[Explained] Why Do Metals Have Low Ionization Energy?

 In this post we will try to understand why do metals have low ionization energy.

The most accurate answer for the question why do metals have low ionization energy, is:

Metals have a large atomic radii, they have low nuclear charge, they exhibit screening effect, they have a higher penetration effect and they have an unstable electronic configuration. This is why metals have a low ionization energy.

On the other hand non-metals have high ionization energy.

Now let us try and understand what each of those mean and how they affect the ionization energy of metals.

 Metals are those elements which are shiny, hard (sometimes soft such as the alkali metals) and shiny in appearance.

They have an electropositive nature which means that they have a tendency to lose electrons and achieve the electron configuration of the nearest noble gas. They have very few electrons in their valence shell. They are reactive in nature.

They are generally very dense elements which are also malleable and ductile.

They conduct heat and electricity very well, and thus find many industrial and household usage. And the very high melting and boiling points that they possess helps in this.

Now let us understand what ionization energy is.

Ionization energy is the energy required to remove the most loosely bound electron from an isolated gaseous atom to form a gaseous ion.

It is expressed in the unit of kJ mol^-1

Metals have low ionization energy due to the following factors which govern ionization energy:

• Size of the atom
• Nuclear Charge
• Screening Effect also known as Shielding effect
• Penetration Effect
• Electronic Configuration

We will discuss all of these factors with respect to metals and the reason behind them having such low ionization energy.

Size of the Atom

As you might know that metals have a large atomic size. The ionic radii of metal ions are smaller than atomic radii of corresponding atoms.

This is because the removal of electron shell decreases the size.

An increase in atomic size results in a decrease in ionization energy.

The atomic and ionic radii of metals increase on moving down the group.

Nuclear Charge

The effective nuclear charge experienced by the remaining electrons is also increased.

As the effective nuclear charge increases the ionization energy also increases.

The metals have a low effective nuclear charge and non metals have a high effective nuclear charge.

Learn: Trends of Ionization Energy in the Periodic Table

The combined effect of the decrease in the number of electron shells and an increase in the effective nuclear charge is responsible for the smaller size of metal cations as compared to those of the corresponding metal ions.

In going from left to right across a period, i.e. going from metal elements to non metal elements in the periodic table, the number of shells remain the same but nuclear charge increases with each succeeding element. Thus, the electrons in the valence shell experience  a greater pull towards the nucleus.

Screening effect

The electrons present between the nucleus and the valence electron shield the valence electron from the nucleus.

This in turn reduces the pull exerted by the nucleus on valence electrons.

Thus, ionization energy decreases with an increase in the number of inner electrons.

Metals have many inner electrons. 

Penetration Effect of Electrons

In a multielectron atom, the electron clouds of various electrons do not maintain distinct boundaries. Instead, the electron cloud of one electron penetrates into the electron cloud of some other inner electron. This effect is known as the penetration effect.

Due to this effect, electrons shift towards the nucleus and experience a greater pull by it.

For the same value of n (principle quantum number) the ionization energy of s electron is greater than that of a p electron which in turn is greater than that of a d electron, which is in turn greater than that of a f electron. 

Also Read: Why does Ionization Energy decrease down the group?

Electronic Configuration

Half-filled and completely filled shells are found to have extra stability.

And these atoms possess less tendency to lose electrons.

Most metals have an unstable electronic configuration. So they tend to lose electrons easily. That is why they have low ionization energy.

Conclusion

Metals have a large atomic radii, they have low nuclear charge, they exhibit screening effect, they have a higher penetration effect and they have an unstable electronic configuration. This is why metals have a low ionization energy.