Transcript Atomic Theory

The Periodic Table
• 1868
• Was organized according to the
properties of the known
elements
• Dmitri Mendeleev noticed that
when the elements were put
into order by their atomic
mass, some of their properties
repeated periodically
Dmitri Mendeleev
•Noticed that properties repeat, e.g.
melting point, react with
oxygen, density, mass…
Periodic Table
• So he put them in columns with
others that are similar.
• Didn’t know anything about
protons, electrons, etc. Just
made observations!
• Even made some guesses about
ones that were missing and
their properties. He was
correct!
Guesses
• Eka-Aluminum:
– Atomic Mass 68, density 5.9
• Gallium (Ga):
– Atomic mass 69.7, density 5.94
• Eka-Silicon:
– Atomic Mass 72, density 5.5
• Germanium (Ge):
– Atomic Mass 72.6, density 5.7
Atomic Theory
• Democritus …5th century
BCE
• Matter is made up of
atoms
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–
–
–
Atoms are solid
No internal structure
Different sizes
Space in between them
(void)
Atomic Theory
• John Dalton … 1800’s
• Father of modern atomic
theory
• Discovered atomic weights
and symbols for elements
• elements made of atoms
• atoms of an element same mass
• different elements have different
masses
• Atoms combine in small, ratios
such as 1:1, 1:2, 2:3
• atoms can’t be created or
destroyed
Atomic Theory
• JJ Thompson … 1897
• Discovered electron
(first subatomic
particle)
• Believed atoms had
negative charges
floating in a sea of
positive ones, like
chocolate chips in a
cookie
• Called plum pudding
model
Atomic Theory
• Earnest Rutherford
… 1911
• Discovered nucleus
of atom and said
it was positive
• Electrons orbit
through empty
space around
positive nucleus
Atomic Theory
• Niels Bohr … 1914
• Discovered energy
levels for electrons
• Farther away from
nucleus, higher
energy level
• Planetary model… like
planets orbiting
sun
Atomic Theory
• Quantum theory
• Current theory
• Electrons don’t have
orbits like planets
• They move to fast to
know exactly where
they are, but we can
tell where they
probably are
• Electron cloud is place
where they probably
are
Electron cloud
• Broken down into energy levels
• Energy levels have sublevels called orbitals
• Energy levels and orbitals only hold a certain
number of electrons maximum
• Called s p d f