John Dalton* 1800's* Studied experiments of others* Came up with a feasible theory about atoms

The Atom: smallest particle of an element that reatins the properties of the element.

Xe on nickel

CO molecules on PtMade with atomic force microscope

Dalton's Atomic Theory1. All matter is made of atoms.2. All atoms of the same element are identical.3. Atoms of different elements are not alike.4. Atoms can combine in simple, whole number ratios to form     compounds (Law of multiple proportions).  5. Atoms cannot be subdivided, created or destroyed.

Scanning Tunneling Microscope

Iron on copper

Nanotechnology

HOW WAS THE ELECTRON DISCOVERED?

* Scientists started making connections betweenmatter and charge.

I wonder how electricity would

behave in a vacuum???

* whilst happily studying electricity, Crookes saw a green flash of light (radiation struck the zinc sulfide coating). * Accidentally discovered CATHODE RAYS.

1. Cathode rays were a stream of charged particles.

2. Particles carried a NEGATIVE charge. (did not know value)

Cathode rays  = electrons

* JJ Thomson (1897)

Cathode rays were deflected by a magnet just like an electric current (­)

Cathode rays moved a small paddle wheel (had mass)

Cathode rays  = electrons

Thomson found the charge/mass ratio of an electron

* determined the mass to be much tinier than a H atom* Dalton was wrong!* Nobel Prize for Thomson in 1906! Woot!

Robert A Millikan

* found the charge of the elecron to be 1.602 x 10-19 coulombs

We call the charge of an electron 1-

* Used Thomson's charge-to-mass ratio with the calculated charge and calculated the

mass of the electron = 1/1840 of a hydrogen atom

1.  something must be in the atom to balance the charge

2.  atoms must have some type of particle to produce so much mass

PLUM PUDDING MODEL