THE ATOM MODEL

THE MODEL OF AN ATOM HAS CHANGED

• Over 2 centuries
• Different models have been thought of
• Atoms have been learned more about

DEMOCRITUS

• Matter is made of small, solid objects
• These objects can't be divided
• They also can't be created or destroyed
• They were called atomos
• Greek philosopher

JOHN DALTON (1766-1844)

• Created the first atomic theory
• English school teacher
• Viewed atoms as tiny, solid balls
• His atomic theory had 4 statements
• Atoms combine in specific ratios

DALTONS THEORY

• Atoms are tiny, invisible particles
• Atoms of one element are all the same
• Atoms of different atoms are different
• Compounds form by combining atoms

J.J THOMSON(1856-1950)

• Discoved electrons
• First scientist showing that atoms are made of smaller things
• Proposed the exsitiance of a (+) particle
• Had an experiment called Cathode Ray Tube Experiment

ERNEST RUTHERFORD (1871-1937)

• Discovered protons and the nucleus
• Showed atoms have (+) particles in the center
• Mostly empty spaces in those centers
• (+) particles called protons
• Center called nucleus

NIELS BOHR (1885-1962)

• Improved Rutherford's model
• Student of Rutherford's
• Proposed that electron move around the nucleus in layers
• These layers are called shells
• Every atom has a specific number of electron shells

JAMES CHADWICK(1891-1874)

• Discovered neutrons
• Discovered particles with no charge
• Thoses particles are called neutrons
• Neutrons also found in the nucleus

THE MODERN MODEL (1932-)

• New model has electrons moving around the nucleus
• The electron moving are in a cloud
• Its impossible to know where electrons are at any time