# What is the size of boron in relation to oxygen and aluminum?

Jun 10, 2017

Atomic size decreases ACROSS a Period.........

#### Explanation:

Atomic size decreases ACROSS a Period, from left to right as we face the table. And INCREASES down a Group, a column of the Periodic Table. These are very important Periodic Trends that you should try to understand in detail, as they relate directly to atomic structure.

So $\text{2nd row}$ boron is SMALLER than $\text{third row}$ aluminum.

But the $\text{Group 16}$ oxygen atom is SMALLER than the $\text{Group 13}$ boron atom.

I am unwilling to leave it here, in that as physical scientists, we should always interrogate data, and see if the numbers support our (maybe witless) argument.

This site reports that the atomic radii of $B , O ,$ and $A l$ are 125 pm, 85 pm, and 160 pm respectively ($1 \cdot \text{pm} = {10}^{-} 12 \cdot m$). The numbers at least support our argument.

Note that in an exam you would never be expected to remember these data; however, you would be expected to interpret them.