Question

What is the unit of ionization energy?
1. Joule
2. N/m²
3. KJ mol^-1
4. KJ m^-1

Answer 1

Correct Answer - Option 3 : KJ mol^-1

The correct answer is KJ mol-1.

• Ionization energy is the energy required to remove an electron from one mole of gaseous atoms.
  • Units = Energy/Mol
  • ​          = KJ/mol
  •             =KJ mol−1
• Hence, the correct option is 3.

• Ionization energy is the quantity of energy that an isolated, gaseous atom in the ground electronic state must absorb to discharge an electron, resulting in a cation.
  • H(g)→H+(g)+e⁻
• This energy is usually expressed in kJ/mol, or the amount of energy it takes for all the atoms in a mole to lose one electron each.
• The most notable factors affecting the ionization energy include:
  • Electron configuration: this accounts for most element's IE, as all of their chemical and physical characteristics can be ascertained just by determining their respective electron configuration.
  • Nuclear charge: if the nuclear charge (atomic number) is greater, the electrons are held more tightly by the nucleus and hence the ionization energy will be greater.
  • A number of electron shells: if the size of the atom is greater due to the presence of more shells, the electrons are held less tightly by the nucleus and the ionization energy will be lesser.
  • Effective nuclear charge (Zeff): if the magnitude of electron shielding and penetration is greater, the electrons are held less tightly by the nucleus, the Zeff of the electron, and the ionization energy is lesser.
  • Type of orbital ionized: an atom having a more stable electronic configuration has less tendency to lose electrons and consequently has higher ionization energy.
  • Electron occupancy: if the highest occupied orbital is doubly occupied, then it is easier to remove an electron.