M7Q8: Core and Valence Electrons, Shielding, Zeff – Chem 103/104 Resource Book

Tags

Top Highlights

• electrons in the same valence shell do not block the nuclear attraction experienced by each other as efficiently

• Zeff = Z – S, where S is the number of core electrons that are shielding the valence electrons.

• Shielding is determined by the probability of another electron being between the electron of interest and the nucleus, as well as by the electron–electron repulsions the electron of interest encounters.

• the electron farther away experiences an effective nuclear charge (Zeff).

• The electrons occupying the outermost shell orbital(s) are called valence electrons

• those occupying the inner shell orbitals are called core electrons

• the nuclear charge an electron actually experiences because of shielding from other electrons closer to the nucleus

• the Zeff is always less than the actual nuclear charge, Z.

• Thus, each time we move from one element to the next across a period, Z increases by one, but the shielding increases only slightly. Thus, Zeff for valence electrons increases as we move from left to right across a period.

• Zeff = Z – S, where S is the number of core electrons that are shielding the valence electrons.