Transcript Early Early Atomic ideas

Early Early Atomic ideas
• 400 BC, Democritus – said world was made up of
two things air and a basic particle called an atom.
• Atom was the smallest piece of matter and could
not be broken down further.
• Not supported by experimental evidence
• Trivia – word origin – Greek Atemnein – which
means not cuttable ( a – non) (temnein – cuttable)
Aristotle
• Aristotle- He did not believe in the atom
idea, he thought matter was continuous.
• Not supported by experimental evidence
Early 1700’s
• Knew about elements
• Elements could not be broken down.
• Knew elements combined to make a new
substance with different properties.
• Did not know if a particular compound was
always the same ratio or combination of
elements.
Late 1700’s
• Quantitative analysis
• mass balances were improved, now they
could accurately measure the masses of the
elements and the compounds.
• This led to the discovery of certain laws
Law of the conservation of mass
by Antoine Lavoisier
• Mass can neither be created nor destroyed during
ordinary chemical reactions or physical changes.
• Used a closed system- a system that can not
change matter with its surroundings
• Conducted chemical reactions and found that the
mass of the reactants always equaled the mass of
the products.
– Reactant mass
= product mass
Law of definite proportions
By Joseph Proust
• A chemical compound always contains the
same elements in the same proportions by
mass regardless of the size of sample or
source of the compound.
• Specific substances always contain
elements in the same ratio by mass.
• NaCl is always 1 sodium atom and 1
chlorine atom
Early 1800’s
• Dalton, John
• Schoolteacher
• His work was based on the work of Proust and
Lavoisier
• Developed the Atomic theory which has 5 main
points
• The atomic theory provided an explanation of both
laws and then developed his own Law of multiple
Proportions
• Was supported by experimental evidence
Daltons Atomic Theory
1. All matter is composed of extremely small
particles called atoms.
2. Atoms of a single element are all identical
in size, mass ,and other properties.
Atoms of different elements would differ in
size, mass, and properties
Dalton continued
3. Atoms can not be subdivided , created or
destroyed
4. Atoms of different elements combine in
simple whole number ratios to form
chemical compounds.
5. In chemical reactions, atoms are combined,
separated, or rearranged.
Law of multiple proportions
by John Dalton
• It was known that two elements combine to
make more than one compound.
– CO
– CO2
Multiple proportions continued
• If two or more different compounds are
composed of the same two elements, then
the ratio of the mass of the second element
combined with a certain mass of the first
element is always a ratio of small whole
numbers.
Multiple proportions – now
common sense
• You can not add half an atom to an atom, if
you combine atoms you must add an entire
atom.
• Atoms react as whole units, they can not be
divided into smaller parts.
• Therefore, mass increases in whole number
ratios.
Modern update
• Dalton’s theory has been modified since the early
1800’s
• We now know that
– Atoms are divisible into electrons, protons and neutrons
and even smaller yet into quarks and gluons etc.
– We also now know that all atoms of a particular
element may differ slightly in mass. These are called
isotopes ( same # protons, different # neutrons)
Percent composition
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NaCl
1 atom of Na and 1 atom of Cl
Look up atomic masses of each element
Na = 22.98 amu and Cl = 35.45 amu
Total mass of NaCl is 22.98 + 35.45=58.43
% composition of Na is
• (22.98 /58.43) x 100 or part over the whole
• Equals 39.32 %
Percent composition
• Fe(OH) 3
• 1 Fe atom; 3 – O atoms; 3- H atoms
• Total mass of one molecule is
–
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55.8 + 3 ( 15.99) + 3 ( 1.01) = 106.80
To find the percent iron
•
(55.8 / 106.8 ) x 100 = 52.2%
Percent composition
• CaSO4
• Ca= 40.07 amu;S= 32.06 amu;0 =15.99 amu
• Atom count?