Chy102-Tutorial 07

Chy102-Tutorial 07 - General Chemistry General Chem. 102...

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1 General Chemistry Chem. 102 for Engineering General Chemistry General Chemistry Tutorial 7
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2 Valence Electrons 1A 1A 2A 2A 3A 3A 4A 4A 5A 5A 6A 6A 7A 7A 8A 8A Number of valence electrons is equal to the Group number.
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3 Step 2. Count valence electrons S = 6 3 x O = 3 x 6 = 18 Negative charge = 2 TOTAL = 6 + 18 + 2 = 26 e- or 13 pairs Step 1. Central atom = S 10 pairs of electrons are left. Sulfite ion, SO 3 2- Step 3. Form sigma bonds OO O S
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4 Remaining pairs become lone pairs, first on outside atoms then on central atom. Sulfite ion, SO 3 2- (2) Each atom is surrounded by an octet of electrons. O O O S •• •• •• •• •• •• -1 -1 -1 +1 2-
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5 1) Chemical formula: 1) Chemical formula: 2) Atomic arrangement: 2) Atomic arrangement: H N O 3 Number of valence electrons = 24 Number of valence electrons = 24 3) Number of bonds 3) Number of bonds = 5 = 5 4) Remaining electrons 4) Remaining electrons = 14 = 14 5) Complete Lewis Structure 5) Complete Lewis Structure with with 14 14 remaining electrons remaining electrons H H N N O O O O O O H H N N O O O O O O H H N N O O O O O O Example: Write the Lewis structure for HNO 3 (two central atoms)
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6 Some additional structures and observations Isoelectronic molecules have the same number of valence electrons and thus the same Lewis Dot Structures NO + , N 2 , CO, CN - all have 10 electrons H 3 O + , NH 3: 8 valence electrons CO 2 , OCN - , SCN - , N 2 O, NO 2 + , COS, CS 2 : 16 valence electrons CO 3 2- , NO 3 - : 20 valence electrons PO 4 3- , SO 4 2- , ClO 4 - : 32 valence electrons [ NO ] + NN CO CN [ ] - NH H H O H H H + O N - C N S - + ONO OC S S C S O O - O O - N O O O - P O O O O 3- etc. S O O OO 2- etc.
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7 Lewis Structures: Examples a) CH a) CH 2 ClF ClF b) b) SO SO 2 c) SO c) SO 4 2- d) H d) H 3 PO PO 4 HC F Cl H OSO OS O O O H P O O O O H H S O O O O 2
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8 A resonance structure is one of two or more Lewis structures for a single molecule that cannot be represented accurately by only one Lewis structure.
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Chy102-Tutorial 07 - General Chemistry General Chem. 102...

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