Question

The table below lists the first five ionization energies of a second period elements
Identify the element.

	Ionisation Energy (KJ/mol)
First	801
Second	2430
Third	3660
Fourth	25000
Fifth	32820

A) Lithium (Li)
B) Beryllium (Be)
C) Boron (B)
D) Carbon (C)

Answer 1

Hint: The ionization energy can be described as the energy required to remove the electron from its valence shell. So, from this definition we can find which period shows this trend of ionization energy.

Complete answer:
We know that from the definition of ionization energy it is the energy required to remove its electron from the valence shell. Now first ionization energy means the energy required to remove the first electron from its neutral atom. And when we remove the next electron from its valence shell it is known as second ionization energy.
So, when we remove the second electron, it will already be positive and hence the second ionization energy will be greater when compared with first ionization energy. This trend also goes on with removing electrons.
Now coming to our question, we can see that the trend we discussed earlier is being followed here. But when observing the values we can see that there is a large increase in ionization energy from third to fourth. The third ionization energy value is 3,660 and fourth ionization energy is 25,000. That is a very steep increase.
What will be the reason? So, we know that it is very difficult to remove an electron from its valence shell if it is fully filled or half-filled since they are very stable. This suggests that when we remove the third electron from its valence shell it is very stable implies it must be full filled. From this we understand that it has 3 valence electrons.
Coming to our option only Boron (B) has 3 electrons in its valence shell.

Therefore option (c) is correct.

Note: It must be noted that there are some exceptions in trends for Ionization energy. When we move from left to right of the periodic table the general trend is increasing ionization energy. Still there are some discrepancies as the first ionization of Boron is less than that of beryllium and the first ionization of oxygen is less than that of nitrogen. The reason for this is the same we explained before, due to the completely filled or half-filled valence shell.