Transcript Atomic Structure and the Periodic Table Continued

Atomic Structure and the
Periodic Table Continued
Atomic Mass
Mass = the amount of matter in an object
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What does an atom weigh?
Unit of Measurement = Atomic Mass Units or u
1u = 1.67 X10-24 g
or
0.00000000000000000000000167 g
This is a REALLY SMALL NUMBER!!!!!
Mass Number
Mass Number = the sum of the number of
protons and neutrons in the nucleus of an
atom
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Protons and Neutrons each have a mass
around 1 u
Example: An atom has 6 protons and 6
neutrons: What is the mass number?
6 protons + 6 neutrons = 12 u Carbon
How Do You Know How Many
Neutrons Are In An Atom
Subtract the Atomic # (which equals the #
of Protons) from the Mass #
Important Point: Atomic mass and thr
mass # are not the
same thing
Atomic Mass
HUH!!!!!!
To get the mass number from the atomic
weight, either round the atomic weight up
or down (.0 - .49 round down; .5 - .99
round up):
Example: Oxygen
Atomic Mass = 15.9994
Mass Number = 16
Back to the original question:
For Oxygen the mass number is 16 and
the number of protons is 8
16 mass # – 8 Protons = 8 Neutrons
Do all atoms of the same element
have the same number of neutrons?
No, they can be different
Atoms of the same element that have
different number of neutrons are called:
Isotopes!!!
Isotopes
How are isotopes written:
The top number is the mass # and the bottom
number is the atomic number
To get the # of neutrons just subtract the two
numbers
Why are isotopes important?
Isotopes are used in radiometric dating
Used in ecological studies
Biochemical Studies
Cancer therapies
Forensics
What does having different # of
neutrons mean for the element?
This means the different isotopes of the
same element have different masses!!!!
Average Atomic Mass:
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The average mass of a mixture of its isotopes
This is the number we find on the periodic
table of elements