6 CHEMICAL BONDING bonds, a neutral nitrogen three(plus one unshared electron pair), and a neutral oxygen two(plus two unshared electron pairs), this gives the Lewis structure shown There are three constitutional isomers of Cho CH, CH, CH,OH CH_ CHCH3 CH, CH,OCH, (c) Four isomers of C4H1oo have-OH groups CHaCH,CH,,OH CH3 CHCH, CH3 CH_ CHCH, OH CH, COH OH Three isomers have c-o-c units. CH3OCH,CH,CH3 CH, CH,OCH, CH CHOCHCH 1. 16 (b) Move electrons from the negatively charged oxygen, as shown by the curved arrows O H O-H The resonance interaction shown for bicarbonate ion is more important than an alternative one involving delocalization of lone-pair electrons in the OH group CO: 0: lot equivalent to original re: not a (c) All three oxygens are equivalent in carbonate ion Either negatively charged oxygen can serve 0: O O: Q Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
bonds, a neutral nitrogen three (plus one unshared electron pair), and a neutral oxygen two (plus two unshared electron pairs), this gives the Lewis structure shown. 1.15 (b) There are three constitutional isomers of C3H8O: (c) Four isomers of C4H10O have @OH groups: Three isomers have C@O@C units: 1.16 (b) Move electrons from the negatively charged oxygen, as shown by the curved arrows. The resonance interaction shown for bicarbonate ion is more important than an alternative one involving delocalization of lone-pair electrons in the OH group. (c) All three oxygens are equivalent in carbonate ion. Either negatively charged oxygen can serve as the donor atom. O O O C O O C O O O C O O C O O O O O C H O O O C H Not equivalent to original structure; not as stable because of charge separation O O O C H O O O C H Equivalent to original structure CH3OCHCH3 CH3 CH3OCH2CH2CH3 CH3CH2OCH2CH3 CH3CH2CH2CH2OH OH CH3CHCH2CH3 CH3CHCH2OH CH3 CH3COH CH3 CH3 CH3CH2OCH3 OH CH3CH2CH2OH CH3CHCH3 Carbamic acid H H N C O H O 6 CHEMICAL BONDING Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
CHEMICAL BONDING (d) Resonance in borate ion is exactly analogous to that in carbonate B 1. 17 There are four B-H bonds in BH4 The four electron pairs surround boron in a tetrahedral orien- tation.TheH—B— H angles are 109.5° 1. 18 (b) Nitrogen in ammonium ion is surrounded by 8 electron bonds are directed toward the corners of a tetrahedron s in four covalent bonds These four H H (c) Double bonds are treated as a single unit when deducing the shape of a molecule using the VSEPR model. thus azide ion is linear The nnn angle is180° (d) Since the double bond in carbonate ion is treated as if it were a single unit, the three sets of electrons are arranged in a trigonal planar arrangement around carbon. The OCO angle is 120. 1. 19 (b) Water is a bent molecule, and so the individual o-H bond dipole moments do not cancel. Water has a dipole moment Individual oh bond Direction of net (c) Methane, CHa, is perfectly tetrahedral, and so the individual(small)C-H bond dipole (d) Methyl chloride has a dipole moment H Directions of bond dipole Direction of molecular dipole moment Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
CHEMICAL BONDING 7 (d) Resonance in borate ion is exactly analogous to that in carbonate. and 1.17 There are four B@H bonds in BH4 . The four electron pairs surround boron in a tetrahedral orientation. The H@B@H angles are 109.5°. 1.18 (b) Nitrogen in ammonium ion is surrounded by 8 electrons in four covalent bonds. These four bonds are directed toward the corners of a tetrahedron. (c) Double bonds are treated as a single unit when deducing the shape of a molecule using the VSEPR model. Thus azide ion is linear. (d) Since the double bond in carbonate ion is treated as if it were a single unit, the three sets of electrons are arranged in a trigonal planar arrangement around carbon. 