Atoms are the basic building blocks of matter and are composed of protons, neutrons, and electrons. Protons and neutrons are located in the nucleus at the center of the atom, while electrons occupy energy levels that orbit around the nucleus. The number of protons determines the element and is referred to as the atomic number. Atoms are electrically neutral overall, with the same number of protons and electrons, while neutrons have no charge. The mass number accounts for the total number of protons and neutrons in the atomic nucleus. Electrons can only occupy certain energy levels, with the first level holding up to two electrons and successive levels increasing in capacity.

1. Atomic Structure Notes
Atoms:
- Smallest particle of an element that
has all the properties of that element.
- -Atoms are the basic building blocks
of matter that make up everyday
objects.
-2 main parts of an atom:
Nucleus-99.9% of the atom’s mass
Electron cloud or energy rings
-Atoms are made of subatomic particles:
protons, neutrons, & electrons

2. Atoms are composed of three primary particles:
protons, neutrons, and electrons
Particle Symbol Location
Electrical
Charge
Relative
Mass
(amu)
How do you
find out
how many?
Electron
Proton
Neutron

3. Particle Symbol Location
Electrical
Charge
Relative
Mass
(amu)
How do you
find out
how many?
Electron
Proton
Neutron
Atoms are composed of three primary particles:
protons, neutrons, and electrons
e-
Orbits
nucleus in
energy
levels
-1
(negative)
1/1840
Atoms are
neutral and
therefore
have the
same # of
electrons as
protons
P+
Inside
Nucleus
+1
(positive)
1
Atomic # (#
of protons
in an atom’s
nucleus),
Element
specific
no Inside
Nucleus
0
(no charge/
neutral)
1
Mass #
minus
atomic #

4. Electron Energy Levels
Energy Level How many electrons it holds up to
1 2
2 8
3 18
There is a unique number of
electrons that can fit in each
electron level.

5. Determining Atomic Structure Using the Periodic Table
Atomic Number
Atomic Mass #: The
weighted average mass of all the
isotopes (different versions) of an
atom of a specific element;
measured in atomic mass units,
amu.
Chemical Symbol
Element Name
B
5
Boron
10.81
Mass #: Atomic Mass Number
rounded to the nearest whole number.

6. ATOMIC STRUCTURE DIAGRAMS
Step 1: Complete the squares for
each element by adding the atomic
number, name and atomic mass.
- Write the atomic number at the top of
the square.
- Write the element’s name under the
symbol.
- Write the atomic mass at the bottom of
the square.
Step 2: Determine the number of
protons, neutrons, and electrons in
each element.
Step 3: Create an atomic structure
diagram for each element.
Step 4: Draw the Bonding Structure
for each element.
5
B
Boron
10.81
P = 5
N = 6
E = 5
Atomic Structure:
Bonding Structure: B
5 P+
6 no