Which atom has a larger atomic radius, Ca or Ra? Why?
Ca is in period 4; it is filling the n= 4 shell.
Ra is in period 7; it is filling the n = 7 shell. Which shell is farther from the nucleus?
To determine which atom, Ca (calcium) or Ra (radium), has a larger atomic radius, we need to compare their positions in the periodic table. The atomic radius generally decreases as we move from left to right across a period (horizontal row) and increases as we move down a group (vertical column).
Calcium (Ca) and Radium (Ra) belong to the same group, Group 2, also known as the alkaline earth metals. Therefore, they have the same number of valence electrons (2) and the general configuration ns^2.
Now, despite belonging to the same group, Ra is located below Ca in the periodic table. Since the atomic radius generally increases as we move down a group due to the additional energy levels being added, we can conclude that Ra has a larger atomic radius compared to Ca.
In summary, Ra has a larger atomic radius than Ca because Ra is located below Ca in the periodic table, and as we move down a group, the atomic radius tends to increase.