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Lewis Dot Structure, polarity, molecule shapes, forces
Covalent Compounds Lewis Dot Structure, polarity, molecule shapes, forces
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Electronegativity Scale
Boundary *look at what is making the bond* Non-polar covalent Polar covalent Ionic O O.4 1.7 1.9 3
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Lewis Dot Structure –Single elements
Steps to draw Determine valence electrons Write the Chemical symbol Place the electrons around the outside of symbol Dots are used as electrons
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Lets Draw some element Lewis Dot Structures!
Chlorine Cl: 7 Valence (group 17) Cl Sodium Na: 1 Valence (group 1) Na Carbon C: 4 valence (group 14) C
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Lewis Dot Structures for compounds
A representation of where the electrons are shared in covalent compounds A line shows a bonding pair of electrons One line = 2 electrons A dot show unbonded electrons
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Preferred bonding H C N O
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Steps to make LDS for compounds
Determine valence electrons for all elements Add all the valence electrons together Total for the compound (MAX #) Determine placement of elements Most electro-positive element in center NEVER Hydrogen Place bonds to connect , start with single bonds first Place remaining electrons OR create multiple bond if NEEDED Multiple bonds are needed ONLY when octet cannot be achieved Check for octet
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Example H O H H O H H2O H: 2(1 valence) O: 6 valence Total: 8 valence
Step 3: Draw Structure/ Place bonds and electrons Step 1:Calculate valence H2O H: 2(1 valence) O: 6 valence Total: 8 valence 8 valence -4 (2 bonds) 4 valence left -4 (lone electrons) 0 valence left! Step 4: Check for octet/duet rule Step 2: Place elements H O H H O H
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LDS with Multiple bonds
Step 3: Draw Structure 16 valence 4 electrons 12 e- left Step 1: Calculate Valence CO2 C: 4 valence O: 2 x 6 valence Total valence: 16 Can you even distribute remaining electrons AND have each element obey octet rule? NO! Time for multiple bonds 12 valence 12 electrons 8 in unbonded pairs 4 in double bonds Step 2: Which element is the most electro POSITIVE O C O O C O
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Resonance Structure When multiple valid structures can be drawn for the SAME compound Multiple electrons can move around within bonds (delocalize) The real structure is hybrid of all the resonance structures
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VSEPR Theory A way to predict the shape and properties of covalent compounds Bonded and unbonded (unpaired) electrons V: Valence S: Shell E: Electron P:Pair R:Repullsion
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How to predict shapes Draw LSD for the compound
Count the number of unpaired and bonded pairs around the CENTRAL ATOM Predict shape
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Types of Shape Open page 14 and 15 in the bonding packet for full list
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Polarity Electronegativity difference within a molecule
No difference/slight difference/symmetrical molecule: Non- polar Large difference/ non-symmetrical molecule: Polar Dipole: two poles with difference partial charges
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Is it polar? Polar: not symmetrical Polar: Unbonded pairs
Non-Polar: poles are the same Non-Polar: symmetrical
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Intermolecular Forces
Van Der Walls, London Dispersion, Induced Dipoles Dipole-Dipole Hydrogen Bonding
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Van Der Walls, London Dispersion, Induced Dipole
Random movement of electron creates a temporary negative and positive pole All electrons are on one side
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Dipole-Dipole When there is an Electronegativity difference
One side has a partial negative (bonding pair closer to the high EN) One side has partial positive (bonding pair further away from the low EN)
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Hydrogen Bonding NOT REAL BONDING: type of dipole-dipole
ONLY when H is bonded to N,F, or O
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What force goes with what?
Polar Molecules Non-polar molecules Dipole-dipole Hydrogen bonding ONLY when H is bonded to N,F, or O London Dispersion London Dispersion
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