Arrange these elements according to first ionization energy.

Rank these elements according to first ionization energy (highest to lowest) : Ne, F, O, N, C, B, Be, Li.

HINT: There is a general trend for ionization energy within a period of the periodic table. However, elements with a filled s or half-filled p subshell have a higher ionization energy than expected by the general trend.


General guidance

Concepts and reason

The progressive filling of the electrons in the atomic orbitals based on their increasing energies is given by the electronic configuration of the atom.

The elements whose atoms have similar valence electronic configuration and hence exhibit similar chemical properties are placed in a vertical arrangement called a group.

The elements in whose atoms, the final valence electron enters the same orbital are placed in horizontal arrangements called periods.

The combination of the periods and groups form the Long form periodic table or Moseley’s Periodic table.


First ionization energy: The energy that is to be supplied to extract the outermost valence electron from an atom is termed as the first ionization energy.

The general periodic trend of variation in this energy is as follows:

Ionization energy, tend to increases upon moving from left to right of a period.

Ionization energy, decreases upon moving from top to bottom of a group.


Step 1 of 2

The locations are as follows:

Neon (Ne): Group 18; Period 2

Fluorine (F): Group 17; Period 2

Oxygen (O): Group 16; Period 2

Nitrogen (N): Group 15; Period 2

Carbon (C): Group 14; Period 2

Boron (B): Group 13; Period 2

Beryllium (Be): Group 2; Period 2

Lithium (Li): Group 1; Period 2

All elements belong in the same period. Hence, only the group number decides the order of the ionization energies. Higher the group number, higher is the expected ionization energy. This is a direct consequence of the increasing nuclear charge.

Step 2 of 2

The ionization energies (inkJ mol-) are as follows:

Neon (Ne): 2080.7

Fluorine (F): 1681.0

Oxygen (O): 1313.9

Nitrogen (N): 1402.3

Carbon (C): 1086.5

Boron (B): 800.6

Beryllium (Be): 899.6

Lithium (Li): 520.2

Thus, the ionization energy follows the trend: Ne>>N>O>>Be>B>Li.

The ionization energy follows the trend: Ne>F>N>0>C> Be>B> Li.

The electronic configuration of Nitrogen is given as:. The exactly half filled state of the p orbital imparts an additional stability to the atom. The electronic configuration of Beryllium is given as:. The completely filled state of the valence’s orbital imparts an additional stability to the atom.This causes the anomalous position of the N and Be atoms in the hierarchy. is noble gas, it has the completed atomic orbital, it is difficult to remove the electron from the completely filled atomic orbitals. So it occupies the first position in the ranking. While the ionization energy trend of other atoms increases upon moving from left to the right of the period. The final ionization energy order will be Ne>>N>O>>Be>B>Li.


The ionization energy follows the trend: Ne>F>N>0>C> Be>B> Li.

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