The nucleus is at the center of the atom. Positively charged particles called protons and particles with no charge called neutrons are located in the nucleus. Electrons with negative charges are located outside the nucleus. Atoms contain an equal amount of protons and electrons and have a total charge of zero.
An element is a substance that cannot be broken
down by physical or chemical means.
Elements are organized in a periodic table based
on the arrangement of their electrons.
The four most common elements in living things
are Carbon, Hydrogen, Oxygen and Nitrogen.
Isotopes, Radioactive Isotopes Atoms of the same element that have different numbers of neutrons are called isotopes. If an atom is unstable , the nucleus can decay and give off radiation – these are called radioactive isotopes. Carbon-14 is a radioactive isotope that is found in all living things. Scientists can determine how old an object is by determining how much Carbon 14 is in the object.
A compound is a pure substance formed
when two or more different elements
combine. Compounds can not be broken
down by physical means.
Water is the compound H 2 O. Table salt is the compound NaCl. Hydrocarbons are compounds made of Carbon and Hydrogen. Methane CH 4 is a hydrocarbon.
Chemical bonds hold substances together
by either sharing or donating electrons
Covalent bonds form when electrons are
shared between atoms.
A molecule is a compound held together by
Sometimes atoms will form more than one
covalent bond between their electrons,
double or triple bonds.
Ions form when atoms gain or lose electrons.
Some ions are positively charged Na + and some
ions are negatively charged Cl -
An ionic bond forms through the electrical
force between oppositely charged ions.
Substances that form from ionic bonds are
called ionic compounds.
A chemical reaction is the process by which atoms or
groups of atoms in substances are reorganized into
A chemical equation shows the reactants and the
In a balanced equations , mass is
conserved and coefficients show
that the number of atoms of each
element is the same before and
after the reaction.
Energy of Reactions
Activation energy is the minimum amount
of energy need for reactants to form
products in a chemical reaction.
Exothermic Reaction Endothermic Reaction
A catalyst is a substance that lowers the
activation energy to start a reaction.
Enzymes are biological catalysts that
speed up the rate of chemical reactions in
Most enzymes are proteins. Temperature and pH changes can alter the shape of an enzyme and lower its activity.
S ubstrate s are the substances acted
on by enzymes. They bind at the active
The “lock and key” model
Water is a Polar Molecule
In water, electrons spend more time near
the oxygen nucleus than the hydrogen
Molecules that have an unequal distribution of charges are called polar molecules . In water, the electrical attraction between the negative oxygen side of one water molecule and the positive side of the other water molecule form hydrogen bonds. Section 6-3 Water and Solutions
Solutions and Suspensions
A solution is a homogenous mixture
because it has a uniform composition.
A suspension is a heterogenous mixture
because it does not have a uniform
composition and the particles settle out.
A colloid is also a heterogenous mixture
because it does not have a uniform
composition but in a colloid the particles do not settle out.
Section 6-3 Water and Solutions
Water – solvent of life
The polarity of water makes it
A solution is a mixture of
substances that is the same
The solvent is the substance
in greater quantity in a
The solute is the substance
that dissolves in the solvent.
Acids and Bases
Substances that release Hydrogen (H + ) ions
when they are dissolved in water are called acids.
Substances that release Hydroxide (OH - )
ions when they are dissolved in water are
The amount of H + or OH - ions in a solution
determines the strength of an acid or base.
pH measures the concentration of H+
ions in a solution.
Acidic solutions have pHs lower than 7
Basic solutions have pHs higher than 7
A pH of 7 is neutral (distilled water)
pH and Buffers
A buffer is a mixture that can react with
acids or bases to keep the pH in a particular
The Building Blocks of Life
Organic chemistry is the study of organic
compounds containing carbon.
Carbon has four outer electrons and so can
form four covalent bonds with other atoms.
Macromolecules are large molecules made by joining smaller organic molecules together.
Polymers are made of repeating units of monomers.
Section 6-4 The Building Blocks of Life Monomer Polymers
Lipids provide structure
and support, Nucleic
acids store and
Proteins provide a wide
variety of functions.
The four major categories of macromolecules are Carbohydrates, Lipids, Proteins and Nucleic Acids.
Tree of Life Macromolecules
Carbohydrates contain Carbon, Hydrogen
Simple sugars like Glucose are called monosaccharides . Two simple sugars joined together are called a disaccharide. Ex: Sucrose. Many sugars covalently connected in a chain are called a polysaccharide . Polysaccharides : Glycogen Cellulose Chitin
Lipids are made mostly of Carbon and
Hydrogen. The monomers are called fatty acids.
Lipids are non-polar molecules like fats and
Saturated fatty acids have
no double bonds in the chain.
Unsaturated fatty acids
have one or more
double bonds in the chain .
Section 6-4 The Building Blocks of Life
Phospholipids and Steroids
A special lipid called a phospholipid is
important for cell membranes.
Other lipids are called steroids
and include cholesterol and
hormones like estrogen and
Proteins are chains of monomers called
amino acids held together by peptide
Proteins contain Carbon, Nitrogen,
Hydrogen, Oxygen and sometimes Sulfur.
There are 20 different amino acids.
The many shapes formed by proteins allow
proteins to provide functions ranging from
support and transport to communications ,
speeding up reactions and control of cell
Proteins can form a variety of 3-dimensional structures.