ch10-s-1 - 10 1 Chapter 10 The Shapes of Molecules 10.1...

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Unformatted text preview: 10 - 1 Chapter 10: The Shapes of Molecules 10.1 Depicting Molecules and Ions with Lewis Structures 10.2 Valence-Shell Electron-Pair Repulsion (VSEPR) Theory and Molecular Shape 10.3 Molecular Shape and Molecular Polarity 10 - 2 Lewis Structures • 1) Only the valence electrons appear in a Lewis structure. • 2) The line joining two atoms represents a pair of electrons shared between two atoms. – single bond- two shared electrons, one line – double bond- four shared electrons, two lines – triple bond- six shared electrons, three lines • 3) Dots placed next to an atom represent nonbonding electrons. 10 - 3 Lewis Structures of the Elements by Group in the Periodic Table Group I II III IV V VI H Li Na . . . . Be Mg Ca . . . . . . . . B Al . . . . . . . . . . . . . C Si . . . . . . . . . . N P . . . . . . O . . . . . . S VII VIII F Cl . . . . . . . . . . . . . . . . . . He Ne Ar . . . . . . . . . . . . 10 - 4 Fig. 10.1 10 - 5 Writing Lewis Structures - I Step 1) Place the atoms relative to each other. For compounds of formula AB n , place the atom with the lower group number in the center, the one that needs more electrons to attain an octet. In NF 3 (nitrogen trifluoride), the N (Group 15) has five electrons so it needs three, whereas F (Group 17) has seven so it needs only one; thus, N goes in the center with the three F atoms around it. Step 2) Determine the total number of valence electrons available. For molecules, add up the valence electrons of all atoms (the number of valence electrons equals the group number). In NF 3 , N has five valence electrons, and each F has seven. For polyatomic ions, add 1 e- for for each negative charge, or subtract 1 e- for each positive charge. 10 - 6 Writing Lewis Structures - II Step 3) Draw a single bond from each surrounding atom to the central atom, and subtract two valence electrons for each bond. There must be at least a single bond between bonded atoms. Step 4) Distribute the remaining electrons in pairs so that each atom obtains eight electrons (or two for H). Place lone pairs on the surrounding (more electronegative) atoms first to give each an octet. If electrons remain, place them around the central atom. Then check that each atom has 8 e- . 10 - 7 Lewis Structures of Simple Molecules - I H H H H H H . . . . . . . . . . . . H H F F . . . . . . . . . . . . . . . . H Cl Sodium Chloride Na + Cl . . . . . .- Molecular Fluorine Hydrogen Chloride Molecular Hydrogen Magnesium Chloride Mg +2 Cl Cl . . . . . . . . . . . . . .- . .- C C H H H H H H . . . . . . . . . . . . . . Ethane F F . . . . . . . . . . . . . . H F . . . . Hydrogen Fluoride 10 - 8 Lewis Structures of Simple Molecules - II CH 4 Methane C H H H H H C C H H H H O O C 2 H 4 O 2 Acetic Acid C Cl Cl Cl Cl .....
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ch10-s-1 - 10 1 Chapter 10 The Shapes of Molecules 10.1...

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