Question

Why is the first ionization enthalpy of chromium lower than that of zinc?

Answer 1

In basic words, ionisation energy is a measure of how difficult it is to remove an electron from an atom or ion, or how likely an atom or ion is to yield an electron. The loss of one electron generally occurs in the chemical species' ground state. We may also say that ionisation, or ionisation energy, is a measure of the strength (attractive forces) with which an electron is held in place.

Complete answer:
It is usually more difficult to remove one electron when the ionisation energy is large. The attraction forces are also governed by a number of variables.
The electrons are strongly attracted to the nucleus if it is positively charged.
When an electron is close to or near the nucleus, the attraction is stronger than when the electron is further away.
The attraction forces between the outer level and the nucleus are reduced when there are more electrons between them.
When two electrons are in the same orbital, they repel each other in some way. The nucleus' attraction is now disrupted as a result of this.

Element	Atomic number	Electronic configuration
Chromium	24	$[Ar]4{{s}^{1}}3{{d}^{5}}$
Zinc	30	$[Ar]4{{s}^{2}}3{{d}^{10}}$

The enthalpy of chromium's initial ionisation is lower than that of zinc.
To get the more stable half-filled form in Cr, the initial electron must be readily withdrawn from the 4s orbital. As a result, Cr's ionisation enthalpy is smaller.
However, in the case of Zinc, this is not the case.
It gets increasingly difficult and energy-intensive to remove the first electron from the most stable completely packed electronic state.

Note:
The ionisation energy of chemical compounds provides us with an indication of their reactivity. It may also be used to find out how strong chemical connections are. It can be expressed in electron volts or kJ/mol units. Ionization energy can be either adiabatic ionisation energy or vertical ionisation energy, depending on the ionisation of molecules, which typically results in changes in molecular geometry.