Atomis Radius Trend

[Jamie Hsu]

If we are comparing the radius of an atom on the very right side of the periodic table (group 17, period 3) with an atom on the left side of the periodic table (group 2, period 4) how should we compare the size of the atomic radius if they are in different groups and their periods are next to each other? Should we look at the group or period first?

What happens if we are asked to rank an ion like Br-, which has the number of electrons to be in group 18? Do noble gases have radius?

[Camille Marangi 2E]

I think the appropriate strategy is just to remember that atomic radii decrease across a period and increase down a group. So for this specific issue, with each additional period down the periodic table an energy level is added and the atomic radius grows by an entire shell. Elements on the left side of the table are typically larger than the right side due to their smaller effective nuclear charge and in this case will be doubly larger due to the increase in period. Anions have ionic radii which have their own set of rules. Each additional electron increases the radius due to electron-electron repulsions.

[Tinisha 1G]

Use the periodic trends of atomic radii, and why this is what it is, to formulate your answer. As we go towards the right of the periodic table, the effective nuclear charge increases, and therefore, has a stronger pull on the electrons, making the radius of the atom smaller. As we go down the periodic table, the atomic radius decreases because you are adding an extra shell every time you go down one period, therefore making the atomic radius bigger.