Atomic Number, Mass Number,
and Isotopes
MS. KNICK
CHEM 1A
HAHS
Subatomic Particles
 There are three subatomic particles:
 1. Electrons (negatively charged)
 2. Protons (positively charged)
 3. Neutrons (neutral = no charge)
Locations of the Subatomic Particles
 Neutrons and protons
are located in the
nucleus
 Electrons are located
in orbitals surrounding
the nucleus (electron
cloud)
How many protons, electrons, and neutrons?
 Look at your periodic table.
Also called the
mass number
Atomic Number
 Is specific for each element (each





element has its own atomic
number)
Whole number at the top of the
element tile
Periodic table is arranged
according to increasing atomic
number
Never changes for a particular atom
The atomic number represents the
number of protons.
It also represents the number of
electrons because an atom is
neutral
The atomic
number of carbon
is 6. Carbon has 6
protons and 6
electrons.
Check your understanding!
 How many protons does titanium have? How many
electrons?
 How many protons does tungsten have? How many
electrons?
 How many protons does radon have? How many
electrons?
Atomic Mass
 Also called the mass number
 Decimal number at the bottom of the tile
 Units are atomic mass units (abbreviated as amu)
 Represents the total number of protons and neutrons in the
atom.
 You may round it to the nearest whole number
Carbon’s atomic mass is
12 amu. It has a total of
12 protons and
neutrons.
To determine the number of neutrons
 Subtract!
 Number of neutrons = atomic mass – atomic number
9–4=
5 neutrons
Check your understanding!
 How many neutrons does platinum have?
 How many neutrons does manganese have?
 How many neutrons does mercury have?
Protons, Electrons, and Neutrons
 Potassium?
 Protons= ______ Electrons = ______ Neutrons=_______
 Nickel?
 Protons= ______ Electrons = ______ Neutrons=_______
 Copper?
 Protons= ______ Electrons = ______ Neutrons=_______
Ions
 An atom with a charge.
 Two types:
 Cation = positively charged (Example: Mg2+)
 Anion = negatively charged (Example: F-1)
Ions and Electrons
 The charge of an atom affects the number of
electrons.
 Cations are positive. They are loosing electrons and
thereby are becoming MORE POSITIVE.
 Anions are negative. They are gaining electrons and
thereby are becoming MORE NEGATIVE.
Example
 How many protons, electrons, and neutrons?

O2-

Al3+

F-

Mg2+
Isotopes
 Isotopes are atoms that have the same number of
protons but a different number of neutrons.
 As a result, isotopes of the same element have a
different atomic mass.
 This is why the atomic mass, is a decimal number.
The atomic mass is an average of all isotopes of a
particular element.
Isotopes of Hydrogen
Formula for Average Atomic Mass
Example:
 Silicon has three isotopes. The data is below. What is
the average atomic mass?
Mass
Abundance
Isotope 1
27.98 amu
92.21%
Isotope 2
28.98 amu
4.70%
Isotope 3
29.97amu
3.09%
Color Code the Periodic Table! Please make it
neat and clear to read!
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
K.
L.
Color the square for Hydrogen pink.
Lightly color all metals yellow.
Place black dots in the squares of all alkali metals.
Draw a horizontal line across each box in the group of alkaline earth
metals.
Draw a diagonal line across each box of all transition metals.
Color the metalloids purple.
Color the nonmetals orange.
Draw small brown circles in each box of the halogens.
Draw checkerboard lines through all the boxes of the noble gases.
Color all the lanthanides red.
Color all the actinides green.
When you are finished, make a NEAT key underneath the title of
your periodic table.