Ionization energy , units, types and ionization energy trend

 IONIZATION ENERGY/ IONIZATION POTENTIAL

         Definition of ionization energy 

        The ionization energy is the least amount of energy released or absorbed when we remove an electron from the outermost shell of an individual gaseous atom. It is represented by ‘I’. We can directly measure the ionization energy.

Units

          The units for ionization energy are:

• Ø Kilocalories per mole
• Ø Electron volts per atom
• Ø Kj/ mole

Types

          Ionization energy is divided into three types

• _Ø   First ionization energy I₁
• _Ø   Second ionization energy I₂
• _Ø   Third ionization energy  I₃
• 
  

First ionization energy I₁

          The energy required to remove the first electron from the outermost shell of the individual gaseous atom is known as First ionization energy I₁

first ionization energy

Second ionization energy I₂

                The energy required to remove the second electron from the outermost shell of a singly positive gaseous atom is known as second ionization energy I₂

2nd ionization energy

Third ionization energy I₃

          The energy required to remove 3rd electron from the outermost shell of doubly positive gaseous atom is known as 3rd ionization energy I₃.

3rd ionization energy

                                                             I₁ < I₂  < I₃

          The first ionization energy is always less than 2^nd and 3^rd ionization energy and second ionization energy is less the 3^rd ionization energy.

Factors on which ionization energy depends

          Ionization energy depends upon different factors:

Ø Atomic radius

Ø Nuclear charge

Ø Shielding effect

Ø Penetration is the ability of outer electrons in the charge clouds of already present electrons of atom

Ionization energy trends

          Ionization energy has a different trend in periods and groups.

Trend in groups

          The ionization energy of elements decreases in groups from top to bottom with the addition of each new shell in each new period.

Reason

          Ionization energy decreases in a group because in each new period new shell is added to an element, so it becomes very easy to remove electrons from an outermost shell. So for the removal of electron require very less energy.

Trend in periods

          Ionization increase in a period from left to right with the increase of nuclear charge in each new group.

Reason

          Ionization energy increases from left to right in a period because in each new element nuclear charge increases. Due to the increase of nuclear charge, the nucleus tightly bound the outermost shell electrons, as a result, the atomic radius of elements decreases and it becomes very difficult to remove electrons from an outermost shell. So for the electron requires very high energy.