Effective Nuclear Charge

What is the definition of effective nuclear charge (Zeff)?

The amount of positive charge experienced by an electron, reduced by the shielding effect of lower orbital electrons.

How does effective nuclear charge change across a period?

It increases from left to right across a period.

Why does effective nuclear charge increase from left to right across a period?

The number of protons increases without an increase in electron shells, resulting in a stronger pull on the electrons.

How does effective nuclear charge change within a group?

It increases going up a group.

Why does effective nuclear charge increase going up a group?

The number of electron shells decreases, bringing outer electrons closer to the nucleus and increasing the nuclear attraction.