Which group has the highest ionization energy and why?

Table 8.2 in the textbook shows that the ionization energy increases when moving from left to right across a period. Thus, the alkali metals have the lowest ionization energy and the noble gases the highest. Within a group the ionization energy decreases as atomic number increases (Figure 8.2). read more

Ionization energy is the amount of energy required to remove one electron from an atom. So the groups further to the right of the periodic table would have greater ionization energies because they are more stable, so they don't want to lose electrons, and there is a greater number of protons attracting the negative charges (the electrons). read more

The element that has the highest first ionization energy is helium. The first ionization energy represents the amount of energy needed to make an atom into a positive ion, which is called a cation. Continue Reading. read more

Group 18, the noble gases, have the highest ionization energy because they have their complete set of eight valence electrons. read more