The Parts of an Atom

J.J. Thomson

•He experimented with cathode ray tubes

•He passed electricity through the tube and discovered the first subatomic particle – the electron

•He developed the plum pudding model of an atom

Plum Pudding Model

Robert Millikan

•He determined that the electron has a negative charge

•He determined the mass of the electron

Ernest Rutherford

•He proved the plum pudding model was incorrect with the gold foil experiment

Gold Foil Experiment

positive alpha

particles

•He discovered the nucleus of the atom!

•The nucleus is the dense, positively charged center of the atom

•He came up with the Nuclear Atomic Model

NucleusElectron

Nuclear Atomic Model

•Years later, Rutherford discovered the proton

•proton = a positively charged particle inside the nucleus

+nucleus

proton

James Chadwick

•worked with Rutherford

•discovered the neutron – a particle in the nucleus with the SAME MASS as a proton, but with NO charge (it’s neutral)!

Modern Atomic Structure

•spherically shaped

•most of atom’s mass is in the nucleus (99.7%)

•nucleus surrounded by negative electrons

•Atoms have no charge (they are electrically neutral) because the number of protons is equal to the number of electrons

3 protons (+)

3 electrons (-)

++ +

-

-

-

particle symbol location charge mass (g)relative

mass

electron e –

in space aroundnucleus

– 9.11 x 10 – 28 _1__1840

proton p+ insidenucleus + 1.673 x 10 –

241

neutron n0 inside

nucleus

nocharg

e

1.673 x 10 –

241

*Electron has the least mass

You Made It!!!