1. Lecture 2 Chemical Bonds: Atomic Orbital Theory and Molecular Orbital Theory
Dr. A.K.M. Shafiqul Islam

2. 1s and 2s Atomic Orbitals
Figure: UN
Title:
1s and 2s Atomic orbitals.
Caption:
An orbital is a three-dimensional region around the nucleus where there is a high probability of finding an electron. The node is the region where the probability of finding an electron falls to zero.
An orbital is a three-dimensional region around the nucleus where there is a high probability of finding an electron. The node is the region where the probability of finding an electron falls to zero.

3. Nodal planes for p orbitals
Figure: UN
Title:
Nodal planes for p orbitals.
Caption:
p Atomic orbitals have two lobes and are dumbbell-shaped. The two lobes are of opposite phase.
p Atomic orbitals have two lobes and are dumbbell-shaped.
The two lobes are of opposite phase. + and – sign are not opposite charge.

4. Degenerate 2p atomic orbitals
Figure: UN
Title:
Degenerate 2p atomic orbitals.
Caption:
The 2p orbitals lie along the x, y, and z axes. Each p orbital contains up to 2 electrons.
The 2p orbitals lie along the x, y, and z axes. Each p orbital contains up to 2 electrons.

5. Sigma bonds for a hydrogen molecule
Figure: UN
Title:
Sigma bonds for a hydrogen molecule.
Caption:
Sigma bonds can form where two s orbitals overlap. The sigma bond is cylindrically symmetrical.
Sigma bonds can form where two s orbitals overlap. The sigma bond is cylindrically symmetrical.

6. Bond length for hydrogen atoms
Figure: 01-02
Title:
Figure Bond length for hydrogen atoms.
Caption:
The change in potential energy that occurs as two 1s atomic orbitals approach each other. The internuclear distance at minimum energy is the length of the hydrogen-hydrogen covalent bond.
The change in potential energy that occurs as two 1s atomic orbitals approach each other. The internuclear distance at minimum energy is the length of the hydrogen-hydrogen covalent bond.

7. Atomic and molecular orbitals of H and H2
Figure: 01-04
Title:
Figure Atomic and molecular orbitals of H and H2.
Caption:
Before covalent bond formation, each electron is in an atomic orbital. After covalent bond formation, both electrons are in the bonding molecular orbital. The antibonding molecular orbital is empty.
Before covalent bond formation, each electron is in an atomic orbital. After covalent bond formation, both electrons are in the bonding molecular orbital. The antibonding molecular orbital is empty.

8. p Orbital bonding (end-to-end
Figure: 01-05
Title:
Figure p Orbital bonding (end-to-end).
Caption:
End-on overlap of two p orbitals to form a sigma bonding molecular orbital and a sigma antibonding molecular orbital.
End-on overlap of two p orbitals to form a sigma bonding molecular orbital and a sigma antibonding molecular orbital.

9. Figure: 01-06
Title:
Figure p Orbital bonding (side-to-side).
Caption:
Side-to-side overlap of two parallel p orbitals to form a pi bonding molecular orbital and a pi antibonding molecular orbital.
Side-to-side overlap of two parallel p orbitals to form a pi bonding molecular orbital and a pi antibonding molecular orbital.

10. MO diagram for MOs made from p atomic orbitals.
p Atomic orbitals can overlap end-on to form sigma bonding and antibonding molecular orbitals.
The bonding combination has less energy than the antibonding combination.
p Atomic orbitals can also overlap side-to-side to form pi bonding and antibonding molecular orbitals.
The relative energies are bonding sigma < bonding pi < antibonding pi < antibonding sigma.
Figure: 01-07
Title:
Figure MO diagram for MOs made from p atomic orbitals.
Caption:
p Atomic orbitals can overlap end-on to form sigma bonding and antibonding molecular orbitals. The bonding combination has less energy than the antibonding combination. p Atomic orbitals can also overlap side-to-side to form pi bonding and antibonding molecular orbitals. The relative energies are bonding sigma < bonding pi < antibonding pi < antibonding sigma.

11. Figure: 01-08
Title:
Figure Carbon-oxygen pi bond formation.
Caption:
Side-to-side overlap of a p atomic orbital from carbon with a p atomic orbital from oxygen results in pi bonding and pi antibonding molecular orbitals.

12. Figure: UN
Title:
Models of methane.
Caption:
The ball-and-stick model, the space-filling model, and the electrostatic potential map are shown for methane.

13. The Electronic Configurations of the Smallest Atoms
Figure: 01-T02
Title:
Table The Electronic Configurations of the Smallest Atoms.
Caption:
The electronic configuration is based upon the number of valence electrons. s can have a maximum of 2 electrons; p can have a maximum of 6 electrons. For the p orbitals, the px, py, and pz must have one electron each before another electron is placed in the shell.

