Question

Ionisation energy of He ion is 54.4 ev calculate
ionisation energy of Li ions?
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Answer 1

ionisation energy is the amount of energy required to remove an electron from an isolated gaseous atom.

from Bohr's theory,

ionisation energy, E = 13.6 × Z²/n² , where Z is atomic number and n is nth orbit from which an electron is ejected.

given, ionisation energy of He is 54.4 eV

for He , Z = 2 and n = 1

then, you will get, E = 13.6 × 2²/1² = 54.4eV

now for Lithium , Z = 3 And n = 1

so, ionisation energy ,E = 13.6 × Z²/n²

= 13.6 × (3)²/1²

= 13.6 × 9

= 122.4eV

hence, answer should be 122.4eV