6.1: Atoms, Elements, and
Chemistry is the study of matter.
Matter is anything that has mass and takes up
Atoms are the building blocks of matter.
THE STRUCTURE OF ATOMS:
Billions of atoms could fit on the head of a pin!
Atoms are made up of even smaller particles –
The Structure of Atoms:
Nucleus – the center of an atom
Within this nucleus are protons and neutrons.
Neutrons – particles that have no charge
Protons – particles with a positive charge
Electrons – negatively charged particles located
outside the nucleus.
Constantly move around the nucleus in energy levels.
Are attracted to the protons
Atoms contain an equal number of protons and
neutrons so the overall charge of an atom is neutral.
An element is a pure substance that cannot
be broken down into other substances by
chemical or physical means.
Are made of only one type of atom.
Information collected about each element
has been organized into a chart called the
periodic table of elements.
Organized into horizontal rows called
And vertical columns called groups.
Is an extremely important element in biology and
chemistry because nearly all of the molecules of living
things contain carbon.
Isotopes – atoms of the same element that have
different numbers of neutrons.
Mass number (A) = number of
protons and neutrons.
Atomic number (Z)= number of
protons in the nucleus.
How many neutrons in Carbon 14?
Neutrons have no charge so a change
In their number has no effect on charge.
Carbon 14 is a radioactive isotope.
A change in the number of neutrons CAN change the
stability of the nucleus causing it to decay (or break
When a nucleus decays, it gives off radiation that can
be detected and used for many applications.
Isotopes that give off radiation are called radioactive
Carbon 14 is a radioactive isotope found in all
Half life – the amount of time it takes for half of the
carbon 14 to decay.
Elements can combine to form more complex
Compounds are pure substances formed when two or
more different elements combine.
6.2: Chemical Reactions
Chemical reactions allow living things to grow,
develop, reproduce, and adapt.
The human body is a 24 hour reaction factory!
A chemical reaction is the process by which atoms or
groups of atoms in substances are reorganized into
different substances. Chemical bonds are broken
and/or formed during chemical reactions.
Rust forms when oxygen in the air
reacts with iron:
A light stick consists of a
glass vial, containing one
chemical solution, housed
inside a larger plastic vial,
containing another solution.
When you bend the plastic vial,
the glass vial breaks, the two
solutions flow together, and the
resulting chemical reaction
causes a fluorescent dye to emit
It’s important to know that substances can undergo
changes that do not involve chemical reactions.
Water, for example, can undergo physical changes:
Reactants and Products
A chemical equation shows the reactants on the right
side of an arrow, and the products on the left.
Reactants – the starting substances of a chemical
Products – The substances formed during the
C6H12O6 + O2 6CO2 + 6H2O
Glucose and oxygen react to form carbon dioxide and
water. (This is cellular respiration.)
In chemical reactions, matter cannot be created not
destroyed. All chemical equations must show a
balance of mass.
Section 6.3: Water and Solutions
Properties of water (H2O):
Water is a polar molecule – it has an unequal
distribution of charges.
Hydrogen bonds – a weak attraction involving a
hydrogen atom and an oxygen atom. This is a van der
Waals force which is responsible for keeping water
Water has surface tension due to van der Waals forces.
Water striders can stand on water.
Water droplets can form.
A mixture is a combination of two or more substances
in which each substance retains its individual
characteristics and properties.
Homogenous mixture – uniform composition
Heterogenous mixture – components remain distinct,
do not dissolve
A solution is a homogenous mixture. Two
components of a solution are:
Solvent – substance in which another substance is
Solute – the substance that is dissolved in the solvent.
Acids and Bases:
Acids are substances that release hydrogen ions
when dissolved in water.
The more hydrogen ions a substance releases, the
more acidic the solution becomes.
Substances that release hydroxide ions (OH-)
when dissolved in water are called bases.
NaOH is a common base that breaks apart in water to
release Na+ and OH- ions. The more OH- ions present,
the more basic a solution is.
The amount of hydrogen ions
or hydroxide ions in a
solution determines the
strength of an acid or a base.
We can easily measure the pH
of a solution using a pH
meter or pH paper.
See the pH scale to the right.
Water is neutral (pH 7)
Acids have a pH lower than
that of water.
Bases have a pH higher than
that of water.
What’s a buffer?
1. List the atoms involved in photosynthesis.
2. List the molecules involved in photosynthesis.
3. List the compounds involved in photosynthesis.
6CO2 6H2O energy C6H12O6 6O2
Carbohydrates + oxygen = carbon dioxide + water +
Chemical Equation for Cellular
C6H12O 6O2 6H2 energ