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CHM 113 Lecture Notes - Core Electron, Fluorine, Electron Configuration

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6 Dec 2012

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Document Summary

Valence electrons (ve): an electron that resides in outermost shell of an atom. Fluorine (9e-): 1s22s22p5: 1s2: n=1, 2s22p5: n=2, 7 ve"s. Number of ve equals group number on periodic table: halogens: 7 ve, o, s, etc: 6 ve, alkaline medals (na, k): 1 ve, noble gases: 8 ve (except he, which has 2) [ne] 3s2: 2 ve (n=3, 10 core electrons, 12 protons in nucleus. Electrons attracted by protons in nucleus (but not all equally) Ve are shielded from nucleus by core electrons. Ve are shielded from nucleus by other ve (only weakly) Zeff: net positive charge that an electron sees from the nucleus: zeff = z s, z represents number of protons in nucleus, s represents the number of shield (core) electrons. Trends in zeff experienced by ves: as you go from left to right on a row, zeff increases.

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Related Questions

Slater’s rules are a way to estimate the effective nuclear charge experienced by an electron. In this approach, the “shielding constant,” S, is calculated. The effective nuclear charge is then the difference between S and the atomic number, Z.

The shielding constant, S, is calculated using the following rules:

(1) The electrons of an atom are grouped as follows: (1s) (2s, 2p) (3s, 3p) (3d) (4s, 4p) (4d), and so on.

(2) Electrons in higher groups (to the right) do not shield those in the lower groups.

(3) For ns and np valence electrons

a) Electrons in the same ns, np group contribute 0.35 (for 1s 0.30 works better).

b) Electrons in n − 1 groups contribute 0.85.

c) Electrons in n − 2 groups (and lower) contribute 1.00.

(4) For nd and nf electrons, electrons in the same nd or nf group contribute 0.35, and those in groups to the left contribute 1.00.

As an example, let us calculate Z* for the outermost electron of oxygen:

Here is the calculation for a d electron in Ni:

and for an s electron Ni:

(Here 3s, 3p, and 3d electrons are in the (n − 1) groups.)

a) Calculate Z* for F and Ne. Relate the Z* values for O, F, and Ne to their relative atomic radii and ionization energies.

b) Calculate Z* for one of the 3d electrons of Mn, and compare this with Z* for one of the 4s electrons of the element. Do the Z* values give us some insight into the ionization of Mn to give the cation?