# Periodic Trends of Zeff and Electronegativity

The effective nuclear charge $Z_\mathrm{eff}$ increases from left to right and from top to bottom. Can you explain why it increases from top to bottom?

Also can we explain the periodic trend of electronegativity using the shielding effect?

EDIT: The calculation of $Z_\mathrm{eff}$ for Li would be 1 (3 protons − 2 core electrons). For Na is 1 (11 protons − 10 core electrons). So far it doesn't seem to me that $Z_\mathrm{eff}$ should increase from top to bottom. Considering the fact though that for Na there are more electrons shielding the only valence electron than Li as well as Na's electron is relatively more distant than that of Li, the first should be experiencing less $Z_\mathrm{eff}$. This is not true however. As far electronegativity is concerned I can't come up with a neat explanation.

• Looks like homework to me. Can you share what work you've done while working towards an answer? – Todd Minehardt Aug 7 '15 at 21:01
• Your misconception: Shielding by core electrons is perfect. Truth: shielding for Li is less than 2, shielding for Na is less than 10. – orthocresol Aug 8 '15 at 18:05