1 Covalent bonding

2 How does H 2 form? l The nuclei repel ++

3 How does H 2 form? ++ l The nuclei repel l But they are attracted to electrons l The hydrogen atoms share the electrons

4 Covalent bonds l Nonmetals hold onto their valence electrons. l They can’t give away electrons to bond. –But the atoms still want noble gas configuration l Nonmetals get a noble gas configuration by sharing valence electrons with each other. –By sharing both atoms count the shared electrons toward noble gas configuration.

5 Covalent bonding l Fluorine has seven valence electrons 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 full orbitals 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 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 l Instead of dots, we use a “–” for the bond FF

16 Single Covalent Bond l The sharing of two valence electrons. –Only nonmetals and metalloids form covalent bonds Do not forget about Hydrogen! l Different from an ionic bond because they actually form molecules. –Ionic bonds are a matrix of ions –In an ionic solid you can’t tell which atom the electrons moved from or to.

17 How to show how they formed l I have to tell you what the final formula is or you cannot write the structure –Ionic compounds you can write the formula based on charges l You put the pieces together to end up with the right formula. l For example- show how water is formed with covalent bonds.

18 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 satisfy the octet

19 Water l Put the pieces together l The first hydrogen is good l The oxygen still wants one more electron H O

20 Water l The second hydrogen attaches l Every atom has full energy levels H O H

21 Water l The second hydrogen attaches l Every atom has full energy levels l Change the dots to lines HO H

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

23 Carbon dioxide l CO 2 - Carbon is central atom –Assume the first atom is central l Carbon has 4 valence electrons –Carbon wants 4 more l Oxygen has 6 valence electrons –Oxygen wants 2 more O C

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

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

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

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

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 O CO

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

32 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

33 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

34 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

35 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

36 How to draw them 1.Add up all the valence electrons. (to keep track) 2.Draw the central atom (or connect multiple central atoms by single bonds) 3.Connect the outer atoms to the central atom using a single bond 4.Complete the octet of the outer atoms 5.Place all extra electrons on the central atom(s) 6.Complete the octet of the central atom by making multiple bonds

37 Practice l NH 3 l H 2 O l HCN l H 2 CO l C 5 H 10 (multiple possible structures)

38 Structural Examples H CN C O H H

39 What about resonance? l Resonance is when you can create more than one structure that “appear” to be the same –Only the position of the number of bonds connecting atoms is switched. –But all the bonds must originate from the same central atom l Draw O 3

40 What about Exceptions to the Octet? l Sometimes a central atom will not complete an octet –Draw BF 3 l Sometimes the central atom will need to have more than an octet to satisfy the octet of the other atoms. –Draw XeF 4

41 What about ions? l When drawing a polyatomic ion, you will need to add or subtract the appropriate number of electrons. –Draw NH 4 + –Draw CO -2 –Draw OH -