MODELS OF MATTER The history as we know it

Models of Matter 450 B.C. Empedocles (Greek) Matter made up of only 4 elements –Earth, Air, Fire, Water

Models of Matter 400 B.C. Democritus First atomic theory Not widely accepted – went against views of Socrates

Models of Matter 350 B.C. Aristotle defends the 4 element model

Models of Matter Four element model survives into the 1600’s despite numerous advances in scientific equipment and understanding

Models of Matter 1650 A.D. Robert Boyle Definded ‘element’ as a pure substance that can’t be broken down Believed air was a mixture, not an element

Models of Matter 1700’s A.D. Henry Cavendish Discovers hydrogen gas by mixing acid and a metal Later finds that water not an element (burning hydrogen in oxygen made water)

Models of Matter 1800’s A.D. Generally accepted that matter was made of elements …enter John Dalton…

Models of Matter 1808 A.D. John Dalton Atom is a featureless sphere with no p+, e- or n (like a billiard ball) Atoms are indivisible

Models of Matter 1897 A.D. J.J. Thomson Sphere is positive with imbedded electrons (like a raisin bun) Net charge of zero No p+ or n

Models of Matter 1904 A.D. Hantaro Nagaoka Sphere is positive but electrons orbit in a ring (like planet Saturn) Still no p+ or n

Models of Matter 1914 A.D. Ernest Rutherford Small, positive nucleus surrounded by electrons (like bees around a beehive) Still no neutrons We’re getting closer!

Rutherford’s Gold foil experiment

Models of Matter 1921 A.D. Niels Bohr Built on Rutherford’s work Special numbers of electrons in discrete energy levels Similar to planets orbiting the Sun