Atomic Theories A timeline…. or as you may prefer to remember it…

THE STRUCTURE OF THE ATOM(CHAPTER 4) Atomic Theories

A timeline…

EARLY GREEK THEORY

or as you may prefer to remember it…

DEMOCRITUS (GREEK~400B.C.)

I believe atoms are the smallest pieces of matter.

MORE ON DEMOCRITUS He came up with the term “atom” He thought atoms had different shapes

and sizes He thought they were indivisible and

indestructible “atomists” – people who followed his

beliefs

ARISTOTLE (GREEK~350 B.C.) His beliefs were more likethe early Greeks Philosopher

Atoms? Give me a break! I could speak for hours

against their existence.

JOHN DALTON (ENGLAND~1800)

Dalton’s Atomic TheoryMatter is composed of atomsAll atoms of the same element are identical;

different elements have unique atomsThey cannot be destroyed or createdThey combine to form compounds

JJ THOMSON (ENGLAND – 1897) Discovered the electron Proved the atom can be divided Plum pudding model

ERNEST RUTHERFORD (ENGLAND – 1909) Atoms have a dense “nucleus” Discovered the proton

JAMES CHADWICK (ENGLISH – 1932) Discovered the neutron

IMPORTANT STUFF

ATOMIC NUMBER The number of protons in an atom Usually the number of electrons also

MASS NUMBER The number of protons and neutrons The “rounded” number Neutrons = mass number – atomic

number Isotopes – atoms possessing the same

number of protons but different neutrons

ATOMIC MASS The “unrounded” number It’s an average “mass” of all the atoms

of an element in nature