1. How did different scientists contribute to atomic theory?

2. 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? 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. Democritus thought that it ended at some point, a smallest possible bit of matter. He called these basic matter particles, atoms.

3. Aristotle Greek philosopher who disagreed with Democritus. He believed that you never end up with a particle which can be cut. Greek philosopher who disagreed with Democritus. He believed that you never end up with a particle which can be cut. Democritus was right…An atom is the smallest particle into which an element can be divided and still be the same substance! Democritus was right…An atom is the smallest particle into which an element can be divided and still be the same substance!

4. 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 (-). 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 (-).

5. JJ Thompson In 1897, Thompson discovered the first component part of the atom: the electron, a particle with a negative electric charge. 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". 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". He imagined the atom as a sphere full of an electrically positive substance mixed with negative electrons "like the raisins in a cake".

6. Ernest Rutherford In 1912, Rutherford (New Zealand physicist) discovered the atomic nucleus. In 1912, Rutherford (New Zealand physicist) discovered the atomic nucleus.

7. Neils Bohr The planetary model was proposed by Bohr after studying a hydrogen atom in 1915. The planetary model was proposed by Bohr after studying a hydrogen atom in 1915.

8. Electron Cloud Theory or Modern Atomic Theory

9. Which element has the atomic # 10? Which element has the atomic # 10? Which element has a mass of 4 amu? Which element has a mass of 4 amu? Which element is in period 3 and is a Noble Gas? Which element is in period 3 and is a Noble Gas? 64 64 29 Cu +2 29 Cu +2 How many protons? How many electrons? How many neutrons?

10. How do we determine average atomic mass? An element can exist in a number of forms, called isotopes. An element can exist in a number of forms, called isotopes. What is an isotope? What is an isotope? Isotopes are forms of the same atom that vary in mass (same # of protons different # of neutrons) 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. 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.

11. Let’s determine the average atomic mass of carbon! Carbon exists naturally as two isotopes; Carbon-12 and Carbon-13 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% The % abundance (fractional abundance) for C-12 is 98.93% and for C-13 is 1.07% (12) x (0.9893) = 11.8716 amu (12) x (0.9893) = 11.8716 amu (13) X (0.0107) = 0.1391 amu (13) X (0.0107) = 0.1391 amu 12.0107 amu