Protons, Neutrons, and Electrons Practice Worksheet
Fill in the blanks in the following worksheet. Please keep in mind that the isotope
represented by each space may NOT be the most common isotope or the one closest in
atomic mass to the value on the periodic table.
Atomic
symbol
Atomic
number
Protons
B
Neutrons Electrons
Atomic
mass
6
11
24
31
37
39
29
89
35
43
100
207
Pb
102
89
Mo
70
225
53
81
100
206
159
No
Yb
261
172
106
159
Finding Protons, Neutrons, and Electrons of Elements
One of the things students frequently have problems with is determining how many
protons, neutrons, and electrons an element has, based only on some sparse information
given to you on the periodic table or in a problem. This review will give you everything you
need to figure it out. First, let's examine one of the entries in the periodic table:
This is what the entry for helium is on a normal periodic table. The atomic number is found at
the top, and is equal to the number of protons that an element has. The reason that all atoms
of the element have the same number of protons is that the number of protons determines
what element is present - if there were a different number of protons, you would have a
different element. For neutral atoms, the atomic number is also equal to the number of
electrons present because the number of electrons equals the number of protons in neutral
atoms.
The atomic symbol is different for every element. As you might guess, the atomic symbol and
atomic number are very closely related to one another. After all, any element that has the
atomic number "2" will have the atomic symbol "He". As a result, if you don't know the atomic
number of an element, you can look up the atomic symbol on the periodic table to find it. As a
result, you can determine the number of protons an element has from the atomic symbol if you
have a periodic table handy. The atomic mass is also different for every element, and also for
isotopes of the same element. The atomic mass is equal to the number of protons that an
element has plus the number of neutrons that an element has. This is because protons have a
mass of approximately 1 amu (atomic mass unit) and neutrons have a mass of approximately 1
amu. Electrons don't count in this calculation, because their mass is small enough that it can
usually be ignored.
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Atomic number = number of protons (which, for neutral atoms, is equal to the number
of electrons).
Atomic symbol allows us to find the atomic number because you can just look it up on
the periodic table.
Atomic mass = number of protons + number of neutrons.