1. The Chemistry of Life Biology is a multidisciplinary science.
Living organisms are subject to basic laws of physics and chemistry.
One example is the bombardier beetle, which uses chemistry to defend itself.

2. Atoms of elements play important roles in biology
What element is lacking in her diet?

3. Atoms combine to make molecules
The bonds between atoms of the same molecule are intramolecular bonds. The three types of intramolecular bonds are:
Covalent Bonds
Ionic Bonds
Polar Covalent Bonds

4. 1. Covalent Bonds
The bond is formed by sharing a pair of valence electrons between two atoms.
The bond can be represented in many ways.
Hydrogen (H2)
Name
(molecular
formula)
Electron-
shell
diagram
Structural
formula
Space-
filling
model

5. 2. Polar Covalent Bonds
This bond occurs when a pair of valence electrons is unequally shared between two atoms.
The atom with a larger nucleus attracts the electron more and has a slightly negative charge.
The other atom is slightly positive.

6. Sodium chloride (NaCl)
3. Ionic Bond
Formed by the transfer of an electron from atom to atom. This results in the formation of positive cations, and negative anions. Ions are held together by electrostatic attraction. Na
Sodium atom
(an uncharged
atom) Cl
Chlorine atom
Na+
Sodium ion
(a cation)
Cl–
Chlorine ion
(an anion)
Sodium chloride (NaCl)

7. Properties of Covalent Bonds
Pure Covalent Bonds
Results from largely equal sharing of electrons.
Happens when bond partners have similar electronegativities or an electronegativity difference of <0.5
Polar Covalent Bonds
Results from unequal sharing of electrons.
Happens when bond partners have electronegativity differences between 0.5 and 1.6

8. The Role of Electronegativity
Electronegativity is a measure of the strength with which an atom can attract electrons and can be found on a periodic table.
The electronegativity difference between two atoms is calculated by subtracting the smaller value from the larger value.

9. Bond Types and Electronegativity
A difference of < 0. 5  covalent bond
A difference of 0.5 – 1.6  polar covalent bond
A difference of > 1.6  ionic bond

10. Bonds in Water Oxygen electronegativity = 3.44
Hydrogen electronegativity = 2.2
Difference
3.44 – 2.2 = 1.24
Bond Type 
Polar covalent
In a water molecule the oxygen is slightly negatively charged. H O
H2O + –

11. Inter- Molecular Interactions
The properties of molecules can influence their interactions with other molecules. These are weaker bonds than intramolecular bonds.
hydrogen bonding
dipole-dipole interactions
London/dispersion force

12. Water: A special molecule
a) Hydrogen bonding
Effects: cohesion, adhesion, surface tension. More energy is needed to break hydrogen bonds than other intermolecular bonds, which gives water a high specific heat capacity.
b) Density
Effects: Ice is less dense so it floats, insulating water underneath.

13. Water: A special molecule
c) Polar nature of the bond
Effects: as a solvent, water allows polar molecules and ionic compounds to dissolve due to water’s polarity
d) Dissociation of intramolecular bonds
Effects: 1 in 107 water molecules dissociates to form H+ and OH- ions.
This is a pH of 7 = NEUTRAL.

14. Functional Groups Functional groups are parts of larger molecules.
They greatly influence biological reactivity.

15. Functional Groups Hydroxyl – alcohols Carboxyl – acids Amino – bases
Carbonyl – aldehydes and ketones

16. Functional Groups
One biologically important functional group missing from this list is sulfhydryl, which contains sulphur. The name of molecules with this functional group is thiol. The ‘R’ represents the rest of the molecule.

17. Functional Groups
Sulphur forms relatively strong intermolecular bonds with other sulphurs. This is important to forming the 3D structure of proteins.

18. Extra slides for students without chemistry background

19. FUNCTIONAL PROPERTIES
LE 4-10aa
STRUCTURE
(may be written HO—)
Ethanol, the alcohol present in
alcoholic beverages
NAME OF COMPOUNDS
FUNCTIONAL PROPERTIES
Alcohols (their specific names
usually end in -ol)
Is polar as a result of the
electronegative oxygen atom
drawing electrons toward itself.
Attracts water molecules, helping
dissolve organic compounds such
as sugars (see Figure 5.3).

20. STRUCTURE EXAMPLE NAME OF COMPOUNDS Acetone, the simplest ketone
LE 4-10ab
Acetone, the simplest ketone
STRUCTURE
EXAMPLE
Acetone, the simplest ketone
Propanal, an aldehyde
NAME OF COMPOUNDS
Ketones if the carbonyl group is
within a carbon skeleton
FUNCTIONAL PROPERTIES
Aldehydes if the carbonyl group is
at the end of the carbon skeleton
A ketone and an aldehyde may
be structural isomers with
different properties, as is the case
for acetone and propanal.

21. LE 4-10ac
STRUCTURE
EXAMPLE
Acetic acid, which gives vinegar
its sour taste
NAME OF COMPOUNDS
FUNCTIONAL PROPERTIES
Carboxylic acids, or organic acids
Has acidic properties because it is
a source of hydrogen ions.
The covalent bond between
oxygen and hydrogen is so polar
that hydrogen ions (H+) tend to
dissociate reversibly; for example,
Acetic acid
Acetate ion
In cells, found in the ionic form,
which is called a carboxylate group.

22. LE 4-10ba
STRUCTURE
EXAMPLE
Glycine
Because it also has a carboxyl
group, glycine is both an amine and
a carboxylic acid; compounds with
both groups are called amino acids.
NAME OF COMPOUNDS
FUNCTIONAL PROPERTIES
Amine
Acts as a base; can pick up a
proton from the surrounding
solution:
(nonionized)
(ionized)
Ionized, with a charge of 1+,
under cellular conditions

23. STRUCTURE EXAMPLE NAME OF COMPOUNDS
LE 4-10bb
STRUCTURE
EXAMPLE
(may be written HS—)
Ethanethiol
NAME OF COMPOUNDS
FUNCTIONAL PROPERTIES
Thiols
Two sulfhydryl groups can
interact to help stabilize protein
structure (see Figure 5.20).

24. STRUCTURE EXAMPLE NAME OF COMPOUNDS
LE 4-10bc
STRUCTURE
EXAMPLE
Glycerol phosphate
NAME OF COMPOUNDS
FUNCTIONAL PROPERTIES
Organic phosphates
Makes the molecule of which it
is a part an anion (negatively
charged ion).
Can transfer energy between
organic molecules.