http://www.biology.arizona.edu/biochemistry/tutorials/chemistry/pag
e2.html
Chemistry: Atoms and Their
Interactions
Miss Kim Jensen
Biology
2002-2003
Glencoe – biology
dynamics of life 2002
McGraw/Hill
What is an element?
 An element is something that can’t be broken down
into simpler chemical substances.
 There are 90 naturally occurring elements on earth.
 Where did the rest come from?
 How many are essential to living organisms?
 25
 Only four elements make up more than 96 percent
of the mass of a human. Which ones are they?
 Carbon C , Nitrogen (N) Hydrogen (H) and Oxygen (O)
What is a trace element?
 These are elements such as iron and magnesium that
are present in living things in very small amounts.
 Although they are in small amounts, they play
important roles in maintaining healthy cells in all
organisms.
 For example, Magnesium aids in the absorption of
calcium.
 So when you look for Calcium supplements, instead
of looking at the calcium amount, look at the
magnesium amount.
 Did you know that Tums only gives you a 1% Ca
absorption.
Other examples of trace
elements.
Mammals use iodine (I) to produce
biochemical's for growth and development.
Plants use MG to form chlorophyll (which
captures light energy for making sugar)
Fluorine binds to the surface of teeth
making them resistant to decay.
What are elements made up of?
 Atoms.
Atoms are the basic building blocks of all
matter.
The atom is a smaller particle of that
element that holds all of the characteristics
of that element.
Atoms consist of . . . . . . . . .
 A nucleus containing protons (positively charge)
and neutrons (no charge).
 The positive charged nucleus is surrounded by a
cloud of rapidly moving, negatively charged
electrons.
 Electrons travel around the nucleus in regions
known as energy levels.
 The first energy level is closest to the nucleus and
is so small that it can only fit 2 electrons.
 The second energy level can hold 8 e The third can hold 18 e-
O has 8 e-. So how many
electrons are in each level?
2 e- in Energy level 1
6e- in Energy level 2
Number of protons (p+) = Atomic number
Number of p+ = number of eNumber of p+ plus number of n = atomic
mass or atomic weight.
The elements on the periodic table are in
order of increasing atomic number.
Can you figure out which
elements belong to the following
configurations.
G
V
L
O
N
IrF
iexIA
ol
toyIA
u
hngA
po
ieIr
unA
i
m
n
e
You try it.
 How many p+,n, e- in .. . . . . . . .
 Look at your periodic table on A9 (Glencoe
book).
 What are isotopes?
 Atoms of an element that contain a different
number of neutrons in the nucleus.
 These are referred to by the atomic mass which is
the combined total of protons plus neutrons.
 For example carbon-12. Has 6 p+ and 6 n.
 How many neutrons do carbon-13 have? How
many do Carbon-14 have?
Why are isotopes useful?
 The nuclei of some isotopes are unstable and will
break apart giving off radiation.
 These isotopes are radioactive.
 Radioactive iodine is absorbed by the thyroid
gland, allowing doctors and scientists to scan the
thyroid to measure how well it is working.
 Cancer patients can be treated with radioactive
isotope of cobalt (Co) which is deadly to rapidly
growing cells.
What is a compound?
A compound is a substance composed of
atoms of two or more different elements
that are chemically combined.
For example, water is a compound of 2
hydrogen's and 1 oxygen.
How do atoms become stable?
Atoms become stable by bonding to other
atoms through covalent or ionic bonds.
What are the different types of bonds?
 Covalent, Ionic, Hydrogen and others.
Most matter is in the form of compounds
but they must combine in a way that will
make them stable and happy.
Isn’t that what we all want?
What is a covalent bond?
 Covalent bonds form when two atoms share
electrons. Why do they do this?
 Because they want to be stable and sharing
electrons will fill their outer energy level.
 What is a molecule?
 A group of atoms held together by covalent bonds.
(like water)
Insulin is a complicated molecule called a protein.
We will later consider simpler ways to consider the
complicated molecules of life.
What is an ionic bond?
 Sometimes, instead of sharing electrons, it is
easier for atoms to gain or loose electrons in their
outer energy levels (or shells).
 By doing this they become charged and can
attract atoms of the opposite charge.
 Loosing an e- makes an atom + charged.
 Gaining an electron makes an atom – charged.
 The attractive force between two ions of opposite
charge is the ionic bond. And these are called
ionic compounds instead of molecules.
 Ionic bonds generally form between metals and
non-metals (see periodic table to know which is
For example Na (sodium) can donate an electron to
Cl (chlorine) generating Na+ and Cl-. The ion pair is
held together by strong electrostatic attractions.
Are ionic compounds important?
Ionic compounds are less abundant in
living things than covalent molecules, but
are still very important in biological
process.
Example, potassium ions are used for
transmitting nerve impulses.
Calcium ions are necessary for muscles to
contract.
Non-covalent bonds and other
weak forces -Linus Pauling, 1946
 Chemical reactivity of molecules- tendency to break
and form chemical bonds.
 Biology of molecules- size and shape of molecules, an
the nature of weak interactions with other molecules.
 Non-covalent bonds and other weak forces are
important in biological structures.
 Electrostatic bonds(ionic)-result from the electrostatic
attraction between two ionized groups of opposite
charge, such as carboxyl (-COO-) and amino (-NH3+).
In water, these bonds are very weak.
 N-H ----- O=C- -O-H----- O=C-
Van Der Waals forces
 Van Der Waals bonds-are short range attractive forces
between chemical groups in contact. Caused by slight
charge displacements.
 Hydrogen bonds-result from electrostatic attraction
between an electronegative atom (O or N) and a hydrogen
atom that is bonded covalently to a second electronegative
atom.
 Hydrophobic attractions-cause non-polar groups such as
hydrocarbon chains to associate with each other in an
aqueous environment.
 Multiple weak bonds or forces can cause strong
interactions
What is a chemical reaction?
 When chemical reactions occur, bonds are
formed or broken, causing the substance to
recombine as a different molecule.
 Chemical reactions occur inside cells of
organisms and are referred to as the organism’s
metabolism.
 These reactions break down and build molecules
important for organisms to function properly.
Writing and balancing equations
Reactant are what you start with (flower,
water etc.)
Products are what you end up with (the
cake).
The word equation:
– Flower + water + stuff = cake.
Reactants must = the products for the
equation to balance.
What is the differences between
mixtures and solutions?
 Components of mixtures retain their properties –
components of solutions do not.
 Mixture is a combination of substances in which
the individual components retain their own
properties.
– (like making pizza, or a combination of sand and
sugar)
 A solution is a mixture in which one or more
substances (solutes) are distributed evenly in
another substance (solvent)
– Sugar molecules (solute) dissolve in water (solvent)
when you make
Why is this important in
biology?
The pancreas and other organs will
produce substances (like insulin) to keep
the amount of sugar dissolved in the blood
within a specific range.
Acids and bases
 Acid is a substance
that forms hydrogen
ions (H+) in water
 Any substance that
forms hydroxide ions
(OH-) in water
 (PH is 0 to 7)
 (ph is 7 to 14)
Acids and bases are important to living systems but
can also be dangerous. For example, orange juice is
an acid that can corrode teeth. Some organisms and
plants prefer acidic environments.