fal Desai
Shree Mallikarjun and Shri Chetan Manju Desai College
Canacona Goa

2. e-
e-
e-
e-
Ionisation energy
+
Amount of energy required to remove the most loosely bound electron
from an isolated gaseous atom
I. E.1

3. e-
e-
e-
e-
Second ionisation energy
+
I. E.1
+ +I. E.2

4. Periodic trend in Ionisation energy

5. Factors affecting Ionisation energy
• Size of atom
• The charge on atom
• How effectively inner electron shell screen
the nuclear charge
• Type of electron

6. I. E.1< I. E.2<I.E.3
Atomic number increases
• I.E. decreases down the group
• I.E. increases along the row
Ionisation energy