Z effective

[Ian_Lee_1E]

What does it mean for electrons of an atom to be more effective than the other?

[Benjamin_Hugh_3F]

It refers to the effective nuclear charge, so if an electron has a more effective nuclear charge than others, it means it causes greater attraction, pulling the electrons closer to the nucleus.

[Ria Nawathe 1C]

The effective nuclear charge refers to the protons/nucleus of an atom, not the electrons. In terms of periodic trends, the effective nuclear charge increases as you go across a period because the atomic number increases and electrons are being added to the same energy level. It decreases down a group because the atomic radius, number of energy levels, and number of electrons increases, leading to the shielding effect and electron-electron repulsion.