Chemistry 101
What is Chemistry?
The study of MATTER and
changes in MATTER
What is Matter?
The smallest, most basic unit of
“stuff” in the universe.
It has mass and volume.
Why does Matter matter?
• Matter makes up Atoms
• Atoms make up Elements
• Elements can combine to
make Molecules
• Elements and Molecules
make up Chemicals
• Chemicals make up
everything around us!
Sounds simple enough, right?
Let’s make things a little more
complicated…
Atoms
• Are made up of matter
• The matter is organized into
three types of particles
• Protons
• Electrons
• Neutrons
Atomic Particles
• Protons are positive
• Neutrons are neutral
• Electrons are negative
 Are found in the
atom’s nucleus
 Are found in the
electron cloud around
the nucleus
electron
neutron
proton
Electronic Rain?
• Electron clouds are not actually little
clouds of electrons around the nucleus.
• An electron cloud is a drawing that
represents the likelihood that an electron
will be found in a general area around the
nucleus.
• Electrons are SO fast that we can never
actually tell where one is.
Well, if we can’t see them….
• How do we know where they are?
• In 1911, Dr. Ernest Rutherford performed
an experiment.
• He shot a beam of high energy alpha
particles at a very thin piece of gold foil.
• He detected where the particles hit with a
detecting screen made with zinc sulfide.
© Murray Robertson 2001 - 2005
RSC chemsoc timeline, http://www.rsc.org/chemsoc/timeline//pages/1911.html
The Gold Foil Experiment
• Rutherford found out that most of the
particles went straight through, but about
1 in 8000 bounced off.
• He determined that most of the atom was
made up of 'empty space'.
• Before this, everyone figured atoms were
solid mixes of all the different particles.
• This is how we know the weight of an atom
is all in a small nucleus in the center.
Atomic Notation
• X is the chemical symbol
• A is the atomic number
– A = # of protons
• M is the atomic mass
– M = # protons + neutrons
Isotopes
• Elements are determined by
their number of protons. This
number does not change.
• Elements with a different
number of neutrons than
protons are called isotopes.
• Some elements have many
isotopes, some have none.
• Isotopes are identified by
atomic mass.
Ions
• Elements are determined by their number
of protons. This number does not change.
• Elements with a different number of
electrons than protons are called ions.
• If an element loses an electron, it becomes
more positive and is called a cation.
• If an element gains an electron, it becomes
more negative and is called an anion.
Ion Notation
• Ions are notated by
placing a positive or
negative sign after the
chemical symbol.
• If there is more than
one charge, the
number is placed
before the charge.
Back to our first definition
• Chemistry is the study of matter AND
changes in matter.
• What kind of changes are we talking
about?
Physical v. Chemical Changes
• Physical changes do
not actually change
matter, they just
reshape it.
– melting
– freezing
– boiling
– condensing
– sublimating*
– crushing
– bending
• Chemical changes
change the
arrangement of
matter at the
molecular level.
– burning
– rusting
– chemical reactions!
* we’ll get to this word, don’t worry
State changes
• Some physical changes are called “state
changes”.
• These occur when matter shifts between a
solid, liquid, or gas state.
solid
gas
melting
condensing
solid
liquid
liquid
sublimating
boiling
freezing
gas
gas
solid
Congratulations!
You are now on your way to
becoming a chemist.