Transcript How did different scientists contribute to atomic theory?

How did different scientists
contribute to atomic theory?
Democritus
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He asked this question: If you break a piece of matter in
half, and then break it in half again, how many breaks
will you have to make before you can break it no further?
Democritus thought that it ended at some point, a
smallest possible bit of matter. He called these basic
matter particles, atoms.
Benjamin Franklin
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His famous stormy
kite flight in June of
1752 led him to
develop the idea that
matter had charges
which he represented
using plus(+) and
minus (-).
JJ Thompson
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In 1897, Thompson discovered the first component
part of the atom: the electron, a particle with a
negative electric charge.
In 1904, he proposed an initial model of an atom,
since nicknamed "Thompsons pudding".
He imagined the atom as a sphere full of an
electrically positive substance mixed with negative
electrons "like the raisins in a cake".
Robert Millikan
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What Millikan did was
to put a charge on a
tiny drop of oil, and
measure how strong
an applied electric
field had to be in
order to stop the oil
drop from falling.
He determined the
charge on an electron
Ernest Rutherford
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In 1912, Rutherford (New
Zealand physicist) discovered
the atomic nucleus.
Neils Bohr
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The planetary model
was proposed by
Bohr after studying a
hydrogen atom in
1915.
Electron Cloud Theory
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Which element has
the atomic # 10?
Which element has a
mass of 4 amu?
Which element is in
period 3 and is a
Noble Gas?
64
29
Cu
+2
How many protons?
How many electrons?
How many neutrons?
How do we determine average
atomic mass?
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An element can exist in a number of forms,
called isotopes.
What is an isotope?
Isotopes are forms of the same atom that vary in
mass (same # of protons different # of neutrons)
To find the AVERAGE ATOMIC MASS of an
atom, we take into account all of the isotopes
that exist and the percentage of each type.
Let’s determine the average atomic
mass of carbon!
Carbon exists naturally as two isotopes;
Carbon-12 and Carbon-13
 The % abundance (fractional abundance)
for C-12 is 98.93% and for C-13 is 1.07%
 (12) x (0.9893) = 11.8716 amu
 (13) X (0.0107) = 0.1391 amu
12.0107 amu
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