1 “Covalent Bonding” Ball-and-stick model

2 Bonds are… Forces that hold groups of atoms together and make them function as a unit. Two types: 1) Ionic bonds – transfer of electrons (gained or lost; makes formula unit) 2) Covalent bonds – sharing of electrons. The resulting particle is called a “molecule”

3 Covalent Bonds l The word covalent is a combination of the prefix co- (from Latin com, meaning “with” or “ together ”), and the verb valere, meaning “to be strong ”. l Two electrons shared together have the strength to hold two atoms together in a bond.

4 Molecules  Many elements found in nature are in the form of molecules:  a neutral group of atoms joined together by covalent bonds.  For example, air contains oxygen molecules, consisting of two oxygen atoms joined covalently  Called a “diatomic molecule” (O 2 )

5 Covalent bonding l Fluorine has seven valence electrons (but would like to have 8) F

6 Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven FF

7 Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons… FF

8 Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons… FF

9 Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons… FF

10 Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons… FF

11 Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons… FF

12 Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons… l … both end with octet configuration FF

13 Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons… l …both end with full orbitals FF 8 Valence electrons

14 Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons… l …both end with full orbitals FF 8 Valence electrons

15 Molecular Compounds l Compounds that are bonded covalently (like in water, or carbon dioxide) are called molecular compounds

16 A Single Covalent Bond is... l A sharing of two valence electrons. l Only nonmetals and hydrogen. l Form molecules l Two atoms are joined together

17 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 They share to make each other complete

18 Water l Put the pieces together l The first hydrogen is happy l The oxygen still needs one more H O

19 Water l So, a second hydrogen attaches l Every atom has full energy levels H O H Note the two “unshared” pairs of electrons

20 Multiple Bonds l Sometimes atoms share more than one pair of valence electrons. l A double bond is when atoms share two pairs of electrons (4 total) l A triple bond is when atoms share three pairs of electrons (6 total) l These 7 elements as diatomic: Br 2 I 2 N 2 Cl 2 H 2 O 2 F 2

21 Dot diagram for Carbon dioxide l CO 2 - Carbon is central atom ( more metallic ) l Carbon has 4 valence electrons l Wants 4 more l Oxygen has 6 valence electrons l Wants 2 more O C

22 Carbon dioxide l Attaching 1 oxygen leaves the oxygen 1 short, and the carbon 3 short O C

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

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

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

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

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

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

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

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

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

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

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

34 Example l NH 3, which is ammonia l N – central atom; has 5 valence electrons, wants 8 l H - has 1 (x3) valence electrons l 4 atoms with 3 bonds N H

35 NHH H Examples l Draw in the bonds; start with singles l All 8 electrons are accounted for l Everything is full – done with this one.

36 Example: HCN l HCN: C is central atom l N - has 5 valence electrons, wants 8 l C - has 4 valence electrons, wants 8 l H - has 1 valence electron, wants 2 l 3 atoms with 4 bonds – this will require multiple bonds

37 HCN l Put single bond between each atom l Need to add 2 more bonds l Must go between C and N (Hydrogen is full) NHC

38 HCN l Put in single bonds l Needs 2 more bonds l Must go between C and N, not the H l Uses 8 electrons – need 2 more to equal the 10 it has NHC

39 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 the N to fill its octet NHC

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

41 Other Structural Examples H CN C O H H

42 A Coordinate Covalent Bond... l When one atom donates both electrons in a covalent bond. l Carbon monoxide (CO) is a good example: OC Both the carbon and oxygen give another single electron to share

43 Coordinate Covalent Bond l When one atom donates both electrons in a covalent bond. l Carbon monoxide (CO) is a good example: OC Oxygen gives both of these electrons, since it has no more singles to share. This carbon electron moves to make a pair with the other single.

44 Coordinate Covalent Bond l When one atom donates both electrons in a covalent bond. l Carbon monoxide (CO) OC C O The coordinate covalent bond is shown with an arrow as:

45 Covalent Network Compounds Some covalently bonded substances DO NOT form discrete molecules. Diamond, a network of covalently bonded carbon atoms Graphite, a network of covalently bonded carbon atoms

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