1. 1 CHEMICAL BONDING Cocaine Adapted from www.chemistrygeek.com

2. 2 Types of Chemical Bonds There are 3 forms of bonding:There are 3 forms of bonding: Ionic—complete transfer of 1 or more electrons from one atom to anotherIonic—complete transfer of 1 or more electrons from one atom to another Covalent—some valence electrons shared between atomsCovalent—some valence electrons shared between atoms Metallic – holds atoms of a metal togetherMetallic – holds atoms of a metal together

3. 3 Properties of Chemical Bonds PropertyIonicCovalentMetallic Nature of BondTransfer of ElectronsSharing of ElectronsFixed Cations surrounded by free- moving electrons Types of ElementsMetal and NonmetalNonmetalsMetals StateSolid CrystallineSolid, Liquid, GasSolid Melting/Boiling PointHighLowHigh ConductivityOnly when melted or dissolved NoneYes SolubilityGenerallyPolar – yes Nonpolar - no No

4. 4 The type of bond can usually be calculated by finding the difference in electronegativity of the two atoms that are going together.

5. 5 Electronegativity Difference If the difference in electronegativities is between: – 1.7 to 4.0: Ionic – 0.3 to 1.7: Polar Covalent – 0.0 to 0.3: Non-Polar Covalent Example: NaCl Na = 0.8, Cl = 3.0 Difference is 2.2, so this is an ionic bond!

6. 6 Valence Electrons Valence electrons are the electrons in the OUTERMOST energy levelValence electrons are the electrons in the OUTERMOST energy level Example 1: Boron (B) 1s 2 2s 2 2p 1Example 1: Boron (B) 1s 2 2s 2 2p 1 –Valence Level is 2 –3 Valence electrons Example 2: Bromine (Br) [Ar] 4s 2 3d 10 4p 5Example 2: Bromine (Br) [Ar] 4s 2 3d 10 4p 5 –Valence Level is 4 –7 Valence electrons

7. 7 Valence Electrons For Main Group Elements (A Groups) The Group Number = Valence ElectronsThe Group Number = Valence Electrons

8. 8 Electron Dot Structures Electron Dot Structures are diagrams that show Valence Electrons at dots Dots are filled in counterclockwise Fill one dot on all 4 sides before adding a second dot on a side NOTE: Helium has 2 dots, but it is not drawn like the elements in Group 2

9. 9 The Octet Rule Noble Gases have the most stable electron configurations because all orbitals are filled –Ne 1s 2 2s 2 2p 6 –Ar 1s 2 2s 2 2p 6 3s 2 3p 6 –Kr 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 The general Valence Configuration for a Noble Gas is ns 2 np 6, which has 8 Valence Electrons In forming compounds, atoms tend to lose, gain or share electrons in order to get 8 electrons in their Valence Electrons This is called the Octet Rule

10. 10 Ionic Bonds Metals and Nonmetals form Ionic Compounds to satisfy the octet rule on their atoms.Metals and Nonmetals form Ionic Compounds to satisfy the octet rule on their atoms. Cations lose electrons (form + charge)Cations lose electrons (form + charge) Na1s 2 2s 2 2p 6 3s 1 loses 1 electron from 3s to form Na + 1s 2 2s 2 2p 6 which now has a complete octet Anions gain electrons (form – charge)Anions gain electrons (form – charge) Cl 1s 2 2s 2 2p 6 3s 2 3p 5 gains 1 electron to 3p 5 to form Cl - 1s 2 2s 2 2p 6 3s 2 3p 6 which now has a complete octet Sodium will actually transfer it’s electron to Chlorine to form NaClSodium will actually transfer it’s electron to Chlorine to form NaCl

11. 11 Learning Check How many electrons will the following metals lose to form cations with filled octets? What is the charge on the ion? –Mg –Al –K –H How many electrons will the following nonmetals gain to form anions with filled octets? What is the charge on the ion? –F –O –N –S

12. 12 Ionic Bonds – Transfer Diagrams We can use electron dot structures to draw Transfer Diagrams to predict what ionic compound will form

13. 13 Learning Check Draw Transfer Diagrams for the following combination of Metals and Nonmetals and predict the ionic compound formed –K and I –Ca and Cl –Na and P –Al and O

14. 14 Covalent Bonding Nonmetals satisfy the Octet rule by sharing electrons to form Covalent Bonds Pairs of atoms can share 1, 2 or 3 pairs of electrons. –Single Bond – 1 pair of electrons is shared –Double Bond – 2 pairs of electrons is shared –Triple Bond – 3 pairs of electrons is shared Two categories of Covalent Bonds exist –Non-polar – equal sharing of electrons –Polar – unequal sharing of electron We can use diagrams called Lewis Structures to predict covalent bonding in molecules

15. 15 Lewis Structures Shared (Bond) Pair – electrons that are shared between 2 atomsShared (Bond) Pair – electrons that are shared between 2 atoms Unshared (Lone) Pair – electrons that only belong to one atomUnshared (Lone) Pair – electrons that only belong to one atom HCl lone pair (LP) shared or bond pair This is called a LEWIS structure.

