Intermolecular forces and intramolecular forces

Intermolecular and intramolecular forces

1. INTERMOLECULAR
FORCES

2. Molecules experience two types of forces:
intramolecular (or bonding) and
intermolecular (or nonbonding)
Intramolecular attraction
Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd.
Silberberg, M. 2010. Principles of General Chemistry. 2
nd
ed. New York: McGraw-
Hill.

3. Intramolecular forces hold atoms together in
a single molecule
• strong force
• types
a. ionic bond
b. covalent bond
c. metallic bond
•responsible for the
chemical properties
of the substance

4. Intermolecular forces exist between the molecules
• weak force
• influence the physical properties of the substance
* note: the molecules need not be identical

5. Intermolecular Forces of
Attraction
(IMFA)

6. Opposites Attract

7. Opposites Attract

8. Types of IMFA
•Ion-dipole force
•Dipole-dipole force
* London dispersion force (LDF)
•Hydrogen bonding
• permanent charge separation
* momentary charge separation

9. Ion-dipole force exists between an ion and the
partial charge on the end of a polar molecule

11. Dipole-dipole force exists between polar
molecules
Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8
th
ed. Phils: Pearson Education Asia Pte. Ltd.

12. London dispersion force (LDF) exists between all
molecules, including nonpolar molecules
•electrons constantly move
•at a certain instance, more electrons can be
concentrated in one side of a molecule over
another
•this gives temporary polarity to the molecule
Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8
th
ed. Phils: Pearson Education Asia Pte. Ltd.

14. Hydrogen bonding is a special type of dipole-dipole
interaction between hydrogen directly bonded to
F, O, or N and F, O, or N atom
Brown, , E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8
th
ed. Phils: Pearson Education Asia Pte. Ltd.
Chang, R. 2002. Chemistry 7
th
ed. Singapore: McGraw-Hill.
– covalent bond
. . . hydrogen bond

15. Hydrogen bonding is unusually strong
•F, O, and N are highly electronegative, thus
bond between hydrogen and F, O, or N is
highly polar
F—H O—H N—H
•hydrogen has no inner core electrons,
making it bare and relatively small
•being small, H can come close to F, O, or
N, resulting to a strong bond
Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8
th
ed. Phils: Pearson Education Asia Pte. Ltd.

16. Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8
th
ed. Phils: Pearson Education Asia Pte. Ltd.
Intermolecular
forces
Intramolecular
force
Increasing strength

17. Determine the IMFA/s present in the following
•Br
2
–LDF
•KCl in H
2O
–LDF, ion-dipole,
hydrogen bonding
•CH
3OH
–LDF, hydrogen bonding
C O
H
H
H
H

18. Determine the IMFA/s present in the following
•H
2S
–LDF, dipole-dipole
•CH
3OCH
3
–LDF, dipole-dipole
OCC
H
H
H
H
H
H

19. IMFA and the states of matter

20. Chang, R. 2002. Chemistry 7
th
ed. Singapore: McGraw-Hill.

21. Gas molecules have weak IMFAs
•interaction between the molecules is
minimal, and so gas molecules fill a
container
•distances between gas molecules
are so great, and so gases are
highly compressible and have low
densities
Chang, R. 2002. Chemistry 7
th
ed. Singapore: McGraw-Hill.

22. Liquid molecules have stronger IMFAs
•molecules are held together by
one or more types of attractive
forces, and so liquid molecules
have definite volume but indefinite
shape
•distances between liquid
molecules are small, and so
liquids are slightly compressible
and have high densities
Chang, R. 2002. Chemistry 7
th
ed. Singapore: McGraw-Hill.

23. Solid molecules have very strong IMFAs
•molecules are held rigidly in
position, and so solid molecules
have definite volume and definite
shape
•distances between solid molecules
are even smaller than in liquids,
and so solids are almost
incompressible and have high
densities
Chang, R. 2002. Chemistry 7
th
ed. Singapore: McGraw-Hill.

24. Chang, R. 2002. Chemistry 7
th
ed. Singapore: McGraw-Hill.

25. If the molecules have enough energy, they can
overcome the IMFAs and change from one state
of matter to another
* Energy is the capacity to do work or to produce
change. It may take different forms, and heat is one of
them.
Chang, R. 2002. Chemistry 7
th
ed. Singapore: McGraw-Hill.

26. When a liquid boils, the weak IMFAs are overcome,
but the strong covalent bonds holding the atoms
together within each molecule remain unaffected
* The same is true when a solid turns into liquid or gas
Silberberg, M. 2010. Principles of General Chemistry. 2
nd
ed. New York: McGraw-Hill.

28. The ice layer that forms on the surface (and not
at the bottom) of a lake insulates the water
beneath and maintains a high enough
temperature to sustain aquatic life
Chang, R. 2002. Chemistry 7
th
ed. Singapore: McGraw-Hill.

29. A soap molecule can clean because its two
ends are strikingly different
McMurry, J. 2011. Organic Chemistry with Biological Applications. 2
nd
ed. California: Brooks/Cole.
Ionic
Water-loving (aka hydrophilic)
Nonpolar
Water-hating (aka hydrophobic)
Oil-loving

30. The hydrocarbon tails interact with the oil to
form hydrophobic balls, while the ionic
heads stick out and interact with water
McMurry, J. 2011. Organic Chemistry with Biological Applications. 2
nd
ed. California: Brooks/Cole.
micelle

31. Compared to tissue, blotting paper is better
at removing oil from the face
http://badkittyexoticwear.com/shop/facecareoilblottingpaper-p-1617.html
http://pics.drugstore.com/prodimg/68807/300.jpg

32. To cook bulalo, one needs to boil beef in water
with salt. During the process, the fat from the
meat is seen floating on top of the broth,
while the salt is not visible.
http://norecipes.com/blog/2009/06/11/bulalo-recipe/