Download ATOMIC STRUCTURE

 Protons,
neutrons, electrons too
 Make up the atoms all around you!
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Nucleon – general term for nuclear particles.
What are nuclear particles?
Protons – positively charged particles in the
nucleus of an atom that identifies the element:
atomic number on the periodic table: has a mass
of ~1 amu
Neutrons – neutral particles in the nucleus of
an atom: number may vary: has a mass of~ 1
amu
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Electrons – negatively charged particles found
in orbitals outside the nucleus (electron cloud):
determines the reactivity of the atom: have
virtually no mass ( 1/1840 amu)
Sum of protons and neutrons gives the mass
number (weight) of the atom
amu is based on 1/12 of the carbon-12 atom – a
reference isotope
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What’s an isotope?
Atoms of the same element having different
numbers of neutrons (therefore different
masses) are called isotopes.
They have the same number of protons
(identity stays the same).
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Ex. Hydrogen has 3 isotopes
hydrogen – 1, hydrogen – 2, and hydrogen -3
May be represented several ways.
H-1, hydrogen-1, 1H1, 1H, (nuclide)
Mass number as a superscript and atomic
number as a subscript. May see both on the left
side of element symbol.
Which do you think is the most abundant
isotope? (hint: look at the periodic table)
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Mass number on the periodic table is actually
the average atomic mass – a weighted average
based on the percent abundance of the
naturally occurring isotopes. That’s why they
almost always have decimals!
A mass number is usually a whole number, sum
of protons and neutrons – can’t have just a
piece of a neutron or proton in an atom.
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Copper exists as a mixture of two isotopes.
Cu-63 makes up 69.17% of copper atoms and
Cu-65 makes up 30.83% of copper atoms. If
the atomic mass of Cu-63 is 62.930 amu and
the atomic mass of Cu-65 is 64.928 amu,
calculate the average atomic mass of copper
based on the percent abundance of the two
isotopes.
Isotope
Abundance
Atomic mass (amu)
Ga-69
60.108%
68.926
Ga-71
39.892%
70.925