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Atoms and Moles
The Atomic Theory
• As far back as 400 BC, people believed that
the atomic theory existed.
• The atomic theory basically stated that
atoms are the building blocks of all matter.
• This theory had no experimental results to
back it up at the time.
John Dalton
• In 1808, an English schoolteacher named John
Dalton used the Greek concept of the atom along
with 3 other scientific laws to develop an atomic
theory.
• He believed that all matter was made up a few
kinds of atoms.
• He also stated that all elements were made up of
only one type of atom and that compounds were
made up of two or more types of atoms.
Dalton’s Atomic Theory
• All matter is composed of extremely small
particles called atoms that cannot be subdivided,
created, or destroyed.*
• Atoms of a given element are identical in their
physical and chemical properties. *
• Atoms of different elements combine in simple,
whole number ratios to form compounds.
• Atoms of different elements differ in their physical
and chemical properties.
• In chemical reactions, atoms are combined,
separated, or rearranged but never destroyed,
created, or changed.
The Laws Involved:
• The Law of Conservation of Mass: The mass of
reactants equals the mass of the products in a
chemical reaction. Mass cannot be created nor
destroyed.
• The Law of Multiple Proportions: If two or more
different compounds are composed of the same
elements, the ratio of the masses of the second
element is always the ratio of small whole
numbers.
• Law of definite proportions: Samples of a given
compound are made with the same elements in
exactly the same proportions by mass regardless
of the size or the source of the samples.
Electrons
• Electrons were discovered
in the mid-1800’s by J.J.
Thompson.
• The electron has a
negative charge and is
depicted as e,e-, 0-1 e.
• It’s charge is -1.602x10 -19
C.
• It’s mass is 9.109x10-31
kg.
Cathode ray tube
• The cathode ray tube
was used by JJ
Thompson to discover
electrons.
• Magnets or charged
plates can be used to
attract or deflect the
beam which proved
that the beam had a
negative charge.
Protons
• Protons were discovered
shortly after the electron.
• The proton has a positive
charge and is depicted as
p,p+, or 1+1p.
• It’s charge is +1.602x10-19
C.
• The mass of a proton is
1.676x10-27 kg.
Neutrons
• Discovered by British
scientist James Chadwick.
• Neutrons carry no charge.
They are electrically
neutral.
• The charge is 0 C.
• They can be depicted as n
or 01n.
• The mass of a neutron is
1.675x10-27 kg.
Gold Foil Experiment
• Rutherford’s gold foil
experiment surprised
researchers by
showing that atoms
were mostly made up
of space.
• It also proved that
atoms had a dense,
positively charged
area called the
nucleus.