Answer :
Answer:
Electron affinity generally decreases down a group of elements because each atom is larger than the atom above it (this is the atomic radius trend, discussed below). This means that an added electron is further away from the atom's nucleus compared with its position in the smaller atom.
Taking into account hte definition of electron affinity and atomic radius, electron affinity increases from left to right, and from bottom to top in the periodic table, in the opposite direction to the atomic radius.
- Electron affinity
Electron affinity is the energy released when an electron is added to a neutral atom in the gaseous state. When an electron is added to a neutral atom, an anion with a charge equal to -1 is formed.
That is, electron affinity is defined as the energy involved when a neutral gaseous atom in its ground state (of minimum energy) captures an electron.
- Atomic radius
On the other hand, the atomic radius is defined as the most probable distance of the outermost electron from the nucleus. However, because the electron cloud that surrounds the nucleus has no definite limits, the size of an atom is determined by its interaction with the atoms that surround it. So the atomic radius is defined as half the distance between two nuclei of two adjacent atoms.
- Shielding and effective nuclear charge
Before relating the ionization energy to the atomic radius, you must take into account two definitions:
- the shielding is the effect that the innermost electrons cause on the outermost electron. The electron is subjected to the attractive force coming from the nucleus and the repulsive force due to the other electrons that the atom has. When these electrons are in more internal orbitals the effect is greater than when they reside in orbitals as external as that of the electron they repel. That is, the shielding consists of the repulsion between the electrons, which decreases the attraction of the nucleus.
- The effective nuclear charge is the charge that the nucleus should have so that, in the absence of other electrons, the attraction of the nucleus on the considered electron would be the same as the net attraction that the electron experiences in the real atom.
- Relation between electron affinity and atomic radius
Electron affinity increases from left to right, and from bottom to top in the periodic table.
As you move to the right in the same period of the periodic table, even though the atomic number increases and, therefore, the number of electrons also increases, the atomic radius decreases.
This is because, as the number of protons in the nucleus increases, the effective nuclear charge is increasing, and for this reason the nucleus attracts electrons with greater intensity.
Then, as it moves over a period to the right, due to the increase in the effective nuclear charge, the closer to the nucleus the new incorporated electron will be found, so it will be attracted more strongly.
Electron affinity increases from left to right, and from bottom to top in the periodic table.
In the case of a group, the electron affinity increases upwards, because the higher atoms are smaller (they have a smaller atomic radius) and will attract the new incorporated electron more strongly, being the most favorable process for these atoms.
- Summary
Electron affinity increases from left to right, and from bottom to top in the periodic table, in the opposite direction to the atomic radius.
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