Which of the following options lists the elements in order of INCREASING atomic radius?
- a. Fluorine, Germanium, Gold
- b. Hydrogen, Lithium, Beryllium
- c. Carbon, Nitrogen, Oxygen
- d. Bromine, Chlorine, Fluorine
The elements are very conveniently arranged in the periodic table for determination of similarity in chemical properties and changes in atomic radius. If we go down a group, we find that the atomic radius increases, while moving along a period (from left to right), the radius decreases. Thus, the easiest way to find the order of increasing atomic radius is to find the elements' relative position in the periodic table.
A) F, Ge, Au: Since all these elements exist in different groups and periods, one can check the atomic radii to be totally sure. The atomic radii of these elements are 42 pm, 125 pm and 174 pm. Hence they are arranged in order of increasing radius.
B) H, Li, Be: Li and Be exist in the same period and Be is to the right of Li and hence Li has more atomic radius than Be. Thus, this series is not arranged in increasing order of atomic radius.
C) C, N, O: Carbon, Nitrogen and Oxygen are placed in the periodic table in this very order, i.e. from left to right in the same period. That is, atomic radius will decrease as we move from C to O. Hence this series is actually arranged in decreasing order of atomic radius.
D) Br, Cl, F: In the periodic table, as we move down the halides, the elements are arranged as F, Cl, Br, etc. Here the series is reversed and hence they are arranged in order of decreasing atomic radius.
Thus, only option A is arranged in increasing order of atomic radius.
Hope this helps.