Question

which element will have the largest atomic radius?
periodic table with some elements highlighted: cl (row 3, column 7), as (row 4, column 5), tl (row 6, column 3), fr (row 7, column 1)
options:
thallium (tl)
arsenic (as)
chlorine (cl)
francium (fr)

Explanation:

Step1: Recall atomic radius trend

Atomic radius increases down a group (vertical column) and decreases across a period (horizontal row) in the periodic table. This is because as we go down a group, the number of electron shells increases, so the distance from the nucleus to the outermost electrons increases. Across a period, electrons are added to the same shell, and the increasing nuclear charge pulls the electrons closer, decreasing the radius.

Step2: Analyze positions of elements

• Thallium (Tl) is in period 6, group 13.
• Arsenic (As) is in period 4, group 15.
• Chlorine (Cl) is in period 3, group 17.
• Francium (Fr) is in period 7, group 1.

Among these, Francium (Fr) is in the lowest period (period 7) and also in group 1 (where elements have relatively large radii due to low nuclear charge for the number of shells). Going down the groups, Fr has more electron shells than the others. Also, in group 1, the atomic radius is larger compared to elements in other groups in the same period because the nuclear charge is lower relative to the number of electron shells. So Francium (Fr) will have the largest atomic radius.

Answer:

D. francium (Fr)