16. 16 Bond Formation A bond can result from an overlap of atomic orbitals on neighboring atoms. Cl HH + Overlap of H (1s) and Cl (2p) Note that each atom has a single, unpaired electron.

17. 17 Steps for Building a Dot Structure Ammonia, NH 3 1.Decide on the central atom - Center atom can never be Hydrogen and rarely a Halogen (F, Cl, Br, I) - Center atom can never be Hydrogen and rarely a Halogen (F, Cl, Br, I) -If there is a choice, the central atom will have the lower electronegativity value -N will be the central atom for Ammonia 2. Add up the number of valence electrons that can be used. H = 1 and N = 5 H = 1 and N = 5 Total = (3 x 1) + 5 Total = (3 x 1) + 5 = 8 electrons / 4 pairs = 8 electrons / 4 pairs

18. 18 3.Form a single bond between the central atom and each surrounding atom (each bond takes 2 electrons!) H H H N Building a Dot Structure H H H N 4.Remaining electrons form LONE PAIRS to complete the octet as needed (or duet in the case of H). 3 BOND PAIRS and 1 LONE PAIR. Note that N has a share in 4 pairs (8 electrons), while each H shares 1 pair.

19. 19 5.Check to make sure there are 8 electrons around each atom except H. H should only have 2 electrons. This includes SHARED pairs. Building a Dot Structure 6. Also, check the number of electrons in your drawing with the number of electrons from step 2. If you have more electrons in the drawing than in step 2, you must make double or triple bonds. If you have less electrons in the drawing than in step 2, you made a mistake! H H H N

20. 20 Carbon Dioxide, CO 2 1. Central atom = 2. Valence electrons = 3. Form bonds. 4. Place lone pairs on outer atoms. This leaves 12 electrons (6 pair). 5. Check to see that all atoms have 8 electrons around it except for H, which can have 2. C 4 e- O 6 e- X 2 O’s = 12 e- Total: 16 valence electrons

21. 21 Carbon Dioxide, CO 2 6. There are too many electrons in our drawing. We must form DOUBLE BONDS between C and O. Instead of sharing only 1 pair, a double bond shares 2 pairs. So one pair is taken away from each atom and replaced with another bond. C 4 e- O 6 e- X 2 O’s = 12 e- Total: 16 valence electrons How many are in the drawing?

22. 22 Double and Triple bonds are commonly observed for C, N, P, O, and S H 2 CO SO 3 C2F4C2F4C2F4C2F4

23. 23 Learning Check Draw Lewis Structures for the following compounds H 2 O CH 4 PCl 3 O 2 N 3

24. 24 Polyatomic Ions and Covalent Bonds (WH) Anions – add the electrons gained from the charge to the valence (step 2) Cations – subtract the electrons lost from the charge to the valence (step 2) Put [ ] around the entire structure, and indicate the charge at the top right

25. 25 Violations of the Octet Rule (Honors only) Usually occurs with Be, B, P, S and Xe and elements of higher periods. These elements can have the following numbers of valence e - BF 3 SF 4 Be: 4 B: 6 P: 8 OR 10 S: 8, 10, OR 12 Xe: 8, 10, OR 12

26. 26 Learning Check (WH) Draw the following Lewis Structures for the Exceptions to the Octet Rule –BF 3 –PCl 5 –SF 6 –BeF 2

27. 27 MOLECULAR GEOMETRY

28. 28 VSEPR VSEPR V alence S hell E lectron P air R epulsion theory.V alence S hell E lectron P air R epulsion theory. Most important factor in determining geometry is relative repulsion between electron pairs.Most important factor in determining geometry is relative repulsion between electron pairs. Molecule adopts the shape that minimizes the electron pair repulsions. MOLECULAR GEOMETRY

