Kushal said:period 3 elements have SMALLER electron affinities than period 2 elements for the reasons above. But an exception is F(period 2) and Cl(period 3). This is due to the fact that F has a very small size...
Hope i helped you
ritwik06 said:Why is electron affinity negative?
In my book its written, that on moving down a group, tit decreases. But why is it that period 3 elements have greater E.A. than period 2 elements?
Kushal said:you should precise which E.A.! The first E.A. is the amount of energy released when 1 mol of a gaseous atom accepts 1 mol electrons. the first E.A. is always negative. E.A. is in fact an energy change; when an energy change is -ve, it implies that the reaction is exothermic, i.e energy is liberated...and when energy change is +ve, it implies that the reaction is endothermic, i.e energy is absorbed. right
the attraction between the nucleus and the first electron to be accepted releases energy. the second E.A. and succeeding ones are all endothermic. this is because energy is needed to force the electron into the atom. energy is now required as the second incoming electron is being at the same time attracted by the nucleus and repelled(to a larger extent) by the other electrons of the atom. right
E.A. decreases down a group. this is because, down a group the atoms become shielded by the larger numbers of electrons. (e.g. Li has 3 e-, Na has 11e-, K has 19e-,...) the shielding decreases the attractive force of the nucleus on the incoming electron and furthermore, the incoming electron is being repelled at a greater extent by the larger number of electrons. i.e more energy is required to force that electron into the atom.
period 3 elements have SMALLER electron affinities than period 2 elements for the reasons above. But an exception is F(period 2) and Cl(period 3). This is due to the fact that F has a very small size...
Hope i helped you
TripleS said:how is that an exception?...doesnt F have a greater E.A than Cl?
Nope. Though F is more electronegative than Cl, E.A of F is less than Cl. It is because F is comparatively very small atom which give it higher electron density than it's neighbours. If you want to place an electron in it's (F)outermost shell you have to do some extra work (for the extra density of electrons it has). So overall it effects the net realease of energy.
Electron affinity is the amount of energy released when an atom gains an electron. In period 2 and 3 elements, the electron affinity is negative because these elements have a relatively small atomic radius and a high effective nuclear charge. This means that the added electron experiences a strong attraction from the nucleus, making it difficult to add an electron and resulting in a negative electron affinity value.
The atomic radius is the distance from the nucleus to the outermost electron. In period 2 and 3 elements, the atomic radius is relatively small, which means that the added electron is closer to the nucleus and experiences a stronger attraction. This makes it more difficult to add an electron, resulting in a negative electron affinity value.
No, not all elements in period 2 and 3 have negative electron affinity. While most elements in these periods do have negative electron affinity values, there are exceptions such as nitrogen and neon, which have slightly positive values. This is due to their stable electron configurations, making it more difficult to add an electron.
Effective nuclear charge is the net positive charge experienced by an electron in an atom. In period 2 and 3 elements, the effective nuclear charge is high due to the increasing number of protons in the nucleus. This strong attraction between the nucleus and the added electron makes it difficult to add an electron, resulting in a negative electron affinity value.
Electron affinity is an important concept in understanding the reactivity of elements. Elements with high electron affinity tend to be more reactive and are more likely to form chemical bonds with other elements to achieve a stable electron configuration. It is also used to predict the stability of ions and the formation of ionic compounds.