1. Atomic & Molecular Bonding

2. Ionic Covalent Metallic Weak Forces Types of Bonding:
strong bonds (“primary”)
(“secondary”)

3. Valence Electrons
Those electrons that participate in bonding between atoms – usually the electrons with the highest energies.

4. Atomic Structure – planetary model
Hydrogen
Helium
Oxygen

5. Orbital
The quantum-mechanical description of an electron, which includes the electron’s energy and its time-averaged distribution in space.

6. z y x Quantum mechanical view: gives time averaged probability
of an electron’s
position. z
there’s a higher
probability this
electron is nearer
the atom’s nucleus. y
there’s a lower
probability that this
electron is farther
from the atom’s
nucleus. x

7. z y x Quantum mechanical result: some valence electrons have
a time-averaged probability that
is stronger in some directions
than in others. z
Valence electrons are
much more likely to be
found in these directions. y x

8. Ionic bonding:
A primary bond due to electrostatic attraction between oppositely charged ions.

9. Ionic bonding – electronegativity:
Transfer of valence
electrons Na Cl

10. Ionic bonding – electronegativity:
Na+
Cl-

11. Ionic bonding – electronegativity:

12. Ionic bonding – electronegativity:

13. Ionic bonding – electronegativity:
Electronegativity: The relative tendency of atoms to accept electrons.

14. Ionic bonding – charge balance:
Cl -
Na+
Attraction of ions with unlike charges
Integrity of the ensemble depends on alternating charge
Moving an ion will disrupt bonding

15. A primary bond that arises when two atoms share valence electrons.
Covalent bonds:
A primary bond that arises when two atoms share valence electrons.

16. Si O Si O

17. O O Si O O

18. Metallic bonds:
A primary bond that can be thought of as the electrostatic attraction between an electron gas of valence electrons and positively charged ion cores.

19. Metallic bonding – the electron gas:
free valence electrons
not attached to a given atom
conceived as an “electron gas” + +
electron gas + + +

20. Metallic bonding – the electron gas:
average electron midway
between positive ions +
bond is “omni-directional”
- ions can move out of
position without the bond
breaking + + +
virtual charge balance keeps
the ensemble together +
electron gas

21. Metallic bonding: bonds not dependent on direction – atoms can be displaced+ + - + +
electron gas + + + + + - + + + + + + + + + + +

22. Metallic: non-directional Covalent: often highly directional
Bond directionality
Metallic: non-directional
Covalent: often highly directional
Ionic: directional in the sense that bonding depends
on a precise charge
balance

23. Covalent bonding: strong in particular directions, break if atom displaced from that direction

24. Metallic: can be ductile Covalent: brittle Ionic: brittle
Bond directionality
Metallic: can be ductile
Covalent: brittle
Ionic: brittle

25. Bonding
Substance
KJ/mol
Melting Pt. oC
Ionic
NaCl
640
801
MgO
1000
2800
Covalent Si
450
1410
C (diamond)
713
> 3550
Metallic Hg 68
- 39 Al
324
660 Fe
406
1538 W
849
3410

26. Bonding
Substance
KJ/mol
Melting Pt. oC
van der Waals Ar
7.7
- 189
Cl 2 31
- 101
Hydrogen
NH3 35
- 78
H2O 51

27. Secondary Bonds – Intermolecular Forces:
van der Waals
dipole-dipole forces
London forces
Hydrogen Bonds

28. van der Waals forces: dipole-dipole forcesH + - Cl
Here molecules are permanent dipoles with net negative charge at one end and net positive charge at the other.

29. van der Waals forces: induced dipole+ - + -
Molecules with strong dipole moments can induce dipoles in nearby atoms and molecules + - - +

30. van der Waals forces: London forces+ - + -
Average Charge Distribution
but in Quantum mechanics the above has a small probability of occurring
London forces help the weak attraction between atoms and molecules that have no permanent dipole moment. The forces that arise between molecules from with such randomly appearing dipoles are called “London forces.”

31. Hydrogen Bonding: Oxygen - + H H hydrogen bonds hydrogen bonds
The single electron around a hydrogen atom participates in bonding leaving behind the positively charged proton. The concentration of positive charge around the proton will be attracted toward areas of negative charge.
In this sketch hydrogen bonds are causing water molecules to align.

32. Forces between polymer molecules: role of hydrogen bonds
Particularly strong hydrogen bond arise between H+ and, strongly and relatively small electronegative atoms such as Cl, O, and F.
PVC - polyvinylchloride

33. Forces between polymer molecules: role of hydrogen bonds
weak bonding
allows molecules
to slide with
respect to
on another C l H x x x x C l H
broken
bond
PVC - polyvinylchloride

34. The End