Lewis Dot Structure, polarity, molecule shapes, forces Covalent Compounds  Lewis Dot Structure, polarity, molecule shapes, forces

Electronegativity Scale Boundary   1.7-1.9 *look at what is making the bond* Non-polar covalent Polar covalent Ionic O O.4 1.7 1.9 3

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

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

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

Preferred bonding H C N O

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

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

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

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

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

How to predict shapes Draw LSD for the compound Count the number of unpaired and bonded pairs around the CENTRAL ATOM Predict shape

Types of Shape Open page 14 and 15 in the bonding packet for full list

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

Is it polar? Polar: not symmetrical Polar: Unbonded pairs Non-Polar: poles are the same Non-Polar: symmetrical

Intermolecular Forces Van Der Walls, London Dispersion, Induced Dipoles Dipole-Dipole Hydrogen Bonding

Van Der Walls, London Dispersion, Induced Dipole Random movement of electron creates a temporary negative and positive pole All electrons are on one side

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)

Hydrogen Bonding NOT REAL BONDING: type of dipole-dipole ONLY when H is bonded to N,F, or O

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