Introduction to Chemistry
Objectives…
• Define chemical element, atom, ion,
molecule and compound
• Explain how chemical bonds form
• Describe what happens in a chemical
reaction and explain why it is important
to the human body
Chemical Element
• Substances that cannot be broken down
by normal chemical means
• ~112 known chemical elements
• Each is designated by a chemical
symbol
• 26 elements are found in the human
body
• 96% of the body’s mass is made from
Carbon, Hydrogen, Oxygen and
Nitrogen
• 3.8% is from Calcium, phosphorus,
potassium, sulfur, sodium, chlorine,
magnesium and iorn
Trace Elements
• The remaining 0.2% of the body’s mass
is made of these 14 elements:
– Al, B, Cr, Co, Cu, F, I, Mn, Mo, Se, Si, Sn, V
and Zn
– Even though they are present in REALLY
small amounts, they are still essential to
maintain homeostasis!
Atoms
• Each element is made up of a single
type of atom
• The are the smallest units of matter
that retain the properties of the
element
Subatomic Particles
• Protons (+) and Neutrons (0) are
located in the nucleus of the atom
• Electrons (-) move around in the space
surrounding the nucleus
• The number of protons in an atom
equals the number of electrons, giving
the atom a net charge of zero
• Atomic Number – the number of
protons
• Atomic Mass – the number of protons
plus the number of neutrons
• Electron Shells – the area around a
nucleus where you are most likely to
find an electron
Ions
• If an atom gives up or gains an electron
it becomes an ion.
• An ion is an atom that has a positive or
negative charge due to unequal
numbers of protons and electrons
• Cation – a positive ion
• Anion – a negative ion
Molecules
• When 2 or more atoms share electrons,
the resulting combination is called a
molecule
• May be 2 or more atoms of the same
element (O2) or of different elements
(H2O).
Molecular Formulas
• A molecular formula indicates the type
of and how many atoms are in a
molecule
– Ex – H2O means 2 hydrogen atoms and 1
oxygen atoms have joined
Compound
• A molecule containing 2 or more atoms
of different elements
Free Radical
• An electrically charged ion or molecule
that has an unpaired electron in its
outermost shell
• A free radical is unstable and
destructive to nearby molecules
• They break apart other molecules in the
body by either giving up their unpaired
electron or by taking an electron from
another molecule.
Free Radicals in your Body…
• Many processes in the body generate
free radicals
• Diseases associated with oxygen
derived free radicals are cancer,
artherosclerosis, Alzheimers,
emphysema, diabetes, cataracts,
macular degeneration, rheumatoid
arthritis, and deterioration associated
with aging.
Antioxidants
• Substances that inactivate oxygen associated
free radicals.
• Consumption of antioxidants is though to
slow the pace of damage caused by free
radicals.
• Dietary sources of antioxidants include
selenium, beta-carotene and vitamins C and
E.
“The antioxidant will protect me…”
Chemical Bonds
• Forces that bind the atoms of molecules
together, resisting their separation.
• Given the right conditions, two or more atoms
can interact (bond) in such a way that a
chemically stable arrangement of 8 valence
(outer) electrons in each atom
• 3 types of bonds:
– Ionic
– Covalent
– Hydrogen (not really a bond if you talk to a
chemist, but a REALLY strong attraction)
Ionic Bonds
• The force of attraction between ions of
opposite charges
• This results from
the transfer of
electrons
• Ionic bonds are found mainly in teeth
and bones, most other ions in the body
are dissolved in fluid.
Electrolytes
• An ionic compound that breaks apart
into cations and anions when dissolved
is called an electrolyte because the
resulting solution can conduct an
electric current
• Critical in controlling water movement,
maintaining acid/base balance and
producing nerve impulses
Covalent Bonds
• Atoms form a molecule by sharing one,
two or three pairs of electrons
• These are the most common chemical
bonds in the body
Polarity
• If the neither atom in a covalent
molecule has a greater attraction for
electrons than the other the bond is
said to be non-polar
• Sometimes the electrons are not shared
equally – one atom attracts the
electrons more strongly than the other.
This results in a polar bond
Polar Covalent Bonds
• The sharing of electrons is unequal
• The side of the molecule that attracts
more electrons will have a partial
negative charge (d-) while the side that
does not have as many electrons will
have a partial positive charge (d+)
• The ENTIRE molecule is still NEUTRAL
Hydrogen Bonds
• A VERY VERY strong interaction between
some polar molecules containing hydrogen
• A hydrogen atom in one molecule with a
partial positive charge attracts a partial
negative atom (F, O or N) from another
molecule.
• About 5% as strong as an actual covalent
bond
Chemical Reactions
• New bonds form and old bond are
broken
Chemical Energy
• Form of potential energy stored in
chemical bonds
• Breaking old bonds requires the input of
energy, forming new bonds releases
energy
Synthesis Reactions
• Smaller molecules
join to make larger
molecules
Decomposition Reaction
• Larger molecules are broken down into
smaller molecules
Exchange Reactions
• Consist of both synthesis and
decomposition
AB + CD  AD + BC
Reversible Reactions
• Reactions that can proceed in either
direction
AB  A + B