This is because these elements have half-filled p-subshells. The values for Group VA elements are less negative (i.e. So, the electron affinity is positive, meaning that the ion will not form. Occupying a higher-energy subshell is energetically unfavorable. The addition of an electron to a noble gas would require that the electron resides in a new, higher-energy subshell. None of the Group llA forms stable negative ions. Instead of releasing energy, the atom would absorb energy. And the added electron will have to go to the n-p orbital of higher energy. The electron affinity values of Group llA metals are positive because they have already completely filled n-s orbitals. The exception mentioned above can be readily explained. Electron affinity values (kJ/ mol) of Some Elements Period 2 By gaining an electron, a halogen atom forms a stable negative ion that has a noble gas configuration.

The halogens, which are one electron shy of a filled p-subshell, have the most negative electron affinities. The elements of Group ITA (Be, Mg, Ca-), Group VA (N, P, As-), and noble gases are exceptions. And thus, the nucleus would have increased attraction for additional electron. Its value generally increases on moving from left to right in a period in the periodic table to decrease in atomic size with the increase of nuclear charge. Periodic Trends (Variation) in a period and in a group. In general, EA value decreases with the increasing atomic radius and increases with the decreased screening effect by the inner electrons.

Therefore, have either zero or very low, electron affinities. Atoms having a stable electronic configuration (i.e., those having completely filled or exactly half-filled outer orbitals) do not show much tendency to add extra electron. Therefore, the electrostatic force of attraction will be more and It will be higher. The smaller the size of the atom smaller will be the distance between the extra electron and the nucleus. Therefore, It increase as the nuclear charge increases. More the nuclear charge of the atom more strongly will it attract an additional electron. The electron affinity of an element depends mainly upon the following factors: The electron affinity of Cl is the most negative of all the elements. The greater the attraction between a given atom and an added electron, theВ more negative the atomвЂ™s electron affinity will be. Small negative numbers indicate that a less stable ion is formed. Large negative numbers such as for Cl -349 kJ/mol indicate that a very stable negative ion is formed. Because 349 kJ/mol are released when an electron is added to Cl(g), the electron affinity, for this convention is +349 kJ/mol. Historically, however, It has been defined as the energy released when an electron is added to a gaseous atom or ion. In most introductoryВ texts, including this one, the thermodynamic sign convention is used.ДЄ negativeВ sign indicates that the addition of an electron is an exothermic process, as in the Note: Two sign conventions are used for electron affinity. Electron affinities similar to ionization potentials are expressed in electron volts or kJ/mol. The formation of 02-(g) from 0(g) can be shown by the following two equations:Д®lectron affinity measures the ease with which an atom gains an electron. This is due to the fact that the addition of an electron to a negative ion must overcome the repulsion due to the existing negative ion, hence the process is endothermic. The addition of a second electron to uni negative ion is an endothermic process. The second electron affinity of an element, M(g) is defined as the amount of energy required to add one more electron to its mono-negative anion, M(g)- to form a negative anion, M2- (g). In addition to the first electron affinity defined above, the second electron affinity of some elements like O, S, and Se is also known. Electron affinity defined above is strictly called the first electron affinity.