29. 29 Some Common Geometries Linear Trigonal Planar Tetrahedral

30. 30 VSEPR charts Use the Lewis structure to determine the geometry of the moleculeUse the Lewis structure to determine the geometry of the molecule Electron arrangement establishes the bond anglesElectron arrangement establishes the bond angles Molecule takes the shape of that portion of the electron arrangementMolecule takes the shape of that portion of the electron arrangement Charts look at the CENTRAL atom for all data!Charts look at the CENTRAL atom for all data! Think REGIONS OF ELECTRON DENSITY rather than bonds (for instance, a double bond would only be 1 region)Think REGIONS OF ELECTRON DENSITY rather than bonds (for instance, a double bond would only be 1 region)

31. 31 Other VSEPR charts

32. 32 Structure Determination by VSEPR Water, H 2 O The electron pair geometry is TETRAHEDRAL The molecular geometry is BENT. 2 bond pairs 2 lone pairs

33. 33 Structure Determination by VSEPR Ammonia, NH 3 The electron pair geometry is tetrahedral. The MOLECULAR GEOMETRY — the positions of the atoms — is TRIGONAL PYRAMID.

34. 34 Learning Check Identify the Molecular Geometry of the following molecules –H 2 S –PH 3 – CH 4 –CO 2 –C 2 H 6

35. 35 Bond Polarity Not all electrons are always shared equally in a covalent bond Nonpolar Covalent Bond – electrons are shared equally between 2 atoms –Usually occurs between 2 atoms of the same element or similar electronegativity –Difference in electronegativity between 0.0 to 0.3 Polar Covalent Bond – electrons are shared unequally between 2 atoms –Occurs between 2 atoms that have different electronegativities –Difference in electronegativity between 0.3 to 1.7

36. 36 Polar Molecules A molecule is Polar when it has a positive end and a negative end (a Dipole) due to large difference in electronegativity (0.9 for HCl) The element with the larger electronegativity will have a slightly negative charge, the other element will become slightly positive Cl has slight negative charge (-  ) and H has slight positive charge (+  )

37. 37 Non Polar Molecules There are 2 ways a molecule can be nonpolar 1.The atoms in the molecule have a very low difference in electronegativity (no Dipole) -The 2 Cl atoms have equal electronegativity values, so no dipole occurs 2. The bonds in the molecule are polar but the dipoles cancel out. This usually occurs in a symmetrical molecule. –CO 2 contains 2 polar bonds but because they are equal and opposite to each other, they cancel out. CO 2 is a nonpolar molecule

38. 38 Polar molecules can only mix with other polar moleculesPolar molecules can only mix with other polar molecules Nonpolar molecules can only mix with other nonpolar moleculeNonpolar molecules can only mix with other nonpolar molecule The general rule for mixing substances is “Like Dissolves Like”The general rule for mixing substances is “Like Dissolves Like” Bond Polarity

39. 39 Bond Polarity This is why oil and water will not mix! Oil is nonpolar, and water is polar.This is why oil and water will not mix! Oil is nonpolar, and water is polar. The two will repel each other, and so you can not dissolve one in the otherThe two will repel each other, and so you can not dissolve one in the other

40. 40 Learning Check Draw Lewis Structures and predict the polarity of the following molecules –H 2 –N 2 –CH 4 –H 2 O –HF –C 2 H 6

41. 41 Intermolecular Forces Intermolecular Force – attraction between molecules –Typically weaker than ionic or covalent bonds –Determine Physical Properties of Substance (state of matter, density, boiling/melting points, etc) Van der Waals Forces –Dipole Interactions –Dispersion Forces Hydrogen Bonding

42. 42 Van der Waals Forces Dispersion Forces – occurs due to random movements of electrons –Weakest IMF –Occurs in polar and nonpolar molecules –Causes brief dipole moments, which creates slight attraction between molecules Dipole Interactions –Occurs when slightly negative regions are attracted to slightly positive regions of polar molecules

43. 43 Hydrogen Bonding Hydrogen bonding – occurs when hydrogen is covalently bonded to a highly electronegative element (like O, N, F) –H is electron deficient –High attraction to negative regions of adjacent molecules Occurs in Water –H-bonding creates water’s unique properties (low density solid, cohesion, adhesion, surface tension, etc)

44. 44 Network Solid Network Solid – solid in which all atoms are covalently bonded to each other –Often form a crystal-like structure –Very high melting points and stable structure –Only common with elements like C and Si because they can form 4 covalent bonds –Diamond is a network solid