Atoms, Ions,
& Isotopes
Oh, My!
Part II
The atoms of different elements contain different
numbers of protons. The number of protons in
the nucleus of an atom is called the atomic
number.
The smallest atom is hydrogen with only one
proton in its nucleus. The largest naturally
occurring atom is uranium with 92 protons in
its nucleus. You can tell what element an
atom is by the number of protons. If you
change the number of protons, then you
change the identity of the element.
The atomic number is the number of protons and
identifies what element an atom is.
However, the number of neutrons can vary in the
same type of element. When atoms of the same
element have a different number of neutrons
they
are called isotopes.
Carbon-12
Carbon-13
Carbon-14
The number of protons and the number of
neutrons added together make up the
mass of the atom. That is called its mass
number.
mass # = protons + neutrons
OR
m# = p + n
Carbon-12
Carbon-14
Carbon-13
Atom Characteristics
• The atomic mass is the mass of the protons
plus the mass of the neutrons.
Atomic mass is recorded in the SI units:
atomic mass units (amu).
Protons and neutrons each are given an amu
of 1.
Electrons have a mass of nearly zero.
5
Decoding Atom Information
from the Periodic Table
Atomic
Number
6
C
Carbon
Atomic
Mass
12.0
Atom’s
Symbol
Atom’s
Name
6
Decoding Atom Information
from the Periodic Table
Atomic number
# of protons = # of
electrons
6
C
Carbon
Atomic mass = # of
protons plus the # of
neutrons
12.0
7
How can I ever
figure out the
number of
protons,
electrons, and
neutrons in a
neutral atom?!
HELP!!!!!
8
APE MAN to the rescue!
9
A = P = E
t
o
m
i
c
N
u
m
b
e
r
R
o
t
o
n
s
l
e
c
t
r
o
n
s
(if neutral)
M - A = N
a
s
s
t
o
m
i
c
N
u
m
b
e
r
e
u
t
r
o
n
s
10
Using APE MAN
Let’s say you’re trying to find the number of protons,
electrons, and neutrons of a neutral atom of Sodium (Na).
Fill out the information you have:
Atomic number is 11. Mass is 23.
WAIT A MINUTE!!! WHERE DID YOU GET THE MASS
OF 23?!
To find the mass of the most common isotope of an
atom, look at the atomic mass on the periodic table and
round it to the nearest ones place.
Sodium has a mass of 22.990. Round it to the ones
place and you get 23.
11
Using APE MAN (continued)
Sodium:
Atomic number is 11. Mass is 23.
A=P=E
11=P=E
11=11=11
11=11=11
M-A=N
23-11=N
23-11=N
23-11=12
So...
Sodium has 11 protons, 11 electrons, and 12
neutrons in a neutral atom of its most
common isotope.
12
Let’s Try One Together…
How many protons, electrons, and
neutrons are in an atom of the
most common isotope of fluorine?
A=P=E M-A=N
9=P=E 19-9=N
9=9=9 19-9=10
Protons: 9, Electrons: 9,
Neutrons: 10
13
Now You Try One…
How many protons, electrons, and
neutrons are in an atom of the most
common isotope of Neon?
A=P=E M-A=N
10=P=E 20-10=N
10=10=10 20-10=10
Protons: 10, Electrons: 10,
Neutrons: 10
14
15