Ionization energy (or Ionisation energy) of group (alkali metals) 1 elements

periodic tableIonization energy is an important property for the elements. It helps to understand the affinity of an element for electrons as well as the tendency of the elements to form a ionic or covalent bonds. So what is the Ionization energy?

Ionization energy

The energy needed to remove the most loosely attached 1 mole electron of an isolated gaseous 1 mole atom to form one mole cation. That means the energy needs to remove 1 mole electrons from 1 mole metal. The 1 mole metal already in the gaseous state.

We can write a general equation to describe the removal of an electron from the metal.

M(g) + energy = M+(g) + e

here, M= the group 1 elements (alkali metals)

Ionization energy of atoms in the periodic table reveals two patterns:

 generally-

  1. increases as one moves from left to right within a given period.
  2. decreases as one moves down a given group.

What is 1st, 2nd, 3rd Ionization energy

Now, it can be 1st , 2nd , 3rd etc..

the energy needs to remove a mole of electron from the gaseous one mole atoms is first ionization energy. Same as the energy needs to remove a mole of electron from the gaseous one mole of the species with a charge of +1.

1st ionization energy: M → M+ + e
2nd ionization energy: M+ → M2+ + e
3rd ionization energy: M2+ → M3+ + e
nth ionization energy: M(n-1)+ → Mn+ + e

So nth ionization energy refers to the amount of energy required to remove an electron from the species with a charge of +(n-1).

1st Ionization energy Of group I

Period Name
(Symbol)
Atomic Number
(Z)
Simple Electronic Configuration Atomic Radius (pm) First Ionization Energy
(kJ/mol
)
 

 

 

decreasing

2 Lithium
(Li)
3 2,1 152 526
3 Sodium
(Na)
11 2,8,1 186 504
4 Potassium
(K)
19 2,8,8,1 231 425
5 Rubidium
(Rb)
37 2,8,18,8,1 244 410
6 Ceasium
(Cs)
55 2,8,18,18,8,1 262 380
7 Francium
(Fr)
87 2,8,18,32,18,8,1 370

From the above table we can see that the 1st ionization energy of the group 1 elements are low and gradually decreasing with the increasing atomic radius.

Reason of decreasing 1st Ionization energy Of group I with with radius

As the last electron of the group 1 elements is loosely attached to the nucleus, it’s easy to remove the electron from the atom. That is why the ionization energy of the group 1 elements are low. Besides when the atomic radius is increasing with the period, the distance between the last electron which is loosely attached to the nucleus ans nucleus increases. So the nucleus can’t attract the last electron strongly. As a result the ionization become easier and it needs less energy.

ionization energy

Reason of Low 1st Ionization Energy Of Group I

The reason of the low 1st ionization energy is hidden in the electronic configuration of the elements.

Period Name
(Symbol)
Atomic Number
(Z)
Simple Electronic Configuration First Ionization Energy
(kJ/mol
)
2 Lithium
(Li)
3 2,1 526
3 Sodium
(Na)
11 2,8,1 504
4 Potassium
(K)
19 2,8,8,1 425
5 Rubidium
(Rb)
37 2,8,18,8,1 410
6 Ceasium
(Cs)
55 2,8,18,18,8,1 380
7 Francium
(Fr)
87 2,8,18,32,18,8,1 370

From the above table we can see that the last shell of the atom has only one electron. The single electron is in the last shell and very weakly attached as well as the it is long away from the nucleus. So the ionization process needs low energy

2nd Ionization energy Of group I

Period Name
(Symbol)
Atomic Number
(Z)
Simple Electronic Configuration Atomic Radius (pm) Second Ionization Energy
(kJ/mol
)
 

 

 

decreasing

2 Lithium
(Li)
3 2,1 152 7296
3 Sodium
(Na)
11 2,8,1 186 4563
4 Potassium
(K)
19 2,8,8,1 231 3069
5 Rubidium
(Rb)
37 2,8,18,8,1 244 2650
6 Ceasium
(Cs)
55 2,8,18,18,8,1 262 2420
7 Francium
(Fr)
87 2,8,18,32,18,8,1 2170

From the above table we can learn that the 2nd ionization energy also decreasing with the increasing atomic radius. But the energy needed is for second ionization is very large.

Reason of high 2nd Ionization energy Of group I

Like low 1st ionization the reason of high 2nd ionization energy also depends on the electron configuration of the elements. As we know that the 2nd ionization energy refers to the amount of energy required to remove an electron from the species with a charge of +1. Therefore after 1st ionization the group 1 element got +1 charge.

name electronic configuration After 1st Ionization Electronic configuration of ions
Lithium (Li) [He],1 Li+ [He]
Sodium (Na) [Ne],1 Na+ [Ne]
Potassium(K) [Ar],1 K+ [Ar]
Rubidium(Rb) [Kr],1 Rb+ [Kr]
Caesium (Cs) [Xe],1 Cs+ [Xe]
Francium (Fr) [Rn],1 Fr+ [Rn]

From above we can understand that after the 1st ionization the group 1 elements looses one electron. As a result the electronic configuration of the group 1 elements having +1 charge is same as the inert gas. That means the electronic configuration is very stable and they does not want to loos another electron. As a result the 2 ionization process needs much more energy then the 1st ionization process.

Thanks for reading.

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