Question

The correct order of ionization energies is:
A.${\text{Cu}} > {\text{Ag}} > {\text{Au}}$
B.${\text{Cu}} > {\text{Au}} > {\text{Ag}}$
C.${\text{Au}} > {\text{Cu}} > {\text{Ag}}$
D.${\text{Ag}} > {\text{Au}} > {\text{Cu}}$

Answer 1

These three elements belong to the same group of periodic tables that is group number 11. As we move down the group ionization energy decreases, but in the above case one exception arises due to f electrons and its ionization energy becomes high.

Complete step by step answer:
${\text{Cu}}$ is a chemical symbol for copper, ${\text{Ag}}$ is a chemical symbol for silver and ${\text{Au}}$ is a chemical symbol for gold.
Ionization energy is the minimum amount of energy that is required to remove an electron from the valence shell of an isolated gaseous atom. Ionization energy is always calculated when the atom is in gaseous state and not in solid or liquid state. It is also known as ionization potential. Electrons are bonded to the nucleus through force of attraction; hence we have to provide an external energy to break the intermolecular forces of attraction that is why ionization is an endothermic process.
There is an effect known as shielding effect. In which the electrons present in the inner orbital’s of an element causes shielding or reduces interaction in between the nucleus and the electron due to which the force of attraction decreases.
d and f orbital have very poor fielding because of their shapes and hence whenever d and f orbital are filled the force of attraction between nucleus and electron is high compared to when s and p orbitals are present.
The order of shielding is as follow
s> p > d > f
Usually down the group ionization energy decreases. Both copper and silver have only d orbital filled whereas in gold f electrons are also filled due to which the shielding effect is very less in gold atoms. So, the force of attraction between nucleus and Valence electrons is high and so the ionization energy.

The correct order is ${\text{Au}} > {\text{Cu}} > {\text{Ag}}$ that is option C.

Note:
Ionization energy depends upon various factors such as, if the distance between nucleus and electron is more than the force of attraction will be less and has the electron in easily removed so ionization energy will be less. If the distance is less between electron and nucleus then ionization energy will be high. Similarly if charge on the nucleus is high then the force of attraction will be more in hence ionization energy will be more.