Chemistry of Life

Physiological processes based upon proprieties and
interactions of atoms, ions, and molecules.

Water is the major constituent (compound) of the body (6575% of body weight)
 2/3 water intracellular;
 1/3 extra cellular (lymph, blood plasma,
interstitial fluid, urine, saliva, etc…)
ELEMENTS AND ATOMS
ELEMENTS: Living and non-living things are composed of
elements which cannot be broken down further into simpler
substances. Every element has a name, a chemical symbol,
and an atomic number. 99% of the body is composed of 6
elements: Carbon, oxygen, hydrogen, nitrogen, calcium and
phosphorus
ATOMS: General term of a structure composed of
 Neutrons
 Protons
 Electrons

The number of subatomic units vary from element to
element - Different protons = different elements
Definition: The smallest unit of an element that still retains
the chemical and physical proprieties of the element
ATOMS
Nucleus
Protons
 Neutrons

One atomic mass unit – Positive charge
One atomic mass unit – Neutral charge
Outer Energy Shells –

Electrons
Almost no mass - Negative charge
Arranged in shells
1st shell: 2 electrons
2nd Shell: 8 electrons
3rd shell: 1 electrons (happy
with 8)
Valance electrons: electron
in the outermost shell,
participate in chemical
reactions
Atomic Number: Number of protons of an Atom. Determines
what kind of element it is
Ex. Carbon 6 protons, Oxygen 8 protons
Atomic Weight = number of protons + number of neutrons
(Mass)
(electrons are so light they don’t count)
Isotopes - different number of neutrons in an element.
 Unstable – commonly radioactive elements

Atomic Number is the same – atomic mass is different
Ions – charged atoms

Anions:
Negatively charged atoms
More electrons than protons

Cations:
Positively charged atoms
More protons than electrons
Molecules and Compounds
Atoms bond with each other to form a chemical unit
 Simple molecules – same atoms
 Compound molecules – different atoms
Molecular formula – indicates proportion, number and types
of atoms in a molecule
Octet Rule: Atoms react to produce 8 electrons in outer shells
(hydrogen and helium are exceptions because
they only have enough electrons to fill first shell,
maximum capacity 2)
Ionic Bonds – When one or more valence electrons are
transferred from one atoms to another producing
ions of opposite charge
 The atoms losing electrons became
positively charged
 The atoms gaining electrons became
negatively charged
 Opposite charges bring atoms together and
create a bond
Ionic bonds are weaker than covalent bonds
(dissociate easily)
Covalent Bonds: Atoms form a molecule by sharing a pair
of valence electrons.
Covalent bond –
Polar – unequal share of electrons
 Apolar – equal share of electrons

POLAR
APOLAR
Hydrogen Bonds: Intermolecular bonds
 When a partially positive hydrogen atom is attracted to a
partially negative atom
in another molecule.
 Attraction between the
positive and the negative
portion of a Polar molecule
 Important organic bonds,
relatively weak
 Example: water
Chemical Reactions
Anabolic Reaction – synthesis reaction
 Reactions that create a molecule
 Requires Energy
 2N + 6H  2NH3
Catabolic Reactions – break down reaction
 Reactions that break molecules down
 Liberate Energy
o Excess energy may be
stored in a molecule ATP
 CH4  C + 2H2
Exchange Reactions: - Molecules exchange atoms
 NaOH + HCL  NaCl + H2O
Properties of Water
 Liquid at room temperature
(rather than a gas)
 Universal solvent for
polar molecules
 Medium for chemical reactions
 Involved in many chemical reactions
 Excellent transport medium
 Evenly distributes dissolved substances
 Resistant to temperature changes - Stabilizes body
temperature
 Frozen water is less dense than liquid. (Ice floats on water)
 Water is the most abundant compound in the body
***
BUFFERS
A system of molecules and ions that act to prevent changes in
H+ concentration solution
Blood Buffer – Blood pH ranges from 7.35 – 7.45
 Below 7.35 = acidosis
 Above 7.45 = acidosis
Bicarbonate ions (HCO3-): base that buffers acid
metabolic wastes
 Carbonic Acid (H2CO3): Acid that buffers loss of body
acids
HCO3- + H+ = H2CO3

ACIDS / BASES / pH Scale
ACIDS – Hydrogen Donators –
Molecules that release or donate hydrogen ions (protons) to a
substance
 Acid solutions have much H+, low pH

BASES – Hydrogen acceptors Molecules that take up
hydrogen ions (protons) or dissociate in water to release OHions.
 Basic solutions have few H+ and high pH

Neutral solutions: pH7 – pure water – contain equal amounts
of H+ and OH-
Living organisms maintain pH homeostasis of body fluids