Generally, nonmetals have more positive Eea than metals. Atoms, such as Group 7 elements, whose anions are more stable than neutral atoms have a higher Eea.
Atoms of group 17 gain one electron and form anions with a 1− charge; atoms of group 16 gain two electrons and form ions with a 2− charge, and so on.
There are, however, two major exceptions to this trend: The electron affinities of elements B through F in the second row of the periodic table are less negative than those of the elements immediately below them in the third row.
Group 4 elements have 4 valence electrons. The non-metals in this family react by gaining 4 extra electrons through the formation of covalent bonds (sharing bonds).
Trends in Atomic Radius of Group 2 Elements
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Halogens are highly reactive nonmetal elements in group 17 of the periodic table. Halogens include solids, liquids, and gases at room temperature, and they vary in color. Halogens are among the most reactive of all elements.
Unlike electronegativity, electron affinity is a quantitative measurement of the energy change that occurs when an electron is added to a neutral gas atom. The more negative the electron affinity value, the higher an atom’s affinity for electrons.
Chlorine has the most negative electron affinity. According to Wikipedia [Electron affinity], In chemistry and atomic physics, the electron affinity of an atom or molecule is defined as the amount of energy released when an electron is added to a neutral atom or molecule in the gaseous state to form a negative ion.
This is because Group 2 elements already have a full valence s shell and the addition of a new electron would move to the higher energy p shell that is otherwise left empty in the neutral atom. Because of electron – electron repulsions, this is energetically unfavorable, making the electron affinity more positive.
Thus, O − has the highest electron affinity.
The electron affinity is defined as the energy change that occurs when an atom gains an electron, releasing energy in the process. If a reaction is exothermic, the change in energy is negative. This means that the electron affinity is positive.
Noble gases have maximum electron affinity.