In the secondary structure of proteins is due to hydrogen bonding (HB between the backbone oxygens and amide hydrogens. HB also occur in the tertiary structure of proteins.

1. Hydrogen Bonding and Life
Dr. K. Shahzad Baig
Memorial University of Newfoundland
(MUN)
Canada
Petrucci, et al. 2011. General Chemistry: Principles and Modern Applications. Pearson Canada Inc., Toronto, Ontario.
Tro, N.J. 2010. Principles of Chemistry. : a molecular approach. Pearson Education, Inc.

2. Hydrogen Bonding
a hydrogen atom that is
covalently bonded to a
highly electronegative
nonmetal atom in one
molecule …
leading to high partial
positive and partial
negative charges.
is simultaneously attracted
to other electronegative
nonmetal atom of a
neighboring molecule.

3. Hydrogen Bonding in Water
Hydrogen bonding arranges the water
molecules into an open hexagonal pattern.
“Hexagonal” is reflected in the crystal
structure. “Open” means reduced
density of the solid (vs. liquid).

4. H “Bonding” in Ethanol & Water
H “Bonding” in Acetic Acid

5. Properties Affected by Hydrogen Bonding
Molecules with H “bonding” have much higher than expected melting and boiling points.

6. H “Bonding” and Life

7. intramolecular
hydrogen bonds
can cause
proteins to take
a helical shape.

9. Liquids and Intermolecular Forces
Many properties of liquids can be attributed to intermolecular forces :
• Surface tension is the amount of work required to extend a liquid surface and is
usually expressed in J/m2.
• Adhesive forces are intermolecular forces between unlike molecules.
• Cohesive forces are intermolecular forces between like molecules.
• A meniscus is the interface between a liquid and the air above it.
• Viscosity is a measure of a liquid’s resistance to flow.

10. The liquid spreads, because adhesive forces are
comparable in strength to cohesive forces.

11. Water wets the glass
(adhesive forces) and
its attraction for
glass forms a
concave-up surface.
Meniscus Formation

12. The adhesive forces wet more and
more of the inside of the tiny tube,
drawing water farther up the tube.
Which oil flows more
readily?
Which oil has stronger
intermolecular forces
between its molecules?
Oil is mostly
hydrocarbons; what
kind of forces are these?

13. Vaporization and Condensation
Condensation
the reverse of vaporization.
Enthalpy of condensation (DHcondn)
the quantity of heat released for changing a gas to a liquid.
Enthalpy is a function of state: therefore, the total DH must be zero:
DHvapr + DHcondn = 0
DHcondn = –DHvapr
Vaporization
the conversion of a liquid to a gas.
Enthalpy of vaporization (ΔHvapr)
the quantity of heat absorbed to vaporize a given amount of liquid at a constant temperature.

14. Liquid–Vapor Equilibrium

15. Measuring Vapor Pressure
Dalton s law of partial pressures
Ideal gas Law
barometric pressure
Clausius Clapeyron Equation
enthalpy of vaporization of the liquid

16. Boiling and the Boiling Point
The pressure exerted by escaping molecules equals
that exerted by molecules of the atmosphere, and boiling is said to occur
The Critical Point
The critical point occurs:
• The density of the liquid decreases with increase in temperature, that of the vapor
increases, and eventually the two densities become equal.
• The surface tension of the liquid approaches zero.
The interface between the liquid and vapor becomes less distinct and eventually
disappears.
The temperature at the critical point is the critical temperature, Tc and
the pressure is the critical pressurePC

17. Types of Solids
Enthalpy of sublimation
the heat required to change one mole of a substance from solid state to gas
at a given combination of temperature and pressure,
usually standard temperature and pressure (STP).
Melting Point
the temperature at which it changes state from solid to liquid.
At the melting point the solid and liquid phase exist in equilibrium. The melting point
of a substance depends on pressure and is usually specified at a standard pressure
Heat of fusion
the energy needed for one gram of a solid to melt without any change in temperature.