Elements in the Periodic Table often show periodic trends. Describe and explain the periodic trend in atomic radius and electronegativity from Na to Cl.

Atomic Radius - As you go across the Periodic Table from left to right, the atomic radius decreases. This is because the electrons are added to the same shell and as you move from left to right. At the same time, the proton number increases. The increasing proton number has a greater effect than increasing electron number, therefore causing a greater attraction between the positively charged nucleus and the electrons in the outer shell, decreasing the radius of the atom. Electronegativity - As you go down a group the electronegativity decreases. This is because there is a greater atomic radius (and therefore less attraction). As you do across a period, the electronegativity increases. If a valence shell is half full, it is easier to gain an electron than lose one.