14. sp3 Hybridization
Figure: UN
Title:
sp3 Hybridization.
Caption:
A carbon atom has a 2s electron promoted to a 2p orbital. Promotion of a 2s electron to a 2p orbital is needed so that carbon has four unpaired electrons.
A carbon atom has a 2s electron promoted to a 2p orbital. Promotion of a 2s electron to a 2p orbital is needed so that carbon has four unpaired electrons.

15. sp3 Hybridization.
Figure: UN
Title:
sp3 Hybridization.
Caption:
One s and three p orbitals are hybridized to form an sp3-hybridized orbital.
One s and three p orbitals are hybridized to form an sp3-hybridized orbital

16. Formation of sp3 hybrid orbital
Figure: 01-09
Title:
Figure Formation of sp3 hybrid orbital.
Caption:
The s orbital adds to one lobe of the p orbital and subtracts from the other lobe of the p orbital.
The s orbital adds to one lobe of the p orbital and subtracts from the other lobe of the p orbital.

17. Formation of four sp3 hybrid orbitals
Figure: 01-10
Title:
Figure Formation of four sp3 hybrid orbitals.
Caption:
One s atomic orbital combines with three p atomic orbitals to make four sp3 hybrid orbitals.
One s atomic orbital combines with three p atomic orbitals to make four sp3 hybrid orbitals.

18. Structure of methane
Figure: 01-11
Title:
Figure Structure of methane.
Caption:
(a) Four sp3 orbitals are directed toward the corners of a tetrahedron causing each bond angle to be degrees. (b) An orbital picture of methane showing the overlap of each sp3 orbital of the carbon with the s orbital of hydrogen.
Four sp3 orbitals are directed toward the corners of a tetrahedron causing each bond angle to be degrees.
An orbital picture of methane showing the overlap of each sp3 orbital of the carbon with the s orbital of hydrogen.

19. Bonds in ethane
Figure: UN
Title:
Bonds in ethane.
Caption:
The two carbon atoms in ethane are tetrahedral. Each carbon uses four sp3 orbitals to form four covalent bonds.
The two carbon atoms in ethane are tetrahedral. Each carbon uses four sp3 orbitals to form four covalent bonds.

20. Bonding in ethane
Figure: 01-12
Title:
Figure Bonding in ethane.
Caption:
The carbon-carbon bond is formed by sp3-sp3overlap, and each carbon-hydrogen bond is formed by sp3-s overlap.
The carbon-carbon bond is formed by sp3-sp3overlap, and each carbon-hydrogen bond is formed by sp3-s overlap.

21. Structure of ethane
Figure: UN
Title:
Structure of ethane.
Caption:
The two carbons in ethane are tetrahedral. Each carbon uses four sp3 atomic orbitals to form four covalent bonds.
The two carbons in ethane are tetrahedral. Each carbon uses four sp3 atomic orbitals to form four covalent bonds.

22. Orbital diagram for ethane
Figure: 01-13
Title:
Figure Orbital diagram for ethane.
Caption:
End to end overlap of two sp3 hybrid orbitals on the carbon atoms in ethane form sigma bonding and antibonding molecular orbitals.
End to end overlap of two sp3 hybrid orbitals on the carbon atoms in ethane form sigma bonding and antibonding molecular orbitals.

23. Ethene, ethylene Ethene contains a carbon-carbon double bond.
Figure: UN
Title:
Ethene, ethylene.
Caption:
Ethene contains a carbon-carbon double bond.
Ethene contains a carbon-carbon double bond.

24. sp2 Hybridization
Figure: UN
Title:
sp2 Hybridization.
Caption:
A carbon atom has a 2s electron promoted to a 2p orbital. One s and two p orbitals are hybridized to form an sp2-hybridized orbital.
A carbon atom has a 2s electron promoted to a 2p orbital. One s and two p orbitals are hybridized to form an sp2-hybridized orbital.

25. sp2 Hybrid orbitals The three sp2 hybrid orbitals lie in a plane.
Figure: 01-14
Title:
Figure sp2 Hybrid orbitals.
Caption:
(a) The three sp2 hybrid orbitals lie in a plane. (b) The unhybridized p orbital is perpendicular to the plane.
The three sp2 hybrid orbitals lie in a plane.
The unhybridized p orbital is perpendicular to the plane.

26. Structure of a double bond
Figure: 01-15
Title:
Figure Structure of a double bond.
Caption:
(a) One C-C bond in ethene is a sigma bond formed by sp2-sp2 overlap, and the C-H bonds are formed by sp2-s overlap. (b) The second C-C bond is a pi bond formed by the side-to-side overlap of a p orbital of one carbon with a p orbital of the other carbon. (c) There is an accumulation of electron density above and below the plane containing the two carbons and four hydrogens.
One C-C bond in ethene is a sigma bond formed by sp2-sp2 overlap, and the C-H bonds are formed by sp2-s overlap.
The second C-C bond is a pi bond formed by the side-to-side overlap of a p orbital of one carbon with a p orbital of the other carbon.
There is an accumulation of electron density above and below the plane containing the two carbons and four hydrogens.

