Here's why:
* Ionization energy is the minimum energy required to remove an electron from a gaseous atom or ion in its ground electronic state.
* First ionization energy refers to removing the first electron.
* Second ionization energy refers to removing the second electron after the first one has already been removed.
Factors affecting second ionization energy:
* Nuclear charge: A higher nuclear charge (more protons) attracts electrons more strongly, making it harder to remove another electron, increasing the ionization energy.
* Electron shielding: Electrons in inner shells shield outer electrons from the full nuclear charge. This shielding effect is weaker when removing the second electron, as there is one less electron shielding the nucleus.
* Electron configuration: Removing an electron from a filled or half-filled subshell requires more energy than removing one from a partially filled subshell.
Note: The second ionization energy is always higher than the first ionization energy. This is because removing an electron from a positively charged ion requires more energy than removing one from a neutral atom.
Example:
For example, the second ionization energy of sodium (Na) is 4562 kJ/mol. This means that 4562 kJ of energy are required to remove the second electron from a sodium ion (Na+), which has already lost its first electron.
To calculate the total energy required to remove two valence electrons, you would add the first and second ionization energies.
