Unit 2 Day 1
February 16, 2017
Date: February 16, 2017
Before you go you should know the subatomic particles and how to find
average atomic mass.
WARM-UP:
What are the 3 major subatomic particles and where are they located?
outside nucleus
inside nucleus
inside nucleus
Unit 2 Day 1
February 16, 2017
Unit 2 Day 1
February 16, 2017
Unit 2 Day 1
February 16, 2017
erase to reveal
number of protons
number of neutrons
number of electrons
Atomic number
Mass Number
9
19-9= 10
9
9
19
number of protons
number of neutrons
number of electrons
Atomic number
Mass Number
35
80-35=45
35
35
80
Unit 2 Day 1
February 16, 2017
If an element has an atomic
number of 34 and a mass
number of 78 what is the :
–number of protons
34
–number of neutrons
78-34=44
–number of electrons
34
–Complete symbol
78
34
If an element has 91 protons
and 140 neutrons what is the
–Atomic number 91
–Mass number 140 + 91=231
–number of electrons
–Complete symbol
231
Se
91
Pa
91
Unit 2 Day 1
February 16, 2017
Isotopes
Atoms of the same element can have different numbers of
neutrons, different mass numbers, called isotopes.
We can put the mass number after the name of the element.
carbon- 12
carbon -14
uranium-235
Measuring Atomic Mass: Unit is the Atomic Mass Unit (amu)
[One-twelfth the mass of a carbon-12 atom.]
Each isotope has its own atomic mass, thus we determine the
average from percent abundance. (If not told otherwise, the mass
of the isotope is the mass number in amu)
Calculating averages: Multiply the atomic mass of each isotope by
it’s
its abundance (expressed as a decimal), then add the results.
Unit 2 Day 1
February 16, 2017
Formula:
% x mass + % x mass + % x mass + ...
100
Unit 2 Day 1
February 16, 2017
Example: Calculate the atomic mass of copper if copper has two
isotopes. 69.1% has a mass of 62.93 amu and the rest has a mass
of 64.93 amu.
63.55 amu
Unit 2 Day 1
February 16, 2017
Find the average atomic mass of silver if
51.83% if the silver atoms occurring in
nature have mass 106.905 amu and
48.17% of the atoms have mass 108.905
amu.
107.868 amu