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PLEASE please DEFINE and explain how and why effective nuclear charge trends the way that it does across the periodic table.

User Junior
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1 Answer

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Effective nuclear charge decreases down a group and increases from left to the right across a period.

Effective nuclear charge decreases down a group because as you go down a group, there are more shells of electrons. This means that the distance between the nucleus and the outermost electron orbital increases; thus the attraction of the valence electrons to the nucleus decreases down a group.

Effective nuclear charge increases from left to right across a period because although electron shielding remains constant, the number of protons in the nucleus remains constant. This means that the nucleus has a greater positive charge, and thus there is a greater attraction between the electrons in the electron cloud and the nucleus (since opposite charges attract).

User Siddhusingh
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