Ionization energy is defined as

Ionization energy is defined as

• A. The energy required to remove a neutron from an atom
• B. The energy required to remove an electron from an atom
• C. The energy released when an electron attaches to an ion
• D. The energy required to add an electron to a neutral atom

Answer: (B)

Ionization energy is the energy required to remove an electron from a neutral atom in the gaseous state. It’s an endothermic process—energy must be put in to overcome the attraction of the positively charged nucleus on the electrons. This quantity is commonly discussed for the first electron removed (the first ionization energy) and helps explain trends across the periodic table. Removing a neutron would be a nuclear process, not an electronic one, so that isn’t ionization energy. The energy released when an electron attaches to an ion relates to electron affinity, not ionization energy. And the energy required to add an electron to a neutral atom is describing a process opposite to ionization energy and isn’t the standard definition either. So the correct idea is the energy needed to remove an electron from an atom.

Ionization energy is the energy required to remove an electron from a neutral atom in the gaseous state. It’s an endothermic process—energy must be put in to overcome the attraction of the positively charged nucleus on the electrons. This quantity is commonly discussed for the first electron removed (the first ionization energy) and helps explain trends across the periodic table.

Removing a neutron would be a nuclear process, not an electronic one, so that isn’t ionization energy. The energy released when an electron attaches to an ion relates to electron affinity, not ionization energy. And the energy required to add an electron to a neutral atom is describing a process opposite to ionization energy and isn’t the standard definition either. So the correct idea is the energy needed to remove an electron from an atom.