Ionisation Energy & Electronic Configuration (Cambridge (CIE) AS Chemistry): Revision Note
Exam code: 9701
Ionisation Energies: Electronic Configuration
Using Successive Ionisation Energy Data
Each ionisation energy shows the energy needed to remove an additional electron from an atom in the gaseous state
As electrons are removed, the ion becomes more positively charged, and the remaining electrons are held more tightly. This causes ionisation energies to increase
A large jump in successive ionisation energies indicates that the next electron is being removed from a new, inner shell
How to deduce electronic configuration
Look for the largest increase between two successive ionisation energies
The number of electrons removed before this jump = number of outer-shell (valence) electrons
This corresponds to the element’s group number in the Periodic Table (for s- and p-block elements)
Worked Example
Deduce the electronic configuration of element Z, a Period 3 element, using successive ionisation energy data.
IE | 5th | 6th | 7th | 8th |
|---|---|---|---|---|
IE (kJ mol-1) | 6542 | 9362 | 11,018 | 33,606 |
Answer
You are told that the element is in Period 3
Period 3 elements have electrons up to the 3rd shell:
3s and 3p subshells are included
There is a large jump between the 7th and 8th IE, so element Z must be in Group 17
So element Z is in Period 3 and Group 17:
This corresponds to chlorine, Cl
The electronic configuration of Cl is:
1s22s22p6 3s23p5
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