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Can someone explain the trend in the periodic table that relates to atomic size again? I just want to make sure that I understand it correctly. I believe that as you go to the right on the periodic table, the atomic size gets smaller. Why is this?
Very simply, as the number of protons increase, the added valence electrons will be pulled toward the nucleus more, which makes the radius smaller. So as you move right on the periodic table, more protons and electrons = greater attraction and smaller radius
As you go down and left across the periodic table, atomic radius will increase. I think the reason the radius increases as you go down is because quantum numbers increase, and therefore valence electrons will begin to occupy higher levels. As the quantum number increases, electrons are held further away from the nucleus, so the radius increases.
Also, as you move right across a period, the increased nuclear charge of the atoms increases pulls the electrons closer to the nucleus, leading to a decreasing size across the period table. Since the number of protons increases across the period, it leads to an increased positive charge of the nucleus, so the electrons are pulled closer to the nucleus because negative and positive charges attract to each other, making the atom smaller.
As you move down the periods, electrons start to occupy higher-level orbitals, so the shielding effect Dr. Lavelle mentioned goes into effect. The outermost electrons are shielded from the full attractive force of the positive nucleus, so there isn't as strong of a pull on the outer layers of electrons. Thus, they aren't as tightly controlled and can exist further from the nucleus, so as period increases, so does atomic nucleus.
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