Question

according to periodic trends, which period 3 element would have the lowest atomic radius?
ar
na
mg
cl

1. use a periodic table to choose the best answer.

which of these elements as the smallest atomic radius?
li
be

1. use a periodic table to choose the best answer.

which of these elements has the largest atomic radius?
n
p

Explanation:

• For the first question:
• Atomic radius decreases across a period (from left to right) in the periodic table.
• Period 3 elements: Na (Group 1), Mg (Group 2), Cl (Group 17), Ar (Group 18).
• As we move from left (Na) to right (Ar), atomic radius decreases. But Ar is a noble gas and has a larger atomic radius than Cl due to its full - filled electron shell and different measurement (van der Waals radius). So Cl has the lowest atomic radius among the given period 3 elements.
• For the second question:
• Atomic radius increases down a group.
• Li (Period 2, Group 1) and Be (Period 2, Group 2). Since Be is to the right of Li in the same period, Li has a larger atomic radius than Be.
• For the third question:
• Atomic radius increases down a group.
• N (Period 2, Group 15) and P (Period 3, Group 15). Since P is in a lower period (has more electron shells), P has a larger atomic radius than N.

Answer:

• First question: Cl
• Second question: Li
• Third question: P