Across a period from left to right, the atomic radius of the elements generally
- A. decreases, because nuclear charge increases while electrons enter the same shell
- B. increases, because more electrons are added
- C. stays the same
- D. increases, because the nuclear charge decreases
Explanation
Each successive element adds one proton and one electron, but the electron enters the same outermost shell, so shielding hardly changes while the effective nuclear charge rises and the shell is pulled inwards. Down a group the opposite happens, since a whole new shell is added and radius increases. Atomic radius is the single trend from which ionisation energy and electronegativity mostly follow.