the history of the atom from democritus to today’s modern theory

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The History of the AtomFrom Democritus to Today’s Modern Theory

Democritus• 400 BC• Proposed that all matter is made up of

atoms.• Thought atoms were small, hard particles

of different shapes and sizes.• Coined the term ‘Atom’

– From the Greek word meaning ‘Can not be divided.’

An Apothecary in his Laboratory

Alchemists

• First ‘Chemists’ around 900 AD• First to include observation and

experimentation with pure thought methods of science.

Lavoisier

• 1785• Authored the Law of Conservation of

Mass• Did experiments to prove that matter

does not disappear during a chemical reaction.

• ‘Matter can not be created or destroyed, it can only be rearranged.’

Dalton• Father of Modern Atomic Theory • 1800’s• All matter consists of atoms with space in

between.• Atoms of the same kind of element are

identical to each other.• There are as many different kinds of

atoms as there are different elements.• Atoms are solid spheres.• ‘Billiard Ball Model’

Thomson

• 1904• Inferred that atoms contain small

negatively charged particles.• He called them ‘electrons.’• He thought the electrons were dispersed

throughout a positively charged sphere.• ‘Chocolate Chip Cookie Dough Model’

Rutherford

• 1911• Famous Gold Foil Experiment• Discovered and named the ‘nucleus’ of

the atom.• Proposed that most of the mass and all of

the positive charges of an atom are in its nucleus.

• ‘Peach Pit Model’

Rutherford’s Gold Foil Experiment

Peach Pit Model

Bohr

• 1913• Concluded that electrons travel in fixed

orbits around the nucleus based on the amount of energy they contain.

• He called the ‘orbits’ Energy Levels.• ‘Solar System Model’

Erwin Schrodinger and Werner Heisenberg

Schrodinger and Heisenburg

• 1926• Scientists described the electron region of

the atom as a cloud around the nucleus.• This cloud area shows that electrons do

not orbit the nucleus in definite paths, but are likely to be in a given region at any particular time.

• ‘Modern Electron Cloud Model’

Modern Electron Cloud Model

Chadwick

• 1932• Worked with E. Rutherford in the

discovery of a third sub-atomic particle.• He concluded this particle to be free of

electrical charge and he called it the ‘neutron.’

• Concluded it was located in the nucleus along with the protons.

Today’s Newest Members:

Quarks and Leptons• Particles within particles.• Protons and Neutrons are made of

Quarks:Up DownStrange TopCharm Bottom

• Electrons are a small thin type of Lepton.

And now you know the rest of the story!!The End.

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