Today we are going to take a look at the 3 Factors Affecting Ionisation Energy in atomic structure. We have looked at the formal definition of ionisation energy previously and it’s really important that you are comfortable with that first.

3 Factors Affecting Ionisation Energy

1. Size of the positive nuclear charge

As the nuclear charge increases, its attraction for the outermost electron increases and more energy is required to remove an electron.

This means that the ionisation energy increases.

2. Size of atom (distance of outermost electron from the nucleus)

As atomic size increases, the attraction of the positive nucleus for the negative electron decreases and less energy is required to remove an electron.

This means that the ionisation energy decreases.

3. Screening  (shielding) effect of inner shell electrons

The outermost electron is screened (shielded) from the attraction of the nucleus by the repelling effect of the inner electrons.

As shielding increases, the attraction of the positive nucleus for the negative electron decreases and less energy is required to remove an electron.

This means that the ionisation energy decreases.

Test Yourself NOW!

Let us take a look at a modified multi-choice question taken from GCE A-Level Higher 2 (H2) Chemistry Examination which is set by Ministry of Education, (MOE) Singapore in collaboration with University of Cambridge Local Examinations syndicate (UCLES).

Question:

Why is the first ionisation energy of neon higher that that of fluorine?

A) The atomic radius of fluorine is less than that of neon

B) The nuclear charge in neon is greater than that in fluorine

C) Neon has a complete octet, but fluorine does not

D) Fluorine is more electronegative than neon

Answer:

Option (B)

Suggested Solution:

Neon and fluorine are in the same period of the Periodic Table.

Ionisation energy increases across a period due to increasing nuclear charge and decreasing atomic radius.

Since the electrons all go into the same shell, the shielding of the ionisation electrons is about the same.

The outer electrons are, therefore, increasingly more strongly attracted by the positive nucleus, and so, more energy is required to remove an electron in neon than in fluorine.

Common Mistakes:

Note that the atomic radius of fluorine is less than that of neon. Thus, answer is NOT option (A) in which many JC A-Level H2 Chemistry students would choose.

GCE A-Level H2 Chemistry Ten Year Series (TYS) Books

The above suggested solution is also shared in my GCE A-Level H2 Chemistry Ten Years Series (TYS) Books. It contains questions from Year 2008-2017 and all suggested answers are written by me personally.

Both Topical and Yearly Editions are available in all Singapore Popular Bookstores as well as JC school bookshops. I am honoured to be invited by Singapore Asia Publishers Pte Ltd (SAP) to write these TYS books. The books are recommended by H2 Chemistry JC lecturers in Dunman High, River Valley High, Temasek Junior College (TJC), Meridian Junior College (MJC), Pioneer Junior College (PJC) and National Junior College (NJC). I was also told by students in my JC A-Level H2 Chemistry Tuition Classes that the books are also recommended by some of their H2 Chemistry Tutors in Raffles Junior College (RJC), Hwa Chong Institution (HCI), Anglo Chinese Junior College (ACJC) and Nanyang Junior College (NYJC).

You can grab a copy and start to work on the questions to improve your H2 Chemistry grades now!

I hope you find the content easy for your understanding and if you have any questions, leave me a comment below. Feel free to share this blog post with your friends. This topic is usually discussed in JC1 (Junior College Year 1) in Singapore.

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PS: Under related articles below, there are several blog post discussions and questions related to Atomic Structure and Ionisation Energies. You can also do a keyword search using the search box at the top right hand corner.