Ionisation Energy
Chemical trends
- All elements in Group 2 (also called alkali earth metals) have two electrons in their outermost principal quantum shell
- All Group 2 metals can form ionic compounds in which they donate these two outermost electrons (so they act as reducing agents) to become an ion with +2 charge (so they themselves become oxidised)
- Going down the group, the metals become more reactive
- This can be explained by looking at the Group 2 ionisation energies:
The graph shows that both the first and second ionization energies decrease going down the group
- The first ionisation energy is the energy needed to remove the first outer electron of an atom
- The second ionisation energy is the energy needed to remove the second outer electron of an atom
- The graph above shows that going down the group, it becomes easier to remove the outer two electrons of the metals
- Though the nuclear charge increases going down the group (because there are more protons), factors such as an increased shielding effect and a larger distance between the outermost electrons and nucleus outweigh the attraction of the higher nuclear charge