Understanding Covalent Compounds: Properties, Bonds & Structures

1. Unit 4: Chapter 9 Covalent Compounds and Bonding

2. Properties of Covalent Compounds • A bond between nonmetals • Low melting and boiling points • Soft and “squishy” compared to ionic compounds • Don’t conduct in water • Not very soluble in water • (opposite of ionic compounds)

3. Lewis Dot diagrams

4. Covalent bonds • Nonmetals hold onto their valence electrons because they are very electronegative • Still want noble gas configuration. • Get it by sharing valence electrons with each other. • By sharing, both atoms get to count the electrons toward noble gas configuration.

5. F Covalent bonding • Fluorine has seven valence electrons

6. F F Covalent bonding • Fluorine has seven valence electrons • A second atom also has seven

7. F F Covalent bonding • Fluorine has seven valence electrons • A second atom also has seven • By sharing electrons

8. F F Covalent bonding • Fluorine has seven valence electrons • A second atom also has seven • By sharing electrons

9. F F Covalent bonding • Fluorine has seven valence electrons • A second atom also has seven • By sharing electrons

10. F F Covalent bonding • Fluorine has seven valence electrons • A second atom also has seven • By sharing electrons • Both end with full orbitals

11. Covalent bonding • Fluorine has seven valence electrons • A second atom also has seven • By sharing electrons • Both end with full orbitals F F 8 Valence electrons

12. Covalent bonding • Fluorine has seven valence electrons • A second atom also has seven • By sharing electrons • Both end with full orbitals F F 8 Valence electrons

13. How to show how they formed • It’s like a jigsaw puzzle. • You put the pieces together to end up with the right formula. • For example- show how water is formed with covalent bonds. • Tips: • Elements that need the most electrons will be the center atom • Bond each element to the center atom first

14. H O Water 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 happy

15. O Water • Put the pieces together • The first hydrogen is happy • The oxygen still wants one more H

16. O Water • The second hydrogen attaches • Every atom has full energy levels H H

17. Example • Lets try: • NH3 • CCl4

18. Multiple Bonds • Sometimes atoms share more than one pair of valence 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.

19. Bond Strength • Bond Disassociation Energy • amount of energy needed to break a bond • Triple> Double> Single • Think of seatbelts on a Roller Coaster • the more seat belts, the safer you are, less likely you are to fall out • The more “bonds”, harder to break

20. O Carbon dioxide • CO2- Carbon is central atom( I have to tell you) • Carbon has 4 valence electrons • Wants 4 more • Oxygen has 6 valence electrons • Wants 2 more C

21. O Carbon dioxide • Attaching 1 oxygen leaves the oxygen 1 short and the carbon 3 short C

22. O O Carbon dioxide • Attaching the second oxygen leaves both oxygen 1 short and the carbon 2 short C

23. O O Carbon dioxide • The only solution is to share more C

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

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

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

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

28. Carbon dioxide • The only solution is to share more O C O

29. Carbon dioxide • The only solution is to share more • Requires two double bonds • Each atom gets to count all the atoms in the bond O C O

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

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

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

33. Steps for Drawing Molecules • Draw Lewis Dot Structures of each element. • Form single bonds first between central element and “outside” elements • Add additional bonds so each element has a stable octet • Examples: • HCN

34. Another way of indicating bonds • Often use a line to indicate a bond • Called a structural formula • Each line is 2 valence electrons H O H H O H

35. Structural Examples • C has 8 electrons because each line is 2 electrons • Ditto for N • Same for C here • Same for O H C N H C O H

36. VSEPR • Valence Shell Electron Pair Repulsion. • Predicts three dimensional geometry of molecules. • Name tells you the theory. • Valence shell - outside electrons. • Electron Pair repulsion - electron pairs try to get as far away as possible. • Can determine the angles of bonds.

37. VSEPR • Based on the number of pairs of valence electrons both bonded and unbonded. • Unbonded pair are called lone pair. • CH4 - draw the structural formula

38. VSEPR • Single bonds fill all atoms. • There are 4 pairs of electrons pushing away. • The furthest they can get away is 109.5º. H H C H H

39. 4 atoms bonded • Basic shape is tetrahedral. • A pyramid with a triangular base. • Same shape for everything with 4 pairs. H 109.5º C H H H

40. 3 bonded - 1 lone pair • Still basic tetrahedral but you can’t see the electron pair. • Shape is called trigonal pyramidal. N H N H H H <109.5º H H

41. 2 bonded - 2 lone pair • Still basic tetrahedral but you can’t see the 2 lone pair. • Shape is called bent. O H O H <109.5º H H

42. 3 atoms no lone pair • The bonds are as far apart as possible • 120º H C O H

43. H O 3 atoms no lone pair • The bonds are as far apart as possible • 120º • Shape is flat and called trigonal planar. H 120º H C C O H

44. 2 atoms no lone pair • With three atoms the farthest they can get apart is 180º. • Shape called linear. 180º C O O

45. Covalent Compounds Writing names and Formulas

46. Covalent Compounds • made of just nonmetals • smallest piece is a molecule • can’t use charges to figure out how many of each atom

47. Easier • Ionic compounds use charges to determine how many of each. • Have to figure out charges. • Have to figure out subscripts. • Covalent compounds name tells you the number of atoms. • Uses prefixes to tell you the number

48. Prefixes • 1 mono- • 2 di- • 3 tri- • 4 tetra- • 5 penta- • 6 hexa- • 7 hepta- • 8 octa-

49. Prefixes • 9 nona- • 10 deca- • To write the name write two words First Element Second element Prefix name Prefix name -ide • One exception is we don’t write mono- if there is only one of the first element. • No double vowels when writing names (oa oo)

50. Write the Formula for These • N2O • NO2 • Cl2O7 • CBr4 • CO2 • Dinitrogen monoxide • Nitrogen dioxide • Dichlorine heptoxide • Carbon tetrabromide • Carbon dioxide