How does shielding effect affect ionization energy?

The shielding effect, also known as electron shielding or screening effect, refers to the reduction in the effective nuclear charge experienced by an electron in an atom due to the presence of other electrons in inner energy levels or shells. This effect has a significant impact on the ionization energy of an atom.

Ionization energy is the energy required to remove an electron from an atom or ion in its gaseous state. The higher the ionization energy, the more difficult it is to remove an electron. The shielding effect affects ionization energy in the following ways:

Increased Shielding Leads to Lower Ionization Energy:
When electrons occupy inner energy levels or shells (closer to the nucleus), they act as a shield or screen that reduces the net positive charge felt by electrons in outer energy levels. The more inner shells there are between the outermost electron and the nucleus, the greater the shielding effect. As a result, the outermost electrons are held less tightly by the nucleus and are easier to remove, leading to lower ionization energy.

Decreased Shielding Leads to Higher Ionization Energy:
Conversely, if there are fewer inner electrons or less shielding between the outermost electron and the nucleus, the effective nuclear charge experienced by the outermost electron is higher. This increased attraction between the electron and the nucleus requires more energy to remove the electron, resulting in a higher ionization energy.

In summary, the shielding effect reduces the effective nuclear charge experienced by outermost electrons, making it easier to remove them and leading to lower ionization energy. The number of inner electrons and their distribution in an atom play a crucial role in determining the shielding effect and, consequently, the ionization energy of that atom.