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How did different scientists contribute to atomic theory?. Democritus. 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?

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How did different scientists contribute to atomic theory?


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Presentation Transcript
democritus
Democritus
  • 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
Benjamin Franklin
  • 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
JJ Thompson
  • 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
Robert Millikan
  • 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
Ernest Rutherford
  • In 1912, Rutherford (New Zealand physicist) discovered the atomic nucleus.
neils bohr
Neils Bohr
  • The planetary model was proposed by Bohr after studying a hydrogen atom in 1915.
slide9
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
How do we determine average atomic mass?
  • 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
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