Introduction to Chemistry Notes
Matter- anything that has mass and takes up
space
Atom—a small particle that makes up most
types of matter
Law of conservation of matter—Matter is
neither created nor destroyed; it only
changes in form.
Avogadro’s Number—It takes 6.022 x 1023
atoms to make up the number of grams in
the atom’s atomic mass.
Parts of an Atom
Electrons (e-)—negatively charged particles that
surround an atom’s nucleus. They have a net
charge of -1 and virtually no atomic mass.
Protons (p+)—positively charged particles in
the nucleus; they have charge of +1 and an
atomic mass of 1 amu (atomic mass unit).
Neutrons (n0)—neutrally charged particles in
the nucleus of an atom; they have no charge (+0)
(neutral) and have an atomic mass of 1 amu.
How to use Atomic Structure
Atomic Number—the number of protons in an
atom; this number determines what kind of atom
it is
Ex. Atomic number of 3 is lithium
**In a neutral atom, there are an equal number
of protons and electrons**
How to determine atomic mass: The atomic
mass of an atom can be found by adding the # of
protons + the # of neutrons in the nucleus
For example:
Carbon: 6 protons + 6 neutrons = 12 amu
Technetium: 43 protons + 55 neutrons = 98 amu
The Rules!
To find the number of neutrons:
Atomic Mass - # of protons = # of neutrons
*** The # of Electrons = # of protons***
*** The atomic # = the # of protons***
Isotope—A form of an element with the same
number of protons, but a different number of
neutrons and therefore a different atomic mass.
Ex. Carbon 14 has 8 neutrons and Carbon 12
has 6 neutrons
Element—matter that is made up of only one
kind of atom. There are 118 known elements.
Substance-matter that has the same composition
and properties throughout
Compound—a substance whose smallest unit is
made up of atoms of more than one element
bonded together.
History of Atomic Structure
Democritus—an ancient Greek that believed
that matter was made up of tiny bits of stuff that
could not be broken down any smaller. He
called these things “atoms”.
Lavoisier—realized that when you burn wood
that matter is conserved—ash, water, carbon
dioxide and other gases are produced
John Dalton—in the early 1800’s Dalton came
up with atomic theory
J.J. Thompson—discovered that you could
deflect an electric ray with a magnet; he
discovered the electron.