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quiz2key - each other's charge very well so the increasing...

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CHEMISTRY 131 Quiz #2 Friday, February 3, 2006 Name: ___________________________________________ 1. Use Slater's rules to calculate the effective nuclear charge for the 3d and 4s electrons in Zn. Using your answer, briefly explain why Zn tends to form +1 and +2 ions, but not +3 or higher. (7 points) (1s 2 )(2s 2 2p 6 )(3s 2 3p 6 )(3d 10 )(4s 2 ) 3d: (9 x 0.35) + (18 x 1.00) = s = 21.15 Z* = 30 – 21.15 = +8.85 4s: (1 x 0.35) + (18 x 0.85) + (10 x 1.00) = s = 25.65 Z* = 30 – 25.65 = +4.35 It is relatively easy to remove the first two electrons in Zn, to form +1 and +2 ions. They come from the 4s orbital, where the effective nuclear charge is relatively small. But it suddenly becomes much more difficult to remove the third electron because the effective nuclear charge is so much larger in the 3d orbital. 2. Why is the effective nuclear charge experienced by the 3d electrons in Zn expected to be larger than for the 3d electrons in Ni? (3 points) Electrons in the same shell are added at approximately the same distance from the nucleus and therefore don't screen
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Unformatted text preview: each other's charge very well, so the increasing number of protons makes a big difference. This is what is happening when we go across a row of the periodic table. Zn has 2 more protons than Ni; it also has 2 more electrons, but since those electrons are added to the same shell (they don't add to the core), they do not screen those 2 additional protons very much. So, the effective nuclear charge of Zn is expected to be larger. Bonus. What is Hund's Rule? (1 point) Hund's Rule states that, due primarily to electronic repulsions, since electrons have the same charge, they will occupy individual orbitals at the same energy before they pair up in the same orbital. For example, if there are three p orbitals at the same energy but with different orientations, electrons will occupy them individually because otherwise there would be too much charge building up in the same orbital (the same region of space)....
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