Page 1 :
Electron Gain Enthalpy, When an electron is added to a neutral gaseous atom (X) to, convert it into a negative ion, the enthalpy change accompanying the, process is defined as the Electron Gain Enthalpy or Electron Affinity, Electron gain enthalpy provides a measure of the ease with which, an atom adds an electron to form anion as represented by equation, , , X(g) + e X-(g)+ energy, (electron gain enthalpy), , Energy is released when an electron is added to the atom and the, electron gain enthalpy is negative.
Page 2 :
Factors Affecting Electron Gain Enthalpy, Effective Nuclear Charge (ENC), With increase in ENC, the force of attraction exerted by the nucleus, on the electrons increases. Consequently, the atom has a greater, tendency to attract additional electron i.e., its EGE increases i.e., become more negative., Atomic Size, With decrease in size ENC increases & hence EGE increases., , Electronic Configuration, The value of EGE depends effectively upon electronic configuration, of elements, elements with stable electronic configuration posses, lower (less -ve) value of EGE
Page 3 :
Periodic Trend, In A Period, The EGE increases i.e. become more negative as we move, across a period because the atomic size decreases and hence, the force of attraction exerted by the nucleus on the electrons, increases. Consequently, the atom has a greater tendency to, attract additional electron i.e., its electron affinity increases, In A Group, The EGE decreases (-) vely because the atomic size increases, and therefore, the effective nuclear attraction decreases and, thus electron affinity decreases
Page 4 :
Important Questions, Noble gases have practically zero or +ve EGEs., This is because they have no tendency to gain an additional, electron as they already have the stable ns2np6 configuration, Halogens have high electron affinities., This is due to their strong tendency to gain an additional electron, to change into the stable ns2np6 configuration.
Page 5 :
Important Questions, Explain why, (a) electron gain enthalpy of F is less than that of the Cl., The electron gain enthalpy of F (1s2 2s2 2p5) is less than that of the, succeeding element. This is because when an electron is added to F,, the added electron goes to the smaller (n= 2) quantum level and, suffers significant repulsion from the other electrons present in this, level, , For the n = 3 quantum level (Cl ), the added electron occupies a larger, region of space and the electron-electron repulsion is much less.
Page 6 :
Electronegativity, The tendency of an element in a molecule to attract the shared pair, of electrons towards itself is known as electronegativity, It is measured on Pauling scale in which F is most electronegative, In a Period- On moving across a period left to right, Z and Z* increases, number of shells remains constant, atomic radius decreases, force of attraction between shared electron and, nucleus increases, Hence electronegativity increases along a period
