Inorganic chemistry (Gary L. Miessler)
풀었던 부분만 올립니다
(쪽수: 번역판 기준)
p. 56 Example 3.1
SCN-
In the thiocyanate ion, SCN-, three resonance structures are consistent with the electron-dot method, as shown in Fig 3.3. Structure A has only negative formal charge on the nitrogen atom, the most electronegative atom in the ion. Structure B has a single negative charge on the S, which is less electronegative than N. Structure C has charges of 2- on N and 1+ on S, consistent with the relative electronegativities of these atoms but also has a large magnitude 2- charge and greater charge separation than the other structures. Therefore these structures lead to the prediction that structure A contributes the most to the electronic ground state of SCN-, structure B contributes an intermediate amount, and any contribution from C is minor in describing the electroninc ground state of SCN-.
The bond lengths in Table 3.1 are somewhat consistend with this conclusion, with SCN- bond lengths between those of structures A and B. Protonation of the ion forms HNCS, consistent with a negative charge on N in SCN-. The bond lengths in HNCS are close to those of double bonds, consistent with the structure H-N=C=S.
p.56 Example 3.2
The isoelectronic cyanate ion, OCN- has the same possibilities, but the larger electronegativity of O is expected to make structure B contribute more to the electronic ground state in cyanate relative the contribution of B in thiocyanate. The protonation of cyanate results in two isomers, 97% HNCO and 3% HOCN, consistent with a major contribution of structure A and a small, but significant, contribution from B. The bond lengths in OCN- and HNCO in Table 3.2 are reasonably consistent with this analysis. Formal charge arguments provide a good starting point to assess Lewis structures, and reactivity patterns are also useful to gain experimental insight about electron distributions.
p.57 Example 3.3
CNO-
The isometric fulminate ion, CNO-, can be drawn with three silimar structures, but the resulting formal charges ahve larger magnitudes than in OCN-. Because the order of electronegativities is C<N<O, node of there are ideal structures, and it is not surprising that this ion is unstable. THe only common fulminate salts are of mercury and silver; both are explosive. Fulminic acid is linear HCNO in the vapor phase, consistent with the greatest contribution from the structure C; coordination complexes of CNO- with transition-metal ions are known with MCNO structures.
p.57 Exercise 3.1
Use electron-dot diagrams and formal charges to predict the bond order for each bond in POF3, SOF4, and SO3F-
풀이:
(a) POF3 : The octet rule resuts in single P-F and P-O bonds; formal charge arguments resut in a double bond for P=O. The actual distance is 143 pm, considerbly shorter than a regular P-O bond (164 pm)
(b) SOF4: This is a distorted trigonal bipyramidal structure, with an S=O double bond and S-F single bonds required by formal charge arguments. The short S=O bond length of 141 pm is in agreement.
(c) SO3F-: This is basically a tetrahedral structure, with two double bonds to oxygen atoms and single bonds to fluorine and the third oxygen. The S-O bond order is then 1.67 and the bond length is 143 pm, shorter than the 149 pm of SO4 2-, which has a bond order of 1.4.
p.65 Example 3.4
SbF4-
SF5-
SeF3+
풀이:
1) SbF4- : havs a single lone pair on Sb. Its structure is therefore similar to SF4, with a lone pair occupying an equatorial position. This lone pair causes considerable distortion, giving an F-Sb-F (axial positions) angle of 155˚ and an F-Sb-F (equitorial) angle of 90 ˚
2) SF5- have a single lone pair. Its structure is based on an octahedron, with the ion distorted away from the lone pair, as in IF5.
3) SeF3+ has a single lone pair. This lone pair reduces the Se-F bond angle significantly, to 94˚
p.65 Exercise 3.2 Predict the structures of the following ions. Include a description of distortions from the ideal angles (for example, less than 109.5˚ because...).
NH2 -, NH4 +, I3-, PCl6-
풀이:
p. 65 Example 3.5
1) HCP
2) IOF4 -
3) SeOCl2
해설:
1) HCP : like HCN, is linear, with a triple bond:
2) IOF4-: has a single lone pair on the side opposite the oxygen.
The lone pair has a slightly greater repulsive effect than the double bond to oxygen
- as shown by the average O-I-F angle of 89도
- The extra repulsive character of the I=O bond places it opposite the lone pair
3) SeOCl2 : has both a lone pair and a selenium-oxygen double bond
- The lone pair has a greater effect than the double bond
- the Cl-Se-Cl angle is reduced to 97도 by this effect, and the Cl-Se-O angle is 106도
p.65 Exercise 3.3
Predict the structures of the following. Indicate the direction of distortions from the regular structures
