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Atomic Number- the number of protons in
the nucleus of an atom of that element
Ex: Hydrogen atoms have only one proton in
the nucleus, so the atomic number is 1.
Atoms are neutral, so the # of protons =# of
electrons.
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Total number of protons and neutrons in an
atom.
Mass = # protons + # neutrons
The # of neutrons in an atom is the difference
between mass # and atomic #.
# Neutrons = Mass # - Atomic #
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Atoms that have the same # of protons, but
different # of neutrons.
If they have more/less neutrons, then the
mass number will be different!
Have same number of protons and electrons.
Only difference is # of neutrons!
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A way to measure the mass of an atom, using
a standard (carbon-12).
Carbon-12 has 6 protons and 6 neutrons.
It’s mass is set at 12 amu. So the mass of a
single proton or neutron is about 1 amu.
Atomic Mass- weighted average mass of the
atoms in a naturally occurring sample of the
element.
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Ca
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P-3
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Al+3
1.
2.
3.
Change abundance percents into decimals.
Multiply the mass of each isotope by its
natural abundance. (expressed as decimal)
Add the products.
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Element X has two natural isotopes. The isotope
with a mass of 10.012 amu has a relative
abundance of 19.91%. The isotope with a mass of
11.009 amu has a relative abundance of 80.09%.
Calculate the atomic mass and identify this
element.
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The element copper has naturally occurring
isotopes with mass numbers of 63 and 65.
The relative abundance and atomic masses
are 69.2% for mass = 62.93 amu, and 30.8%
for mass = 64.93 amu. Calculate the average
atomic mass of copper.
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Calculate the atomic mass of bromine. The
two isotopes of bromine have atomic masses
and relative abundance of 78.92 amu
(50.69%) and 80.92 amu (49.31%).