249 6 Periodic Ex Ans

249 6 Periodic Ex Ans - 249 College Chemistry I The...

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249 College Chemistry I  The Periodic Table - Exercise 1. Arrange the size of the following ions in ascending order: N 3- , F - , Mg 2+ , Ca 2+ , Fe 2+ and Fe 3+ . Mg 2+ ~ Fe 3+ < Fe 2+ < Ca 2+ < F - < N 3-   2. Main group elements show a considerable change in properties on moving across a period, while all elements in the first row of d-block elements share similar properties. (a) By using Slater’s rules, calculate the effective nuclear charge ( Z* ) felt by the valence electron of Na and Cl respectively. Na: [1s2][2s22p6] [ 3s1 ] Z* = Z – S = 11 – [0 x 0.35 + 8 x 0.85 + 2 x 1.0] = 11 – 8.8 = 2.2 Cl: [1s2][2s22p6] [3s2 3p5 ] Z* = Z – S = 17 – [6 x 0.35 + 8 x 0.85 + 2 x 1.0] = 17 – 10.9 = 6.1 (b) Also calculate the effective nuclear change ( Z* ) felt by the valence e- of Cr and Zn respectively. Cr: [1s2][2s22p6] [3s23p6][3d5][ 4s1 ] Z* = Z – S = 2.95 Zn: [1s2][2s22p6] [3s23p6][3d10][ 4s2 ] Z* = Z – S = 30 – 25.65 = 4.35 249/The Periodic Table Ex 1
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(c) What is the relationship between effective nuclear charge ( Z* ) and ionization enthalpy (I.E.)? Ionization enthalpy increases as effective nuclear charge increases. (d) On the same diagram, sketch the 1st I.E. of main group elements from Na to Ar and that of d-block elements from Sc to Zn. Hence, comment on any difference in the trends of I.E. Moving across the 1 st transition period, electrons are added to 3d orbitals which shield effectively the 4s electrons (valence electron) from the nuclear charge the increase in nuclear charge has effectively shielded. A rather constant effective nuclear charge is experienced by the outermost electrons.
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This note was uploaded on 02/22/2012 for the course CHEM yscn0027 taught by Professor Drtong during the Fall '10 term at HKU.

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249 6 Periodic Ex Ans - 249 College Chemistry I The...

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