Screening of the nuclear charge by core electrons in atoms is screening of the nuclear charge by core electrons in atoms is less efficient than that by valence electrons responsible for a general decrease in atomic radius going down a group essentially identical to that by valence electrons more efficient than that by valence electrons both essentially identical to that by valence electrons and responsible for a general decrease in atomic radius going down a group

Screening of the nuclear charge by core electrons in atoms are more efficient than that by valence electrons.

An atom has its nuclear charges contained within the nucleus of the atom. These nuclear charges are positive charges. The protons in the nucleus are positively charged.

The electrons in an atom repel each other. The core electrons repel the valence electrons very strongly thereby preventing them from feeling the attraction of the nuclear charges. This is called screening effect or shielding effect.

The core or inner electrons in atoms are more efficient at this screening effect compared to the valence electrons in the atom.

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