1. Covalent Bonds All atoms want an octet (Octet Rule) –Can share valence e-s e-s occupy molecular orbitals Where are e-s located? –Attraction and repulsion of e-s and p+s Molecule is more stable than atoms –Minimum energy (Ep) Can share 1, 2, or 3 pair e-s –Single, double, triple bond

2. Bond Properties Bond distance Bond energy Polarity

3. Bond Distance Distance between nuclei of bonded atoms –Distance at lowest Ep –single > double > triple –Smaller atoms bond closer together H – F H – Cl H – Br H – I (9.2) (12.7) (14.1) (16.1) relative bond dist

4. Bond Energy Energy needed to break mol of cov bonds –At minimum energy bal of attr and repulsion of e- and p+ of both atoms e- free to move about both nuclei = more stable – C C < C C < C C (347) (612) (820) units = kJ/mol –Smaller atom held together stronger H – F H – Cl H – Br H – I (565) (431) (360) (297) kJ/mol Inversely related

5. Polarity Unequal sharing of e-s –Due to diff in electronegativities F = 4.0 Fr = 0.8 –Dipole moment Measure of the strength of polarization Polar molecules have charged ends

6. Lewis Structures Show atoms and their arrangement in a molecule Octet rule –All atoms gain an octet (except H and He) Know rules pg 166 See powerpoint on Lewis Structures

7. Lewis Structures Bonding and nonbonding e- pairs Resonance –Formal charge Exceptions to the octet rule –Octet deficiencies –Expanded octets Molecular geometry –VSEPR theory Hybridization

8. Resonance 2 or more Lewis Struct for same molec –Equal, major, minor contributors Formal Charge (for each central atom) –Used to determine major Lewis Structure –Calc FC for the central atom(s) FC = e val – (e nb + ½e b ) H...... H C O H H C O H H H H

9. Determination of Formal Charge FC = e val – (e nb + ½e b ) H...... H C O H H H H FC C = 4 – [0 + (½8)] FC C = 4 – [2 + (½6)] = 0 = -1 FC O = 6 – [2 + (½4)] FC O = 6 – [2 + (½6)] = 0 = +1 the better structure has: 1- all atom’s FC as close to 0 as possible. 2- if not 0 then negative value is on the more electroneg element

10. Exceptions to Octet Rule Octet deficiencies –Odd electron species B, Be, and sometimes N form compounds with less than an octet

11. Exceptions to Octet Rule Octet deficiencies Odd electron species B, Be, and sometimes N form compounds with less than an octet Draw Lewis Structure for BeF 2

12. Expanded Octet Some species (3 rd period and beyond) exceed the octet rule Empty 3d sublevel (or higher) can accommodate extra e-s –Terminal atoms usually halogen or O Never occurs with 2 nd period elements –No d sublevel to house extra e-s

13. Molecular Geometry VSEPR Theory –Valence Shell Electron Pair Repulsion Theory All e- pairs (bonding and nonbonding) occupy orbitals (shells) All orbitals, being (-) charged repel each other, and push one another as far away as possible –All orbitals orient themselves as far apart as possible

14. Molecular Geometry Based on number of electron clouds around the central atom –Single, double, triple bonds, and nonbonding e- pairs all count as 1 cloud 2 to 6 pairs of e-s on central atom –Therefore 2 to 6 clouds around central atom Unshared (nonbonding) e- pairs affect the geometry of the molecule but not the orientation of the e- clouds about the central atom –Know descriptions and bond angles from tables 7.3 p 188 and 7.7 p 190

15. Nonbonding Clouds Molecular Geometry The nonbonding cloud is not seen as part of the molecule The geometry of the molecule and the geometry of the e- clouds are the same if there are no nonbonding clouds present The geometry of the molecule and the geometry of the e- clouds are different if there are nonbonding clouds present

16. Geometry of Molec with all bonding e- clouds

17. Effects of Nonbonding e- Clouds on Geometry

22. Structural Nonpolarity Bonds indicate molecule should be polar but it is not –Symmetrical molecule Linear, trig planar, tetrahed, triag bipyr, octa –Central atom bonded to 2 or more of the same atoms –Opposite pulls on e-s cancel each other

23. Structural Nonpolarity Water is polar because of the unequal pull on the electrons – the molecule in not symmetrical

24. Structural Nonpolarity Because of the equal attraction for the shared pair of e-s, and the symmetry the molecule, carbon dioxide is nonpolar

25. Hybridization Atomic orbital blend together and form new molecular orbitals –Called hybrid orbitals The same # of MO are formed as the # AO that blend together –1 s and 1 p AO form 2 sp MO –1 s and 2 p AO form 3 sp 2 –1 s and 3 p AO form 4 sp 3 –1 s and 3 p and 1 d AO form 5 sp 3 d –1 s and 3 p and 2 d AO form 6 sp 3 d 2

26. 2s These new orbitals are called hybrid orbitals The process is called hybridization This means is that the s and one p orbital are mixed together and form 2 sp hybrid molecular orbital. Formation of sp hybrid orbitals The combination of an s orbital and a p orbital produces 2 new orbitals called sp orbitals.

27. Formation of sp 2 hybrid orbitals

28. Formation of sp 3 hybrid orbitals

29. sp 3 d and sp 3 d 2 Orbitals sp 3 dsp 3 d 2

30. Sigma and Pi Bonds Sigma (  ) bond s are created by an end to end overlap of molecular orbitals –All single bonds are  bonds Pi bonds are formed by a side by side overlap of MO. The e-s are delocalized, moving more freely about both nuclei that e-s in a sigma bond. –Double bond = 1  bond, and 1  bond –Triple bond = 1  bond and 2  bonds.

31.  and  Bonds