Question

Which has lower ionisation enthalpy and why (Cl 17 or Ar 18)​

Answer 1

Answer:

Ionization energy is the energy required to remove the electron from outermost she'll in the neutral gaseous atom.

CI element have atomic no. =17

When we write the electronic configuration of it, 1s22s22p63s23p5

Which means there are 7 valence electrons. And it need one more electron to complete it's octet. For that matter the removal of one electron from the present valence shell requires more energy as the removal make the configuration more unstable. So it's first ionization energy is 1255kJ/mol.

Next is argon. Atomic no 18

Configuration is 1s22s22p63s23p6

We can see that it is stable electronic configuration with completely filled shells.

Here if we remove one electron, it's stability is lost. So it requires high energy for removing first electron. This is the reason why inert gases posses highest ionization energy along the period. For argon the first ionization energy is 1520kJ/mol.

The energy for this process is minimum as it is only one electron which makes the atom unstable. Therefore first ionization energy of K is 419kJ/mol

So the elements are arranged according to their first ionization energy as the first ionization energy defines whether an atom is stable or unstable due to removal of one electron from its valance shell .

So the order becomes

Ar > Cl

Answer 2

Answer:

Chlorine has low I.E when compared to Argon

Explanation:

Ionisation enthalpy increases across the period and decreases down the group

Noble gases have complete octet configuration and hence difficult to remove the outermost electrons due to stronger force of attraction or increased effective nuclear charge on valence electrons when compared to chlorine

Hence Ionisation enthalpy is highest for Argon than chlorine