What is ionization energy and how does it relate to the periodic table?

Ionization energy is the energy required to remove an electron from an atom in its gaseous state.

Ionization energy is an important property of elements that can be used to predict their chemical behaviour. The trend in ionization energy across the periodic table is that it increases from left to right and decreases from top to bottom. This is due to the increasing nuclear charge and decreasing atomic radius as you move across a period, which makes it more difficult to remove an electron. Conversely, as you move down a group, the atomic radius increases and the outermost electrons are further away from the nucleus, making it easier to remove an electron.

The ionization energy of an element can also be used to determine its reactivity. Elements with low ionization energies tend to be more reactive because they are more likely to lose an electron and form positive ions. For example, the alkali metals have low ionization energies and are highly reactive, while the noble gases have high ionization energies and are relatively unreactive.

In summary, ionization energy is a measure of the energy required to remove an electron from an atom. The trend in ionization energy across the periodic table can be used to predict the chemical behaviour of elements and their reactivity.