More on Covalent Bonding

Lewis dot structures of covalent molecules.

H H C H H Two ways of writing Lewis Structures

H Lone pairs:

H + H N H H ammonia ammonium

Lewis diagrams are only two dimensional and are not intended to show a 3-D view of a molecule or ion.

DDT Cl Cl C Cl C

Drawing Lewis Formulae The Rules In most covalent compounds, representative elements follow the octet rule EXCEPT H – which always shares TWO e-In most covalent compounds, representative elements follow the octet rule EXCEPT H – which always shares TWO e- H forms only one bond to another element; thus H can never be a central atomH forms only one bond to another element; thus H can never be a central atom

Drawing Lewis Formulae Carbon ALWAYS forms 4 bonds.Carbon ALWAYS forms 4 bonds. This can be accomplished byThis can be accomplished by Four single bonds Four single bonds Two double bondsTwo double bonds Two single bonds and a double bondTwo single bonds and a double bond One single bond and one triple bondOne single bond and one triple bond In neutral, uncharged species N forms three bonds, O forms twoIn neutral, uncharged species N forms three bonds, O forms two

Drawing Lewis Formulae Nonmetals can form single, double or triple bonds but never quadruple bondsNonmetals can form single, double or triple bonds but never quadruple bonds Carbon forms double or triple bonds to C, N, O or S. O can form double bonds with many other elementsCarbon forms double or triple bonds to C, N, O or S. O can form double bonds with many other elements

Covalent bonds Nonmetals hold onto their valence electrons.Nonmetals hold onto their valence electrons. Still want noble gas configuration.Still want noble gas configuration. Get it by sharing valence electrons with each other.Get it by sharing valence electrons with each other. Both atoms get to count the electrons toward noble gas configuration.Both atoms get to count the electrons toward noble gas configuration.

Covalent Bonding sharing of electrons

Repulsions keep atom from collapsing

Movement of electrons in covalent bond

Core electrons not involved in bonding

Sharing of valence electrons to obtain stable octets

Single Covalent Bond A sharing of two valence electrons.A sharing of two valence electrons. Different from an ionic bond because they actually form molecules.Different from an ionic bond because they actually form molecules.

Water H O Each hydrogen has 1 valence electron Each hydrogen wants 1 more The oxygen has 6 valence electrons The oxygen wants 2 more

Water Hydrogen can share one electron with the oxygenHydrogen can share one electron with the oxygen However, the oxygen still wants one moreHowever, the oxygen still wants one more H O

Water The second hydrogen attachesThe second hydrogen attaches Every atom has full energy levelsEvery atom has full energy levels H O H

Multiple Bonds Sometimes atoms share more than one pair of valence electrons.Sometimes atoms share more than one pair of valence electrons. A double bond is when atoms share two pair (4) of electrons.A double bond is when atoms share two pair (4) of electrons. A triple bond is when atoms share three pair (6) of electrons.A triple bond is when atoms share three pair (6) of electrons.

Carbon dioxide CO 2 - Carbon is central atomCO 2 - Carbon is central atom Carbon has 4 valence electronsCarbon has 4 valence electrons Wants 4 moreWants 4 more Oxygen has 6 valence electronsOxygen has 6 valence electrons Wants 2 moreWants 2 more O C

Carbon dioxide Attaching 1 oxygen leaves the oxygen 1 short and the carbon 3 shortAttaching 1 oxygen leaves the oxygen 1 short and the carbon 3 short O C

Carbon dioxide l Attaching the second oxygen leaves both oxygen 1 short and the carbon 2 short O C O

Carbon dioxide l The only solution is to share more O C O

Carbon dioxide O C O l The only solution is to share more

Carbon dioxide O CO l The only solution is to share more

Carbon dioxide O CO l The only solution is to share more

Carbon dioxide O CO l The only solution is to share more

Carbon dioxide O CO l The only solution is to share more

Carbon dioxide l The only solution is to share more l Requires two double bonds l Each atom gets to count all the atoms in the bond O CO

Carbon dioxide l The only solution is to share more l Requires two double bonds l Each atom gets to count all the atoms in the bond O CO 8 valence electrons

Carbon dioxide l The only solution is to share more l Requires two double bonds l Each atom gets to count all the atoms in the bond O CO 8 valence electrons

Carbon dioxide l The only solution is to share more l Requires two double bonds l Each atom gets to count all the atoms in the bond O CO 8 valence electrons

How to draw them Add up all the valence electrons.Add up all the valence electrons. Count up the total number of electrons needed by each atom (i.e. 8 x the number of atoms, remember only 2 for H)Count up the total number of electrons needed by each atom (i.e. 8 x the number of atoms, remember only 2 for H) Subtract.Subtract. Divide by 2Divide by 2 Tells you how many bonds - draw them.Tells you how many bonds - draw them. Fill in the rest of the valence electrons to fill atoms up.Fill in the rest of the valence electrons to fill atoms up.

Examples NH 3NH 3 N - has 5 valence electrons wants 8N - has 5 valence electrons wants 8 H - has 1 valence electrons wants 2H - has 1 valence electrons wants 2 Valence electrons = 8Valence electrons = 8 NH 3 wants 8+3(2) = 14NH 3 wants 8+3(2) = 14 (14-8)/2= 3 bonds(14-8)/2= 3 bonds 4 atoms with 3 bonds4 atoms with 3 bonds N H

NHH H Examples Draw in the bondsDraw in the bonds All 8 electrons are accounted forAll 8 electrons are accounted for Everything is fullEverything is full

Examples HCN C is central atomHCN C is central atom N - has 5 valence electrons wants 8N - has 5 valence electrons wants 8 C - has 4 valence electrons wants 8C - has 4 valence electrons wants 8 H - has 1 valence electrons wants 2H - has 1 valence electrons wants 2 HCN has = 10HCN has = 10 HCN wants = 18HCN wants = 18 (18-10)/2= 4 bonds(18-10)/2= 4 bonds 3 atoms with 4 bonds -will require multiple bonds - not to H3 atoms with 4 bonds -will require multiple bonds - not to H

HCN Put in single bondsPut in single bonds Need 2 more bondsNeed 2 more bonds Must go between C and NMust go between C and N NHC

HCN l Put in single bonds l Need 2 more bonds l Must go between C and N l Uses 8 electrons - 2 more to add NHC

HCN l Put in single bonds l Need 2 more bonds l Must go between C and N l Uses 8 electrons - 2 more to add l Must go on N to fill octet NHC

Another way of indicating bonds Often use a line to indicate a bondOften use a line to indicate a bond Called a structural formulaCalled a structural formula Each line is 2 valence electronsEach line is 2 valence electrons HHO = HHO

Structural Examples H CN C O H H C has 8 electrons because each line is 2 electronsC has 8 electrons because each line is 2 electrons Ditto for NDitto for N Ditto for C hereDitto for C here Ditto for ODitto for O

More on Covalent bonding

Coordinate Covalent Bond When one atom donates both electrons in a covalent bond.When one atom donates both electrons in a covalent bond. Carbon monoxideCarbon monoxide COCO OC

Coordinate Covalent Bond l When one atom donates both electrons in a covalent bond. l Carbon monoxide l CO OC

Coordinate Covalent Bond l When one atom donates both electrons in a covalent bond. l Carbon monoxide l CO OC

Draw the Lewis Dot Notation For these AND state whether they are ionic or covalentAND state whether they are ionic or covalent Carbon tetrachlorideCarbon tetrachloride Sodium bromideSodium bromide Sulfur trioxideSulfur trioxide

Resonance & Exceptions To be done on the boardTo be done on the board