Which of the three elements has the highest ionization energy-fluorine, oxygen and neon?

Dear student,

As three elements are given from different groups but same period.
The electronic configuration of oxygen is 1s22s2 2p4 
electronic configuration of fluorine is 1s2 2s2 2p5
electronic configuration of neon is 1s2 2s2 2p6
Ionisation energy is the amount of energy required to remove outermost electron from the atom.
As we know when we move from left to right in the periodic table the number of protons increases hence there is higher attraction on the electrons and large amount of energy is required to remove the electron.
When we compare oxygen and fluorine, as you see from electronic configuration that the number of protons are more in fluorine than oxygen, the nuclear attraction will be higher in fluorine than oxygen. Therefore, first ionisation energy of fluorine is higher than oxygen.
When we compare neon and fluorine , you can see that neon has fully filled p orbital hence, it is a stable atom . Large amount of energy is required in case of neon to remove an electron than fluorine
Order of ionisation energy as;  oxygen < fluorine < neon 


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oxygen is the answer
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