The Modern Nuclear Atom How did our concept of the atom come about, and how did it develop?

The Modern Nuclear Atom

How did our concept of the atom come about, and how did it develop?

Democritus460-370 ADPhilosopher in Thrace (Greece)“Father of Modern Science”

All matter is made of atoms.Between the atoms is empty space.The atoms have the qualities of the material

that they make up.Atoms are uncuttable spheres.

Greek atomos means ‘indivisible’ or uncuttable.

John Dalton

1766-1844

Developed Greek atomos concept.

Dalton’s Atomic Theory

#3 is called the Law of Definite Proportions: Atoms combine in whole-number ratios to make molecules: 2 H atoms and 1 O atom make 1 H2O molecule.

They differ only intheir masses.

#4 is called the Law of Conservation of Mass (or Matter)“In an ordinary chemical reaction, mass is neither lost nor gained,because the atoms simply re-arrange into new molecules. No atomsare ever lost or gained.”

J.J. Thompson1890’s, invents the cathode ray tube.Discovers that ‘cathode rays’ are beams of charged particles (electrons).Electrons come from inside atoms and have negative charges.

If negatively charged particlesexist, then they must bebalanced by positively-chargedparticles.

Ernest Rutherford

Gold Foil Experiment

Discovers that atoms have a tinynucleus in the center. Nucleuscontains the + charges.

James Chadwick

Discovers the neutron.