Early Early Atomic ideas

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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)

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Aristotle

• Aristotle- He did not believe in the atom idea,
  he thought matter was continuous.
• Not supported by experimental evidence

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Early 1700s

• 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.

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Late 1700s

• 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

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Law of the conservation of massby 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

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Law of definite proportionsBy 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

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Early 1800s

• 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

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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

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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.

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Law of multiple proportionsby John Dalton

• It was known that two elements combine to make
  more than one compound.
• CO
• CO2

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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.

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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.

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Modern update

• Daltons theory has been modified since the early
  1800s
• 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)

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Percent composition

• 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 35.4558.43
• composition of Na is
• (22.98 /58.43) x 100 or part over the whole
• Equals 39.32

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Percent composition

• Fe(OH) 3
• 1 Fe atom 3 O atoms 3- H atoms
• Total mass of one molecule is
• 55.8 3 ( 15.99) 3 ( 1.01) 106.80
• To find the percent iron
• (55.8 / 106.8 ) x 100 52.2

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Percent composition

• CaSO4
• Ca 40.07 amuS 32.06 amu0 15.99 amu
• Atom count?

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