<P> The term ionization potential is an older name for ionization energy, because the oldest method of measuring ionization energies was based on ionizing a sample and accelerating the electron removed using an electrostatic potential . However this term is now considered obsolete . Some factors affecting the ionization energy include: </P> <Ol> <Li> Nuclear charge: the greater the magnitude of nuclear charge the more tightly the electrons are held by the nucleus and hence more will be ionization energy . </Li> <Li> Number of electron shells: the greater the size of the atom less tightly the electrons are held by the nucleus and ionization energy will be less </Li> <Li> Effective nuclear charge (Z): the greater the magnitude of electron shielding and penetration the less tightly the electrons are held by the nucleus, the lower the Z of the electron, and hence less will be the ionization energy . </Li> <Li> Type of orbital ionized: the atom having a more stable electronic configuration has less tendency to lose electrons and consequently has high ionization energy . </Li> <Li> Occupancy of the orbital matters: if the orbital is half or completely filled then it is harder to remove electrons </Li> </Ol> <Li> Nuclear charge: the greater the magnitude of nuclear charge the more tightly the electrons are held by the nucleus and hence more will be ionization energy . </Li> <Li> Number of electron shells: the greater the size of the atom less tightly the electrons are held by the nucleus and ionization energy will be less </Li>

The quantum number of free gaseous atom is related to