Chapter6

Assign two bonding electrons as one shared pair to

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Unformatted text preview: the number in step 2. This Subtract is the number of shared (or bonding) electrons present (S). shared H C H H H C H H C H C H N−A = 12/04/09 Zumdahl Chapter 13 37 1. Assign two bonding electrons (as one shared pair) to each connection between two atoms in the molecule or ion. H C H C H H H 2 C 2C 2 2 H 2 H H 12/04/09 Zumdahl Chapter 13 38 1. If any of the electrons earmarked for sharing remain, assign If them in pairs by making some of the bonds double or triple bonds. In some cases, there may be more than one way to do bonds In this. Typically, double or triple bonds form only between atoms of carbon, nitrogen, oxygen, and sulfur. and H H 2 2 C 2 2 C 2 H H 12/04/09 Zumdahl Chapter 13 39 Lewis Structure of Carbon Monoxide (CO) Lewis 1. Count up the total number of valence electrons available (A) by 1. Count total available by first adding the group numbers of all the atoms present. If the species is a negative ion, add the absolute value of the total add charge; if it is a positive ion, subtract it. subtract · ·C· · · ·O: ·· 12/04/09 Zumdahl Chapter 13 40 1. Calculate the total number of electrons needed (N) for each atom Calculate total needed for to have its own noble-gas set of electrons around it (two for own hydrogen, eight for the elements from carbon on in the periodic table). table). 12/04/09 Zumdahl Chapter 13 41 1. Subtract the number in step 1 from the number in step 2. This is the number of shared (or bonding) electrons present (S). 12/04/09 Zumdahl Chapter 13 42 1. Assign two bonding electrons (as one shared pair) to each connection between two atoms in the molecule or ion. 2 C──O 12/04/09 Zumdahl Chapter 13 43 1. If any of the electrons earmarked for sharing remain, assign If them in pairs by making some of the bonds double or triple bonds. In some cases, there may be more than one way to do bonds In this. Typically, double or triple bonds form only between atoms of carbon, nitrogen, oxygen, and sulfur. carbon nitrogen oxygen and sulfur C 12/04/09 2 O Zumdahl Chapter 13 44 1. Assign the remaining electrons (A − S) as lone pairs to the atoms, giving octets to all atoms except hydrogen. (2 lone pairs) 2 C O C O O O 45 2 C C 12/04/09 Zumdahl Chapter 13 1. Determine the formal charge (C) on each atom, and write it next Determine on to that atom. Check that the formal charges add to give a correct total charge on the molecule or molecular ion. correct What is the formal charge on the carbon atom 4 in methane (CH )? in C ≡ group no. − no. of lone pair electrons − ½ (no. of electrons in bonding pairs) (no. 12/04/09 Zumdahl Chapter 13 46 What is the formal charge on each hydrogen atom in 4 methane (CH )? methane C ≡ group no. − no. of lone pair electrons − ½ (no. of electrons in bonding pairs) (no. As should be the case for the neutral molecule CH4, 12/04/09 Zumdahl Chapter 13 47 1. Determine the formal charge (C) on each atom, and write it Determine formal on next to that atom. Check that the formal charges add to give a...
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