Question

Define ionisation enthalpy. How does it varies along a period and down the group in the periodic table.

Answer 1

Ionisation enthalpy- The energy that is provided to an isolated gaseous atom to extract one outer valance shell electron.

• In Groups
  

It is easy to extract when electron loosely bound to nucleus that's why in groups, the ionisation enthalpy decreases,

• In Periods

$Ionisationenthalpy\propto Zeff.$

As the Z effective increase in a period that's why ionisation enthalpy increases.

$Zeffective=effectiveatomicnumber$