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500 BCE
Democritus
He devolved the concept that an atom can not be broken down and is the smallest particle.Democritus hypothesized that atoms cannot be destroyed, differ in size, shape and temperature, are always moving, and are invisible. He believed that there are an infinite number of atoms. -
Antoine Lavoisier Law of Conservation of Mass
His methods he was able to determine correctly what was happening during the combustion of metals.The Law of Conservation of Mass states that during chemical reactions matter is neither created or destroyed. The mass of the reactants should be equivalent to the mass of the products. -
Joseph Proust Law of Definite Proportions
This law states that a compound is composed of exact proportions of elements by mass regardless of how the compound was created. For example, to make water there is a specific ratio of grams of hydrogen to grams of oxygen regardless of where your sample of water was found. All water has this particular proportion. -
Dalton's Atomic Model
He proposed that all matter is composed of very small things.
He stated the following:
-Matter is made up of small particles
-Atoms are indestructible
-Atoms of an element are identical
-Atoms of different elements have different masses
-Compounds are formed by combining atoms of different elemets -
Rutherford's Gold Foil Experiment
He proved the existence of a small massive center to atoms. Later after this was found the name of it changed to the nucleus of an atom. He concluded that the mass of an atom was concentrated at its center. -
Millikan Oil Drop Experiment
It was the first direct and compelling measurement of the electric charge of a single electron. He was able to measure both the amount of electric force and magnitude of electric field on the tiny charge of an isolated oil droplet and from the data determine the magnitude of the charge itself. -
Niels Bohr Theory
His theory was that electrons should move around the nucleus but only in prescribed orbits.The Bohr model shows the atom as a small, positively charged nucleus surrounded by orbiting electrons. -
Henry Moseley's Advancements of the Periodic Table
He found out that his measurements of the wavelengths of the X-ray spectral lines of a number of elements which showed that the ordering of the wavelengths of the X-ray emissions of the elements coincided with the ordering of the elements by atomic number. So with the discovery of isotopes of the elements, it became apparent that atomic weight was not the significant player in the periodic law. -
Max Planck's Quantum Theory
This theory revolutionized our understanding of atomic and subatomic processes, He forced humankind to revise some of the most-cherished philosophical beliefs, and both have led to industrial and military applications that affect every aspect of modern life. -
Erwin Schrodinger “Electron Cloud Model”
He said that it consisted of a dense nucleus surrounded by a cloud of electrons at various levels in orbitals. Also he said that all matter acts as waves, and electrons themselves were wavelike. Schrodinger was correct about his atomic theory. Electrons are constantly moving and cannot be given a definite position within the atom. -
James Chadwick Atomic Theory
He bombarded beryllium atoms with alpha particles. He produced an unknown radiation. He stated that radiation was being composed of particles with a neutral electrical charge and the approximate mass of a proton. This particle became known as the neutron. -
Thomson's Model Of An Atom
He conducted an experiment to prove that rays carried a negative charge.
He stated:
-Atoms contain negatively charged particles(electrons)
-These electrons are small compared to the rest of an atom
-Thompson knew atoms are neutral, so there must be positive partials in the atom to balance the negative charge of the electrons
