Question

The energy of an electron in the ground state of a $H$-atom is $-2.15\times {10}^{-18}J$. The Ionisation energy of the atomic hydrogen in terms of ${10}^{5}Jmo{l}^{-1}$ is:

• A. $14$
• B. $13.5$
• C. $12$
• D. $13$

Answer 1

The correct option is D $13$

Ionisation energy is the energy required to remove the outermost electron from an isolated gaseous atom.

Hence, the required energy will be equal to the amount of energy which is holding the electron to the nucleus.

$IE$ required to remove an electron is $2.15\times {10}^{-18}J$.
So, for $1mol$, IE required will be $2.15\times {10}^{-18}\times N_A$
=$2.15\times {10}^{-18}\times 6.023\times {10}^{23}$
=$12.94\times {10}^{5}Jmo{l}^{-1}$
Rounding of to the nearest integer,
=$13\times {10}^{5}Jmo{l}^{-1}$.