# Determining the number of atomic particles in an element by pptfiles

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```									Determining the number
of atomic particles in an
element
Step one

Find the element on
the periodic table.
Find oxygen.

1. Find the
element on the
periodic table.
Step Two

•Find the number
of protons (+).
8
O
oxygen
15.99

2.Find the number of
protons (+).
A. Atomic # = number of
protons
Hint: Find the atomic
number.
• The atomic number is
equal to the number
of protons (+)
8
O
oxygen
15.99
Eight is the atomic
number.

•This means oxygen
has 8 protons (+).
8
O
oxygen
15.99
Check for Understanding

• How many protons (+)
does copper have?

29            29
Cu
Copper   protons
63.55
Check for Understanding

• How many protons (+)

82          82
Pb
207.20
Step Three

•Find the number
of electrons (-).
8
O
oxygen
15.99
Hint: Find the atomic
number.
• The atomic number is
equal to the number of
electrons (-) in a neutral
atom.
8
O
oxygen
15.99
Whoa! What is a neutral
atom?

• Neutral means not positive
and not negative. So the
number of protons (+) have
to equal the number of
electrons (-) to cancel each
other out.
So if eight is the atomic
number of oxygen.

• Then oxygen has 8 protons
(+).
• Which means oxygen has 8
electrons (-).
8
O
oxygen
15.99
Check for Understanding

• The number of + will
always EQUAL the
number of - in a neutral
atom.
• # of protons = # of electrons
Check for Understanding

• How many electrons (-)
does copper have?

29            29
Cu
Copper   electrons
63.55
Check for Understanding

• How many electrons (-)

82          82
Pb
207.20

3.Find the number of
electrons (-).
A. # of protons = # of
electrons
Now What!?!

• The atomic number gives
us the number of protons
(+) and the number of
electrons (-).
• A.P.E.
• Atomic # = Proton # = Electron #
Now What!?!

• But how do we get the
number of neutrons (no
charge)?
Step four--number of neutrons

• To get the the number of
neutrons, we have to do
TWO things
• Round the atomic mass.
• Subtract the atomic
number from the rounded
atomic mass.
Where is the atomic
mass?

•The bottom number
is the atomic mass.
8
O
oxygen
15.99
What is the atomic
mass?
• The atomic mass is the average
mass of one atom of that
element.
• One atom of Oxygen has a
mass of 15.99 amu. 8
O
oxygen

15.99
Round the atomic mass.

• To round to the nearest
WHOLE NUMBER, you look
at the tenths column..
8
For oxygen, the             O
oxygen
number in the tenths
column is 9                15.99
Round the atomic mass.

• If the number in the tenths
column is 5, 6, 7 , 8 or
9…you add one to the ones
column.
8
For oxygen, the                 O
oxygen
rounded amount is
16.
15.99
Round the atomic mass.

• If the number in the tenths
column is 4, 3, 2, 1 or 0, you
simply drop the decimals.
For magnesium,           12
the rounded                   Mg
magnesium
amount is 24.              24.30
Okay, so we have rounded
the atomic mass..NEXT?
• To get the the number of
neutrons, we have to do
TWO things
• Round the atomic mass.
• Subtract the atomic
number from the rounded
atomic mass.
Subtract the atomic number
from the rounded atomic mass.
• The rounded atomic mass
for oxygen is 16.
•The atomic number is 8.
16              8
- 8
_________
O
8                  oxygen

15.99
So the number of neutrons
is … 8.
• The rounded atomic mass
for oxygen is 16.
•The atomic number is 8.
16              8
- 8
_________
O
8 neutrons         oxygen

15.99

4. To find the number of
neutrons
A. Round the atomic mass.
B. Subtract the atomic
number from the rounded
atomic mass.
Check for Understanding

• How many neutrons (o)
does copper have?
64
- 29
_______
29            35
35              Cu
Copper   neutrons
63.55
Check for understanding

• Number of protons? 12
•Number of electrons?    12
•Number of neutrons?
12
24
-_________
12                       Mg
magnesium
12 neutrons            24.30