Ionization and electron affinity

[Joanna Huang]

Can someone explain exactly what ionization energy and electron affinity is? I'm still a bit confused on what is it and the trends on the periodic table.

[Savana Maxfield 3F]

Hi! Ionization energy is the amount of energy required to remove the most loosely bounded electron of an atom or molecule. Electron affinity is the amount of energy released when an electron attaches to a neutral atom/compound.

[Natalie 3k]

Ionization energy is the amount of energy that is required to remove an electron, and more specifically the least bound electron to the atom. Elements that only have one valence electron have lower ionization energies because removing the one electron would make it have a full outer shell. As you move down a group elements gain more and more orbitals so the farthest electrons are farther from the positive charge of the nucleus. Electron affinity is somewhat the opposite, it is how much energy is released or required to give an atom an extra electron. Elements like fluorine that have 7 electrons have low electron affinity because it is close to a full outer shell so it is easier to gain one than an element like sodium which would want to get rid of its electron. Hopefully someone can explain a little more detailed and correct me if I'm wrong.

[Jillian Labador 3E]

Ionization energy is the energy required to remove an electron from an atom in the GAS phase. It is a similar concept to the photoelectric effect; however, the different phases of the element distinguishes them from each other. When considering trends, ionization energy increases as you move across a period because there is an increase in the nuclear charge from the addition of protons which makes it more difficult to remove an electron. It decreases as you move down a group because the addition of shells creates a larger atomic radius, making it easier to remove an electron.

Electron affinity is the energy that is released or required for an electron to be added to an atom in the gas phase. Halogens in group 17 have the highest electron affinity because they need one more electron to transition to a more stable state. Noble gases in group 18, however, have a negative electron affinity because they are already in a stable state and do not want to gain an electron, so energy is required for an electron to be added.

[Yun Su Choi 3G]

Hi Joanna! IE is the energy needed to remove one electron. IE decreases down a group as the number of shells increase and the shielding effect is strengthened as the electrons of the inner shells balance out the positive charge from the nucleus, making it easier for the electron in the outer shell to be removed. IE increases across a period as the number of shells stay the same (electron shielding from the inner e- stays the same) but the positive nuclear charge increases, making it harder for the electron to be removed.
Electron affinity, on the other hand, is the energy released when an e- is added to the neutral atom to turn into an anion. A release of energy means that the atom is transitioning to a more stable state (rule of thumb: more stable=lower energy, less reactive). So the element most likely to gain an electron will release the most energy (eg: group 17 atoms). For example, Cl(group 17) will have higher electron affinity(release more energy) than Al. In fact, Cl has the highest electron affinity in the periodic table. On the contrary, He(already stable with 2 e-) will absorb more energy than Al because absorption corresponds to transition of a less stable state.

[Ayesha Aslam-Mir 3C]

Hi, I just wanted to pose a further quesiton; electron affinity involves energy released when an electron is added to an atom; even though it only applies to atoms in their gaseous form, does this essentially hold true with the trend of ionization energy and electronegativity always? Additionally, if an electron being added to an atom releases energy, does this imply any energy based limitations in bonding?

[Brandon McClelland3L]

Ionization energy is the amount of energy required to strip the atom of an electron. The electron affinity of an atom is how easily it can accept an additional electron.