ATOMIC STRUCTURE WORKSHEET
NAME __________________________________
Atoms are composed of three sub-atomic particles: the proton, the neutron, and the electron. The proton
and the neutron are found in the nucleus. Electrons are found in a cloud surrounding the nucleus.
The atomic number of an element is equal to the number of protons in that element. If the atom is neutral,
the number of electrons (-) is equal to the number of protons (+).
If the atom carries a charge, it is referred to as an ion. The charge on an ion indicates an imbalance
between protons and electrons. If the ion has a positive charge, there are more protons than electrons. To
find the number of electrons, you must subtract the charge from the atomic number. If the ion has a
negative charge, there are more electrons than protons. To find the number of electrons, you must add the
charge to the atomic number.
The mass number is a whole number equal to the number of protons plus neutrons. This is because we say
that protons and neutrons each have a mass of 1 amu (standardized from Carbon-12). This number is not on
the periodic table. The atomic mass is the weighted average atomic mass of all the naturally occurring
isotopes of an element. This number is located on the periodic table and is usually a decimal.
(Remember, an isotope is an atom of the same element with a different number of neutrons; an ion is an
atom of the same element with a different number of electrons.)
X= element
Mass number
A= mass number (# of protons + # of neutrons)
Z= atomic number (# of protons)
A - Z = # of neutrons
Isotopic symbol is in this form:
Atomic number
Charge
Element symbol
A
X
Or, you might see: X – A
Example: Aluminum - 26
Z
Complete the chart.
Element/Ion
1
H
1
1 1+
H
1
14 3N
7
41
Ca
20
108
Ag
47
108 1+
Ag
47
Atomic
Number
Atomic Mass
Mass
Number
Protons
Neutrons
Electrons
Define the following:
Atomic Number _______________________________________________________________________
Mass Number _________________________________________________________________________
Atomic Mass _________________________________________________________________________
Isotope _______________________________________________________________________________
Ion ___________________________________________________________________________________
Isotope Name
Isotope
Symbol
Protons
Number of…
Neutrons
Electrons
Atomic
Number
Mass
Number
16
34
20
40
Argon-40
Argon-38
Bismuth-209
57
26
Fe
209
82
Pb
28
37
30
34
28
48
37
Aluminum-27
Manganese-55
11
12
SUMMARIZE:
How do you find the number of protons for any atom?
How do you find the number of neutrons for any atom?
How do you find the number of electrons for any atom?
11