Question

3. The 1st ionization energy of group 1 elements are shown below. Element IE1 (eV) 5.2 Na 5.1 4.3 Rb Cs Fr Element 119 4.2 3.9 4.1 4.9 (calculated) (a) (2 points) Rationalize the decrease observed on moving from Li to Cs. b) (2 points) Rationalize the increase observed on moving from Cs to Element 119.

Answer 1

1st ionisation enengy decreases on moving from @ The ti to os. to remove valence shell of an atom. So lonization rically depends on the attraction The lonization energy is the enengy required to an electrow from the valence shell of an at enengy of an atom basically depends on the between the positive changed nuclers and negatively changed valence electrons of the atom. As we move from Li to es, the size of the atoms increases, Thus the attraction between the positively charged nuclers and negatively charged valence electrons gradually decreases. Therefore the valence electrons can be remove easily. Consequently the Ionization energy of the atom decreases. 6 Moving from es to element 119, the 1st conization energy increases. This is due to the fact that the size on atomic nadie of the atom from es to element 119 decreases. Because of the lanthanide contraction. The lanthanide contraction effect anises due to the poor shielding of the 46 electrons. The electrons occupied in 48 orbital can't shield the outer shell electrons effectively, a es to element 119, the positively changed nudlery ho

a greaten attraction the valence electrons they the size of the atom decreases from es to element 119. Consequenty the removal of electrons from valence shell become tough. So the ionization energy of the atom from es to element 119 increases.