* Periodic Trends: Atomic radius generally increases as you move down a group (column) of the periodic table and decreases as you move across a period (row) from left to right.
* Location on the Periodic Table: Bromine is located in Group 17 (halogens) and arsenic is in Group 15 (pnictogens). Both are in the same period (period 4).
* Effective Nuclear Charge: Bromine has a higher effective nuclear charge (the net positive charge experienced by an electron) than arsenic. This is because bromine has more protons in its nucleus, pulling its electrons more tightly and resulting in a smaller atomic radius.
In summary: Although bromine and arsenic are in the same period, bromine's higher effective nuclear charge due to its greater number of protons leads to a smaller atomic radius.
