Topics of Discussion: Atomic Structure – Ionisation Energy
Today, we are going to discuss on a very important concepts in Advanced Chemistry (such as the Cambridge Singapore JC A-Level H2 Chemistry and IB HL Chemistry) known as Ionisation Energy. I am currently teaching students in our JC1 A-Level H2 Chemistry Tuition classes the said concept.
Let’s hit the road and get started by defining the term (NOTE that you will be asked to define it in your written examination). We normally will start by asking you to define the first ionisation energy.
First ionisation energy of an element is defined as the amount of energy required to remove one mole of electron from each atom in a mole of gaseous atoms producing one mole of gaseous cations.
(Do note the words in italics which is what your examiner will be looking out for.)
An equation can be used to represent the first ionisation energy:
X(g) -> X+(g) + e– ΔH1 = 1st ionisation energy = +ve
Ionisation energies normally have positive values since energy is taken in to remove an electron i.e. endothermic.
The successive ionisation energies of an element increase with the removal of each electron. Do you know why?
This is because the remaining electrons are attracted more strongly by the constant positive nuclear charge in the nucleus of the atom.
It is also important to note that the number of ionisation energies that an element can have is always equal to its atomic number.
For example, potassium, K (with atomic number = 15) could have ionisation energies up to 15th ionisation energy.
You can view the values of the first four ionisation energies of common elements in the Data Booklet HERE.
I am sure you have learned something useful today.
In the next blog post, i will share with some exam-based questions that are related to Ionisation Energy.
Meanwhile, feel free to share it with your friends who need help in Advanced Chemistry such as GCE A-Level H2 Chemistry in their Junior Colleges (JC).