1.19 (b) Water is a bent molecule, and so the individual O@H bond dipole moments do not cancel. Water has a dipole moment. (c) Methane, CH4, is perfectly tetrahedral, and so the individual (small) C@H bond dipole moments cancel. Methane has no dipole moment. (d) Methyl chloride has a dipole moment. C Cl H H C Cl H H Directions of bond dipole moments in CH3Cl Direction of molecular dipole moment H H O H H O H H Individual OH bond moments in water Direction of net dipole moment C O O O The OCO angle is 120º. N N N The NNN angle is 180°. Each HNH angle is 109.5º. N H H H H O O O B B O O O O O O B B O O O Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
8 CHEMICAL BONDING (e) Oxygen is more electronegative than carbon and attracts electrons from it. Formaldehyde has H f nd dipole Direction of molecular maldehyde dipole moment (f) Nitrogen is more electronegative than carbon Hydrogen cyanide has a dipole moment Direction of bond dipole 1.20 The orbital diagram for sp-hybridized nitrogen is the same as for sp-hybridized carbon, except nitrogen has one more electron 2++ 2y++千 Ground electroni sp hybrid state of nitrogen state of nitrogen The unshared electron pair in ammonia(: NH, )occupies an sp-hybridized orbital of nitrogen. Each N-H bond corresponds to overlap of a half-filled sp hybrid orbital of nitrogen and a ls orbital of h 1.21 Silicon lies below carbon in the periodic table, and it is reasonable to assume that both carbon and silicon are sp-hybridized in H3CSiHy The C-Si bond and all of the C-H and Si-H bonds are o bonds C(2sp)-Si(sp )o bond C(2sp)-H(ls)o bond H- H-C-Si-H Si(3sp)-H(Is)o bond The principal quantum number of the carbon orbitals that are hybridized is 2; the principal quantum number for the silicon orbitals is 3 1. 22 (b) Carbon in formaldehyde(h,c=O)is directly bonded to three other atoms(two hydrogens and one oxygen). It is sp--hybridized (c) Ketene has two carbons in different hybridization states. One is sp-hybridized; the other is sp-hybridized. HC=C=O Bonded to Bonded to three atoms. wo atoms:罗p Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
(e) Oxygen is more electronegative than carbon and attracts electrons from it. Formaldehyde has a dipole moment. ( f ) Nitrogen is more electronegative than carbon. Hydrogen cyanide has a dipole moment. 1.20 The orbital diagram for sp3 -hybridized nitrogen is the same as for sp3 -hybridized carbon, except nitrogen has one more electron. The unshared electron pair in ammonia (• •NH3) occupies an sp3 -hybridized orbital of nitrogen. Each N@H bond corresponds to overlap of a half-filled sp3 hybrid orbital of nitrogen and a 1s orbital of hydrogen. 1.21 Silicon lies below carbon in the periodic table, and it is reasonable to assume that both carbon and silicon are sp3 -hybridized in H3CSiH3. The C@Si bond and all of the C@H and Si@H bonds are bonds. The principal quantum number of the carbon orbitals that are hybridized is 2; the principal quantum number for the silicon orbitals is 3. 1.22 (b) Carbon in formaldehyde (H2C?O) is directly bonded to three other atoms (two hydrogens and one oxygen). It is sp2 -hybridized. (c) Ketene has two carbons in different hybridization states. One is sp2 -hybridized; the other is sp-hybridized. H2C C O Bonded to three atoms: sp2 Bonded to two atoms: sp C H H H H H Si H Si(3sp3 C(2sp ) bond 3 ) C(2sp H(1s) bond 3 ) Si(3sp3 ) H(1s) bond Ground electronic state of nitrogen sp3 hybrid state of nitrogen (a) (b) Energy 2s 2p 2sp3 H C N Direction of bond dipole moments in HCN H C N Direction of molecular dipole moment Direction of bond dipole moments in formaldehyde Direction of molecular dipole moment C O H H C O H H 8 CHEMICAL BONDING Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website