Describe the periodicity of the first ionization enthalpy for elements with atomic numbers $1$ to $60$.

(N/A) Generally,ionization enthalpy refers to the first ionization enthalpy.
The first ionization enthalpies of elements with atomic numbers up to $60$ are plotted in the graph.
The periodicity of the graph is quite striking.
Maxima are observed at the noble gases,which have closed electron shells and very stable electron configurations.
Conversely,minima occur at the alkali metals,and their low ionization enthalpies can be correlated with their high reactivity.
Within a period,as we move from left to right,the ionization enthalpy generally increases.
Within a group,as we move from top to bottom,the ionization enthalpy generally decreases.