In a period, do the number of shielding electrons change? Why do you think atomic radius decreases across a

period?

The more energy levels an atom has, the more shielding electrons that atom has. Do you think this affects atomic radius, if so how? Does it affect electronegativity, if so how?

Here's what I find.

Explanation:

(a) Atomic radius

The number of inner electrons does not change, so their shielding does not change.

However, the number of protons increases, so the effective nuclear charge (ENC) - the charge felt by a valence electron - increases, and the valence electrons are pulled closer to the nucleus.

The atomic radius decreases because of the increasing ENC.

(b) Atomic radius and electronegativity

As you go from top to bottom within a Group of the Periodic Table, you are adding more electron energy levels, so the atom gets bigger. The atomic radius increases.

The number of valence electrons stays the same, but they are increasingly shielded and further away from the nucleus.

The electrons in a shared bond are less attracted to their nuclei, so the electronegativity decreases.