Electron Affinity and Ionization Energy

[Ava Harvey 2B]

Hi! I was just wondering if someone could please explain to me the relationship between electron affinity and ionization energy. I know that their trend is the same or very similar throughout the periodic table, but I'm confused on what that relationship actually is and what it means. Thanks!

[Caroline C 1G]

Ionization energy is the energy needed to remove an electron from an atom in the gas phase. Electron affinity is the amount of energy that is released or acquired when an electron is added to an atom in the gas phase. The trends of electron affinity aren't as obvious as those of ionization energy on the periodic table, but the elements on the top right usually have a high electron affinity. I hope this answers your question!

[Isita Tripathi 2E]

Trends in ionization energy:
1. increases down a period (as the atomic number increases, the effective nuclear charge increases on each electron, making them more difficult to remove)
2. decreases down a group (as n increases, the valence electrons get farther away from the nucleus, making the electrostatic attraction lower)

Ionization energy measures the energy involved in forming cations, and electron affinity measures the energy involved in forming anions. Essentially, electron affinity measures the ability to attract electrons, while ionization energy measures the ability to hold on to electrons. Both of these things increase as the effective nuclear charge increases, and both decrease as the effective nuclear charge decreases. This is why they follow similar trends.

[Leah Thomas 2E]

Also you can think of it that if an atom can attract an electron easily, then the ionization energy will be big because it want to hold on to that electron for as long as it can.

[Jessica Beroukhim 3K]

If it helps, you can think of them as conceptually opposites. "Ionization energy is the energy needed to remove an electron from an atom in the gas phase. Electron affinity is the amount of energy that is released or acquired when an electron is added to an atom in the gas phase" sounds like they're opposite already, but if you remember it like this, note that electron affinity is calculated as the energy of the neutral atom minus the energy of the atom with an extra electron, so it's not necessarily "the energy needed". It depends on if it is positive or negative