GSCI 163 Lecture 2
Atomic theory What are things made of? Imagine dividing an object into smaller and smaller units. Is there a limit to how much we can divide?
Atom Means “uncuttable”. Democritus ( BC)
John Dalton (1766 – 1844) All matter is made of atoms Atoms cannot be created or destroyed. All atoms of a given element are identical in mass and properties. Different elements differ from each other because they are made of different atoms. Compounds are formed by the combination of two or more kinds of atoms in precise ratios. A chemical reaction is a rearrangement of atoms.
Is the atom indivisible? J.J. Thompson – discovery of the electron The cathode ray tube
What is the electron? Robert A. Millikan in 1906 measured the charge of a single electron
The model of the atom at this point Positive and negative charges mixed like raisin in jello
Discovery of the nucleus Ernest Rutherford in 1907 found that the atom has a nucleus made of positive particles. 100,000 smaller than the orbit of the electron
How is the nucleus held together? We need a glue to overcome electrical repulsion! New particle = neutron James Chadwick in 1932
Dmitri Mendeleev
Next class Atomic states Read handout day 3 Quiz on these topics (first min of class)