M(g)<\/sub> + e–\u00a0<\/sup>\u2192 M–<\/sup>(g)<\/sub>\u00a0\u00a0 \u00a0 \u00a0\u00a0EA<\/strong><\/p>\n Since one, two or more electrons can be added to form an anion, many types of electron affinity is possible.<\/p>\n M(g)<\/sub> + e–\u00a0<\/sup>\u2192 M–<\/sup>(g)<\/sub>\u00a0\u00a0 \u00a0\u00a0<\/sup>EA1<\/sub><\/strong><\/p>\n M–<\/sup>(g)<\/sub>\u00a0+ e–\u00a0<\/sup>\u2192 M2-<\/sup>(g)<\/sub>\u00a0 \u00a0\u00a0<\/sup>EA2<\/sub><\/strong><\/p>\n M2-<\/sup>(g)<\/sub> + e–\u00a0<\/sup>\u2192 M3<\/sup>–<\/sup>(g)<\/sub>\u00a0 \u00a0\u00a0<\/sup>EA3<\/strong><\/p>\n The second electron affinity (EA2<\/sub><\/strong>) is always larger than the first electron affinity (EA1<\/sub><\/strong>) as it is hard to add an electron into a negative ion than a neutral atom. As for example the electron affinity of oxygen to add two electrons are:<\/p>\n O(g)<\/sub> + e–\u00a0<\/sup>\u2192 O–<\/sup>(g)<\/sub>\u00a0\u00a0 \u00a0\u00a0<\/sup>EA1<\/sub><\/strong> = -142 Kj mol-1<\/sup><\/p>\n O–<\/sup>(g)<\/sub>\u00a0+ e–\u00a0<\/sup>\u2192 O2-<\/sup>(g)<\/sub>\u00a0 \u00a0\u00a0<\/sup>EA2<\/sub><\/strong> = + 844 Kj mol-1<\/sup><\/p>\n Here we can see that the second electron affinity is much higher than the first one. Thus in general successive electron affinity increase in magnitude\u00a0EA1<\/sub><\/strong><EA2<\/sub><\/strong><EA3<\/sub><\/strong>\u00a0<\/sub><\/strong>and so on.<\/p>\n The first electron affinity of elements in the periodic table increases across the period and decreases down the group.<\/p>\n Moving from left to right across a period, the number of protons and electrons increases while the number of energy shells stay same. Thus the affinity of an element (or more positive nucleus) to an electron increases across the period.<\/p>\n Moving down a group, the number of energy shells also increases with the increase of protons and electrons. So because of shielding effects of electrons in the increased inner shells, the affinity to an electron of the nucleus is reduced down the group.<\/p>\n According to the above discussion, fluorine should have more electron affinity than chlorine. But the electron affinity of fluorine is less than chlorine. As fluorine is the smallest atom in this group, entering an electron to it results a greater repulsion because of the existence of electron cloud in the small shell. As a result, electron affinity decreases in fluorine.<\/p>\n Nitrogen has very low electron affinity because of its half filled orbitals. The nitrogen is fairly stable atom than adjacent atom carbon in the periodic table. Thus the electron affinity falls from carbon to nitrogen.<\/p>\n\n
Order of successive electron affinity<\/h3>\n
First electron affinity in the periodic table<\/h2>\n
![\"Cdang](\"https:\/\/upload.wikimedia.org\/wikipedia\/commons\/f\/f1\/Electron_affinity_periodic_table.svg\")
<\/p>\nFirst electron affinity increases across the period<\/h3>\n
First electron affinity decreases down the group<\/h3>\n
Fluorine is an exception<\/h4>\n
\n\n
\n F<\/td>\n 1s2<\/sup>2s2<\/sup>2px<\/sub>2<\/sup>2py<\/sub>2<\/sup>2pz<\/sub>1<\/sup><\/td>\n EA1<\/sub><\/strong> = -328 kJ mol-1<\/sup><\/td>\n<\/tr>\n \n Cl<\/td>\n 1s2<\/sup>2s2<\/sup>2p6<\/sup>3s2<\/sup>3px<\/sub>2<\/sup>3py<\/sub>2<\/sup>3pz<\/sub>1<\/sup><\/td>\n EA1<\/sub><\/strong> = -349 kJ mol-1<\/sup><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Nitrogen is an exception<\/h4>\n