Elements X, Y and Z have atomic numbers 19, 37 and 55 respectively. Which of the following statements is true about them?
(a) Their ionization potential would increase with increasing atomic number
(b) ‘Y’ would have an ionisation potential between those of ‘X’ and ‘Z’
(c) ‘Z’ would have the highest ionization potential
(d) ‘Y’ would have the highest ionization potential.
Correct answer: (b) ‘Y’ would have an ionisation potential between those of ‘X’ and ‘Z’
Explanation:
Elements X, Y, Z with atomic numbers 19, 37, 55 lie in group 1 (alkali metals). On moving down a group from the size of atoms increases, the outermost electrons become less strongly held. So the ionization energy decreases. Therefore, IE of Y could be between those of X and Z.
X - Y - Z
K(19) - Rb(37) - Cs(55)
I.E. 4.3 - 4.2 - 3.9