Video Transcript
The periodic table below shows a
highlighted row of elements, from sodium to argon. How does the atomic radius change
when moving from sodium to argon? (A) It does not change. (B) It increases. (C) It decreases. (D) It alternates between
increasing and decreasing.
This question is asking us to
determine how the atomic radius changes when moving across a row in the periodic
table. The atomic radius describes the
size of an atom. As we move across a row in the
periodic table from left to right, there’s an increasing number of protons and
electrons in an atom. But that doesn’t mean the size of
the atom increases.
As we move across a row, all of the
electrons are added to the same energy level. At the same time, the number of
protons in the nucleus is increasing, which means there’s more positively charged
particles in the nucleus. Since there are more positively
charged particles in the nucleus, the strength of the attraction between the nucleus
and outer electrons increases. This means that the outer electrons
are being pulled closer to the nucleus, which has the effect of decreasing the size
of the atom. So the atomic radius decreases
across a row in the periodic table.
So, to answer the question, as we
move across the highlighted row of elements from sodium to argon, the atomic radius
decreases. Answer choice (C) is the correct
answer.
