Ionization Energy vs Electron Affinity
Atoms are the small building blocks of all existing substances. They are so tiny that we can’t even observe with our naked eye. Atom is made up of a nucleus, which has protons and neutrons. Other than neutrons and positrons there are other small sub atomic particles in the nucleus. In addition, there are electrons circling around the nucleus in orbital. Because of the presence of protons, atomic nuclei are positively charged. The electrons in the outer sphere are negatively charged. Hence, the attractive forces between the positive and negative charges of the atom maintain the structure.
Ionization energy is the energy that should be given to a neutral atom to remove an electron from it. The removal of electron means that to remove it an infinite distance from the species so that there are no attraction forces between the electron and the nucleus. Ionization energies are named as first ionization energy, second ionization energy, and so on depending on the number of electrons removing out. This will give rise to cations with +1, +2, +3 charges and so on. In small atoms, the atomic radius is small. Therefore, the electrostatic attraction forces between the electron and the neutron is much higher compared to an atom with larger atomic radius. This increases the ionization energy of a small atom. When electron is located closer to the nucleus, ionization energy increases. Thus, the (n+1) ionization energy is always higher than the nth ionization energy. In addition, when comparing two 1st ionization energies of different atoms, they also vary. For example, first ionization energy of sodium (496 kJ/mol) is much lower than the first ionization energy of chlorine (1256 kJ/mol). By removing one electron, sodium can gain the noble gas configuration; hence, it readily removes the electron. And also the atomic distance is less in sodium than in chlorine, which lowers the ionization energy. So, ionization energy increases from left to right in a row and bottom to top in a column of the periodic table (this is the inverse of atomic size increase in the periodic table). When removing electrons, there are some instances where the atoms gain stable electron configurations. At this point, ionization energies tend to jump into a higher value.
Electron affinity is the amount of energy released when adding an electron to a neutral atom in producing a negative ion. Only some atoms in the periodic table are undergoing this change. Noble gases and some alkaline earth metals do not favor adding electrons, so they don’t have electron affinity energies defined for them. But p block elements like to take in electrons in order to gain the stable electron configuration. There are some patterns in the periodic table regarding the electron affinities. With the increasing atomic radius, electron affinity is reduced. In the periodic table across the row (left to right), atomic radius decreases, therefore, the electron affinity is increased. For example, chlorine has higher electron negativity than sulfur or phosphorus.
What is the difference between Ionization Energy and Electron Affinity?
• Ionization energy is the amount of energy needed to remove an electron from a neutral atom. Electron affinity is the amount of energy released when electron is added to an atom.
• Ionization energy is related with making cations from neutral atoms and electron affinity is related with making anions.