[Q.Solved] Rank These Elements According To First Ionization Energy

Students often get confused when they come across a question which asks them to arrange or rank elements according to the First Ionization Energy. Let us look at some examples and I will explain each of them along with it.

You may also want to learn about : Ionization Energy and Successive Ionization Energy. [First, Second, Third, Fourth Ionization Energy]

Rank Kr, Br, Se, As, Ge, Ga , Ca, K According To First Ionization Energy

The elements Kr, Br, Se, As, Ge, Ga , Ca, K are placed in Group 1, Group 2, Group 13, Group 14, Group 15, Group 16, Group 17 and Group 18 of the Modern Periodic Table. 

They might be placed in different groups, but they all do have a similarity. They are all placed in the 4th Period.

But there is a general trend that the elements in the periodic table follow. Ionization Energy increases on going towards the right side of the table. 

This makes it easy to solve this question. 

So the answer is,

K < Ca < Ga < Ge < As < Se < Br < Kr

Rank Ne, F, O, N, C, B, Be, Li According To First Ionization Energy

The elements Ne, F, O, N, C, B, Be, Li are placed in Group 18, Group 17, Group 16, Group 15, Group 14, Group 13, Group 2 and Group 1 respectively.

They are all members of the 2nd Period.

Just as they are the members of the same period. The aforementioned rule will be applied. 

So the correct arrangement of the above elements according to the first ionization energy will be:

Li < Be < B < C < N < O < F < Ne

Rank These Elements According to First Ionization Energy: P, Cl, Na, S, Mg, Al, Si, Ar.

The elements P, Cl, Na, S, Mg, Al, Si, Ar belong to the third period in the modern periodic table. 

Because, all the given elements belong to the same period. It follows the same rule. 

The Ionization Energy decreases as we move across the period.

Na < Mg < Al < Si < P < S < Cl < Ar

From the above examples we can see that the tendency of the metal ions to ionize is very high. It is mostly because of its electronic configuration. Also their size is larger if compared to the transition elements or the non metals. 

As the metals have a larger size and there is a prominent amount of screening effect the nucleus does not exert as much force to hold to the electrons close because of the distance between the nucleus and the orbital. Because the force of attraction is low, they readily lose electron.

The non metals on the other hand, have a tendency to gain electrons. They need electrons to attain a stable electronic configuration. They are smaller in size. Their nucleus exerts a lot of force of attraction and keeps the electrons close to the nucleus. This prevents them from ionizing easily.

Non metals show Penetration effect which in turn helps the nucleus pull electrons towards itself. The penetration effect follows the following order:

s > p > d > f


Thus we can say that the non metals have a higher ionization energy than that of metals. 
Along with this, remembering that Ionization Energy increase when we move across a period and decreases down the group will also help to solve the questions of this kind.

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