Ionisation energy is the amount of energy required to remove an electron from a specific gaseous atom or ion. It applies to all the elements on the periodic table and not just the atoms that are gases at room temperature.
Trends and Periods
Looking at the periodic trend, as the students go from lithium over to neon, across the periodic table, the students can notice that there’s an increase in the ionisation energy. Lithium is positive 520 kilojoules per mole, and Beryllium’s goes up to 900 kilojoules per mole, and then again, in general, there’s an increase in ionisation energies going over to neon. That is because there’s also a relative increase in the effective nuclear charge. An ion is just an atom or a molecule with a charge, and it’ll have a charge if the protons are not equal to electrons. Neutrons are also composed of atoms but are neutral. The charge is given from protons or electrons, which is a net charge for an atom or molecule. A molecule’s just a cluster of atoms bonded together. The negative ions are more significant in the number of electrons than protons. So, for example, Hydrogen in its neutral state has one proton and one electron. Still, even if one of the electrons is taken away, then Hydrogen would have a positive charge, and essentially, it would just be, in its most common isotope, it would just be a proton by itself. And so, when it’s a positive ion where the number of protons is more than electrons, it is called Cations. Cation is just another word for positive ions. Likewise, we can have negative ions. For example, Fluorine. When fluorine gains an electron, it will have a negative charge. A negative ion is named an Anion.
With the help of Ionisation, one can ionise different elements in the periodic table and turn them into cations. However, turning the element into gas is necessary before moving onto the electron.
Metals have low ionisation energy, whereas nonmetals have high ionisation energy. Ionisation energy will increase from left to right, and it will rise from the bottom to the top on the periodic table. Therefore, the lowest ionisation energy will be Francium, and the highest ionisation energy will be Helium.