Four ElementsScientist: Empedocles
Theory/Discovery: Everything is made up of the four elements; earth, air, water, fire
Details: The elements were thought to each share characteristics; dry, wet, hot and cold. Empedocles check this theory and determined that since air takes up space, it is a form of matter (click on photos to enlarge)
The AtomScientist: Democritus
Theory/Discovery: All matter can be continually divided until a singe particle is reached. The particle was named "the atom" as atom means "cannot be cut"
Details: Democritus then proposed that atoms are
-Of different sizes
-In constant motion
-Separated by empty spaces
Belief of the Four ElementsScientist: Aristotle
Theory/Discovery: The four elements
Details: Aristotle believed in Empedocles's four elements theory and because of his influence and writings, lead the world to believe as well for almost 2000 years.
ElementsScientist: Robert Boyle
Theory/Discovery: Elements are simple unmitigated bodies
Details: Robert Boyle rejected the four-element theory and came up with his own theory, known as the modern definition of elements. Boyle also believed that air was a mixture and not an element
Oxygen as an ElementScientist: Joseph Priestley & Antoine Lavoisier
Theory/Discovery: Air is a mixture
Details: Joseph Priestley isolated oxygen but then Antoine Lavoisier realized that it was an element. He then experimented to find that air was a mixture of oxygen and at least one other gas
HydrogenScientist: Henry Cavendish
Theory/Discovery: Hydrogen and that water is a mixture
Details: Henry Cavendish mixed metal with acid and created hydrogen. He discovered that hydrogen would burn in oxygen and produce water
Billiard Ball Model (Atomic Model)Scientist: John Dalton
Theory/Discovery: Billard ball model
Details: John Dalton's atomic model stated that
-All matter is made of atoms which are particles too small to see
-Each element has its own kind of atom with its own mass
-Compounds are created when atoms of different elements link to form molecules
-Atoms can not be created nor destroyed or subdivided in chemical changes
IonsScientist: Micheal Faraday
Theory/Discovery: Electric currents can cause chemical changes in some compounds and solutions
Details: The atoms gain the electric charges and form charged atoms that are called "Ions". Micheal Faraday modified Dalton's billiard ball model, concluding that...
-Matter must contain positive and negative charges
-Opposite charges attract and like charges repel
-Atoms combine to form molecules because of electrical attractions between atoms
ElectronScientist: J.J. Thompson
Theory/Discovery: Negatively charged particles can be emitted by very hot materials.
Details: Thompson concluded that the particles emitted must be negatively charged because when he experimented they were attracted to the positive end of the circuit. Thomson theorized that
-Atoms contain negatively charged electrons
-Since Atoms are neutral, the rest of the atom is a positively charged sphere
-Negatively charged electrons are evenly distributed throughout the atom
NucleusScientist: Ernest Rutherford
Theory: Small positively charged mass in the middle of the atom
Details: Rutherford tried sending positively charged particles through a thin piece of foil, suspecting that they would go through, but then as some deflected at large angles, he realized they were colliding with a mass in the middle of the atom.
Nucleus Cont.Rutherford concluded that...
-The center of the atom contains most of the atom's mass, but not much area. The nucleus is what made some of the particles bounce back unexpectedly
-The nucleus is surrounded by negative electrons
-Most of the atom is empty
ProtonScientist: Ernest Rutherford
Theory/Discovery: Protons in the nucleus
Details: rutherford found that protons alone could not account for the nucleus' ass and there must be another particle inside. This third particle had the same mass as the proton but was neutral in charge
NeutronScientist: James Chadwick
Theory/Discovery: Particles that could easily penetrate and disintegrate atoms
Details: Chadwick realized that the particles have zero charges and are neutral and that there are more undetected particles in the atom. Chadwick proposed that
-Atoms are empty spheres with dense nucleus'
-The nucleus contains positive protons and neutral particles (neutrons)
-Negative electrons circle the space around the nucleus
-A neutral atom has the same number of protons as electrons
Continuation of the Belief of the Four ElementsScientist: Alchemists
Theory: Metals ripen into gold
Details: The alchemists tried to grow gold from cheaper metals but had no success. Though failing to grow gold the alchemists came up with the chemical symbols for elements and compounds, and many common lab tools still used today.