27. Lewis structure, ball-and-stick model, space-filling model, and electrostatic potential map of ethene
Figure: UN
Title:
Lewis structure, ball-and-stick model, space-filling model, and electrostatic potential map of ethene.
Caption:
Ethene consists of a carbon-carbon double bond and four carbon-hydrogen single (sigma) bonds.
Ethene consists of a carbon-carbon double bond and four carbon-hydrogen single (sigma) bonds

28. Ethyne, acetylene
Figure: UN
Title:
Ethyne, acetylene.
Caption:
Ethyne contains a carbon-carbon triple bond and two carbon-hydrogen single bonds.
Ethyne contains a carbon-carbon triple bond and two carbon-hydrogen single bonds.

29. sp Hybridization
Figure: UN
Title:
sp Hybridization.
Caption:
A carbon atom has a 2s electron promoted to a 2p orbital. One s orbital and one p orbital are hybridized to form an sp-hybridized orbital.
A carbon atom has a 2s electron promoted to a 2p orbital. One s orbital and one p orbital are hybridized to form an sp-hybridized orbital.

30. sp-Hybridized carbon atom
Figure: 01-16
Title:
Figure sp-Hybridized carbon atom.
Caption:
The two sp orbitals are oriented 180 degrees away from each other, perpendicular to the two unhybridized p orbitals.
The two sp orbitals are oriented 180 degrees away from each other, perpendicular to the two unhybridized p orbitals.

31. Orbital structure of ethyne
The C-C sigma bond in ethyne is formed by sp-sp overlap, and the C-H bonds are formed by sp-s overlap. The carbon atoms and the atoms bonded to them are in a straight line.
The two carbon-carbon pi bonds are formed by the side-to-side overlap of the p orbitals of one carbon with the p orbitals of the other carbon.
The triple bond has an electron-dense region above and below and in front of and in back of the internuclear axis of the molecule.
Figure: 01-17
Title:
Orbital structure of ethyne.
Caption:
(a) The C-C sigma bond in ethyne is formed by sp-sp overlap, and the C-H bonds are formed by sp-s overlap. The carbon atoms and the atoms bonded to them are in a straight line. (b) The two carbon-carbon pi bonds are formed by the side-to-side overlap of the p orbitals of one carbon with the p orbitals of the other carbon. (c) The triple bond has an electron-dense region above and below and in front of and in back of the internuclear axis of the molecule.

32. A carbon-carbon triple bond consists of three pairs of electrons.
Lewis structure, ball-and-stick model, space-filling model, and electrostatic potential map of ethyne
Figure: UN
Title:
Lewis structure, ball-and-stick model, space-filling model, and electrostatic potential map of ethyne.
Caption:
A carbon-carbon triple bond consists of three pairs of electrons.
A carbon-carbon triple bond consists of three pairs of electrons.

33. The carbon only has six electrons around it in a methyl cation
Orbital depiction, ball-and-stick models, and an electrostatic potential map of the methyl cation
Figure: UN
Title:
Orbital depiction, ball-and-stick models, and an electrostatic potential map of the methyl cation.
Caption:
The carbon only has six electrons around it in a methyl cation.
The carbon only has six electrons around it in a methyl cation

34. The carbon in a methyl radical has seven electrons
Orbital depiction, ball-and-stick models, and an electrostatic potential map of the methyl radical
Figure: UN
Title:
Orbital depiction, ball-and-stick models, and an electrostatic potential map of the methyl radical.
Caption:
The carbon in a methyl radical has seven electrons.
The carbon in a methyl radical has seven electrons

35. The carbon in the methyl anion has eight electrons.
Orbital depiction, ball-and-stick models, and an electrostatic potential map of the methyl anion
Figure: UN
Title:
Orbital depiction, ball-and-stick models, and an electrostatic potential map of the methyl anion.
Caption:
The carbon in the methyl anion has eight electrons.
The carbon in the methyl anion has eight electrons.

36. sp3 Hybridization in water
Figure: UN
Title:
sp3 Hybridization in water.
Caption:
One s and three p orbitals are hybridized to form an sp3-hybridized orbital.
One s and three p orbitals are hybridized to form an sp3-hybridized orbital.

37. The oxygen is sp3 hybridized
Orbital depiction, ball-and-stick model, and an electrostatic potential map of water
Figure: UN
Title:
Orbital depiction, ball-and-stick model, and an electrostatic potential map of water.
Caption:
The oxygen is sp3 hybridized.
The oxygen is sp3 hybridized

38. sp3 Hybridization in ammonia
Figure: UN
Title:
sp3 Hybridization in ammonia.
Caption:
One s and three p orbitals are hybridized to form an sp3-hybridized orbital.
One s and three p orbitals are hybridized to form an sp3-hybridized orbital.

39. The nitrogen in ammonia is sp3 hybridized
Orbital depiction, ball-and-stick model, and electrostatic potential map of ammonia
Figure:
Title:
Orbital depiction, ball-and-stick model, and electrostatic potential map of ammonia.
Caption:
The nitrogen in ammonia is sp3 hybridized.
The nitrogen in ammonia is sp3 hybridized