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430 BCE
Democritus
Democritus believed that atoms were uniform, solid, hard, incompressible, and indestructible. He also believed that they moved in infinite numbers through empty space till stopped. -
427 BCE
Plato
A Greek philosopher named Plato introduced the atomic theory which states that ideal geometric forms serve as atoms, according to which atoms broke down mathematically into triangles -
384 BCE
Aristotle
The Greek philosopher Aristotle introduced the atomic theory that there has to be something that is the source of all things. -
Lavoisier
Lavoisier believed that matter was neither created nor destroyed in chemical reactions. -
John Dalton
John Dalton's experiments with gases led him to the atomic theory that all matter is composed of extremely small particles called atoms. -
The Alchemists
The Alchemists believed that metals were formed from mercury and sulfur -
Newlands Law of Octaves
when elements are arranged in increasing order of their atomic masses. -
Mendeleev's Pd. Table
Mendeleev arranged the periodic table of elements in order of their increasing atomic weight. -
Photoelectric Effect
When electric charged particles are released from or within in a material when it absorbs electromagnetic radiation. It was discovered by Heinrich Rudolf Hertz -
Discovery of Radioactivity
Henri Becquerel Discovers Radioactivity as an accident. He opened a drawer and discovered spontaneous radioactivity. -
Discovery of the Electron
J.J. Thomson's experiments with cathode ray tubes showed that all atoms contain negatively charged particles or as they are known electrons. -
Planck's Quantum Theory
Planck's Quantum Theory states that different atoms and molecules can emit or absorb energy in discrete quantities only. -
Plum Pudding Model
The plum pudding model is a scientific model of the atom. it is defined by electrons surrounded by a volume of positive charge. it was made by J.J Thomson. -
Rutherford's Gold Foil Experiment
A piece of gold foil was hit with alpha particles, which have a positive charge. Most alpha particles went right through. This showed that the gold atoms were mostly empty space. -
Robert Millikan
Rober Millikan found the correct charge of the electron using the "falling-drop method". -
Charge of the Electron
The electron is the lightest stable subatomic particle and has a negative charge (1.602176634 × 10−19 coulomb) -
Bohr's Planetary Model
A structural model of the atom in the model the electrons travel around the nucleus of the atom in distant circular orbits or shells -
Moseley's Atomic Numbers
Henry Moseley discovered that the atomic number on periodic table is the number of positive charges in the atomic nucleus -
Discovery of the Proton
The proton was discovered by Ernest Rutherford his research resulted in a nuclear reaction which led to the first splitting of the atom, where he discovered protons. -
Schrodinger Equation
Schrodinger's Equation is a linear partial differential equation that governs the wave function of a quantum-mechanical system. -
Heisenberg Uncertainty Principle
It is a principle that states that we cannot know the position or speed of a particle accurately. It was formulated by Werner Heisenberg. -
Discovery of the Neutron
James Chadwick founded the neutron by knowing that most of the mass of an atom was in the nucleus, so he found that there was uncharged particle in the nucleus.