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

2. Summary of Modern Atomic Theory
Atoms have an internal structure consisting of one or more subatomic particles: protons, neutrons, and electrons.

3. Summary of Modern Atomic Theory
Most of the mass of an atom is concentrated in the nucleus.
The nucleus contains one or more positively charged protons, and one or more neutrons with no electrical charge.

4. Summary of Modern Atomic Theory
One or more negatively charged electrons are in constant motion somewhere outside the nucleus.
The number of electrons is equal to the number of protons; the atom has no overall electrical charge.

5. Summary of Modern Atomic Theory
An atom is mostly free space because the volume of the nucleus and the electrons outside the nucleus are extremely small compared to the overall volume of the atom.

6. Summary of Modern Atomic Theory
Heisenberg Uncertainty Principle
It is not possible to determine both the position and the momentum of an electron.
Wave Function y
Describes the energy of an electron and the probability of finding the electron in a region around the nucleus.
Atomic Orbital
The probability distribution about one atomic nucleus (i.e., wave function = atomic orbital).
Amplitudes – numerical magnitudes
Signs – positive or negative
Nodes – values of wavefunction equals zero (given by quantum numbers)

7. Summary of Modern Atomic Theory
Heisenberg Uncertainty Principle
It is not possible to determine both the position and the momentum of an electron.
Wave Function y
Describes the energy of an electron and the probability of finding the electron in a region around the nucleus.
Atomic Orbital
The probability distribution about one atomic nucleus (i.e., wave function = atomic orbital).
Amplitudes – numerical magnitudes
Signs – positive or negative
Nodes – values of wavefunction equals zero (given by quantum numbers)

8. Summary of Modern Atomic Theory
Heisenberg Uncertainty Principle
It is not possible to determine both the position and the momentum of an electron.
Wave Function y
Describes the energy of an electron and the probability of finding the electron in a region around the nucleus.
Atomic Orbital
The probability distribution about one atomic nucleus (i.e., wave function = atomic orbital).
Amplitudes – numerical magnitudes
Signs – positive or negative
Nodes – values of wavefunction equals zero (given by quantum numbers)

9. Summary of Modern Atomic Theory
Heisenberg Uncertainty Principle
It is not possible to determine both the position and the momentum of an electron.
Wave Function y
Describes the energy of an electron and the probability of finding the electron in a region around the nucleus.
Atomic Orbital
The probability distribution about one atomic nucleus (i.e., wave function = atomic orbital).
Amplitudes – numerical magnitudes
Signs – positive or negative
Nodes – values of wave function equals zero (given by quantum numbers)

10. Atomic Orbitals
s orbital
p orbitals

11. Hybridization
In chemistry, hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals suitable for the qualitative description of atomic bonding properties.
Hybridised orbitals are very useful in the explanation of the shape of molecular orbitals for molecules.

12. Hybrid Atomic Orbitals
hybrid bonding shape rotation bond
sp3() head-head tetrahedral free single
sp2 () sideways triangular rigid double
sp () sideways linear rigid triple

13. Carbon
Atomic Number = 6

14. Carbon
Atomic Number = 6

15. Oxygen
Atomic Number = 8

16. Oxygen
Atomic Number = 8

17. Chemical Bonding Chemical Bonds Valence Electrons
The forces holding atoms together in compounds.
Valence Electrons
The electrons in the outer shell.
Lewis Dot Representation of Atoms
Dots around the chemical symbol of an atom represent the valence electrons.

18. Chemical Bonding Chemical Bonds Valence Electrons
The forces holding atoms together in compounds.
Valence Electrons
The electrons in the outer shell.
Lewis Dot Representation of Atoms
Dots around the chemical symbol of an atom represent the valence electrons.

19. Chemical Bonding Chemical Bonds Valence Electrons
The forces holding atoms together in compounds.
Valence Electrons
The electrons in the outer shell.
Lewis Dot Representation of Atoms
Dots around the chemical symbol of an atom represent the valence electrons.

20. Examples

21. Examples

22. Examples

23. Examples

24. Examples

25. Examples

26. Examples

27. Examples

28. Examples

29. Molecular Orbital Theory
Molecular orbitals – delocalized over entire molecule.
First Principle
The total number of molecular orbitals is always equal to the total number of atomic orbitals contributed by the atoms that have combined.

30. Molecular Orbitals for H2
Bonding molecular orbital
addition of two atomic orbitals, leads to the probability of finding an e- between the atoms.
Antibonding molecular orbital
substration of one atomic orbital from the other, leads to reduced probability of finding an e- between the nuclei, increased in other regions.

31. Molecular Orbital Theory
Second Principle
The bonding molecular orbital is lower in energy than the parent orbitals, and the antibonding orbital is higher in energy.
Third Principle
The electrons of the molecule are assigned to orbitals of successively higher energy (according to Pauli exclusion principle and the Hund’s rule).

32. The Ionic Bond Transfer of Electrons from One Atom to Another Example:
Sodium chloride

33. The Ionic Bond
The electrostatic attraction between oppositely charged ions.

34. The Covalent Bond
Some atoms do not transfer electrons from one atom to another to form ions.
Instead they form a chemical bond by sharing pairs of electrons between them.
A covalent bond consists of a pair of electrons shared between two atoms.

35. The Covalent Bond
Some atoms do not transfer electrons from one atom to another to form ions.
Instead they form a chemical bond by sharing pairs of electrons between them.
A covalent bond consists of a pair of electrons shared between two atoms.

36. The Covalent Bond
Some atoms do not transfer electrons from one atom to another to form ions.
Instead they form a chemical bond by sharing pairs of electrons between them.
A covalent bond consists of a pair of electrons shared between two atoms.

37. Hydrogen, H2

38. Fluorine, F2

39. Fluorine, F2

40. Fluorine, F2

41. Nitrogen, N2

42. Nitrogen, N2

43. Nitrogen, N2
Carbon Dioxide, CO2

44. Nitrogen, N2
Carbon Dioxide, CO2

45. Molecular Orbitals for He2
He2 has no net stability – two He atoms have no tendency to combine.