The Chemistry of Life
Life is composed of MATTER (anything that occupies space and has mass)
Matter is composed of chemical ELEMENTS (substances that cannot be broken down
into other substances)
About 92 elements that occur in nature, such as
oxygen, carbon, copper
COMPOUNDS - substances containing two or more
elements (ex. chlorophyll)
ATOMS - smallest unit of matter that still retains
the properties of an element, each element consists
of one type of atom
Recall the structure of the atom from chemistry
Elements in the Human Body
Name
Symbol
Percent of
Weight
Oxygen
O
65.0
Carbon
C
18.5
Hydrogen
H
9.5
Nitrogen
N
3.3
Calcium
Ca
1.5
Phosphorous
P
1.0
Potassium
K
0.4
Sulfur
S
0.3
Sodium
Na
0.2
Chlorine
Cl
0.2
Magnesium
Mg
0.1
Webelements - interactive periodic
table
Nucleus of the atom contains protons (positive) and neutrons (neutral) and the shell
of the atom contains electrons (negative)
All atoms of a particular element have the same number of protons - this is the
element’s ATOMIC NUMBER
MASS NUMBER or ATOMIC WEIGHT- refers to the sum of the protons and neutrons in
the nucleus.
ISOTOPES - variant forms of an element, these forms differ in the number of
neutrons they contain
Isotopes of Carbon
Carbon-12
Carbon-13
Carbon-14
Protons
6
6
6
Neutrons
6
7
8
Electrons
6
6
6
Note that the number after the
carbon refers to the sum of its
protons and neutrons
All have 6 protons, else they
wouldn’t be carbon at all.
Carbon-14 is an unstable isotope - or radioactive - which can pose a danger to
organisms, or can be used in ways that benefit us.
Examples - some radioactive isotopes are used to trace the path of elements through
systems. PET (Positron-emission tomography) makes use of radioactive isotopes to
scan areas of the body
PET scan of a normal
brain
PET scan of an
Alzheimer’s patient
CHEMICAL BONDS - atoms held together by bonds form molecules. Bonding
depends on the number of electrons in the shells of the atom. (The first shell holds 2
electrons, shells after that can hold up to 8 electrons)
IONIC BONDS - an electron is "donated" to another atom
COVALENT BONDS - electrons are shared between atoms
Nonpolar Covalent bonds - electrons shares equally
Polar Covalent bonds - electrons shared unequally, resulting in a partial
negative/positive charge
DOUBLE BONDS occur when two electrons are shared, as in O2 (oxygen)
What about Water?
Water's properties make it unique and essential
for life processes (and all life on earth)
Water is formed by polar covalent bonds, which
determine the arrangement of water molecules.
HYDROGEN BONDS - weak bonds that form
between molecules, the positive hydrogen atom
is attracted to the negatively charged atom on
water, which creates COHESION.
COHESION results in SURFACE TENSION, this property of water is what allows
insects and other small animals to walk across water.
Water Properties





Cohesion & adhesion allow water to be pulled up from the roots of plants all
the way to its leaves (CAPILLARY ACTION)
Water insulates the earth, it has the ability to store a great amount of heat
Water's solid state (ice) is less dense than its liquid state. Ice floats
Water is an important solvent. Hydrophilic substances (sugars) dissolve
readily in water, hydrophobic substances do not (oil)
Note on the image how the water molecules arrange themselves