When comparing boron and carbon, one might expect boron to have a larger atomic radius than carbon. However, the atomic radius of these elements provides a different insight.
Boron (atomic number 5) is situated in group 13 of the periodic table, whereas carbon (atomic number 6) is located in group 14. As you move from left to right across a period, the atomic radius typically decreases. This is due to the increase in positive charge in the nucleus, which pulls the electrons in closer.
Despite boron being positioned one period above carbon, it doesn’t directly correlate to a larger atomic radius. In fact, carbon, being one position to the right of boron in the periodic table, experiences a stronger nuclear charge pulling its electrons closer, thus resulting in a smaller atomic radius.
Therefore, we can conclude that carbon has a smaller atomic radius than boron, contrary to what one might initially think. The expected trend is that atomic radii decrease across a period, leading us to understand that carbon, having a higher nuclear charge with more protons, will hold its electrons more tightly compared to boron.