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400 BCE
Democritus
Democritus suggested that all matter was formed of different types of tiny particles and that the properties of these particles also determined the properties of matter. It was also the first theory that explained the nature of matter being made of particles or atoms. -
330 BCE
Aristotle
Aristotle discovered the field of formal logic, and he explored relationships with scientific disciplines and how they reached to each other. -
5 BCE
Plato
Plato was a scientist who discovered that there are only five solid shapes whose sides are made from regular polygons. He was so impressed with this discovery that he was convinced that atoms of matter must have these five solids in them. -
The Alchemists
They stumbled across different substances and discovered elements such as fire, earth, water and air, and mercury, sulfur and salt. They dreamed of creating gold from lead, iron, or copper. -
Lavoisier
His discovery of the role oxygen plays in combustion, and he also discovered that air could deal with combustion. He helped make the metric system and wrote the first list of elements. He named oxygen and hydrogen. -
John Dalton
John Dalton was a chemist. He is best known for introducing the atomic theory into chemistry, and the research he founded into color blindness, which he also had. Color blindness was known as Daltonism. -
Newland’s law of octaves
Newland's law of octaves was made in 1865, he arranged the chemical elements according to their weight. The properties of every Element are a repetition of properties. -
Mendeleev's Pd. Table
Dmitri Mendeleev jotted down the symbols for the chemical elements, putting them in order according to their atomic weights and created the periodic table. The properties were later discovered and were found to be similar to his periodic table numbers. -
Photoelectric Effect
in 1887 Heinrich Rudolf Hertz discovered Photoelectric Effect. The Photoelectric Effect is electrically charged particles released from or within a material when it absorbs radiation. The effect is often defined ejection of electrons when light falls on it. -
Discovery of Radioactivity
Henri Becquerel Discovers Radioactivity. In one of the most well-known discoveries in the history of physics, on an overcast day in March 1896, Henri Becquerel opened a drawer and discovered spontaneous radioactivity. -
Discovery of the electrons
Scientist J.J Thomson, discovered electrons while working on the cathode ray in 1857. The cathode ray is something that applies electric fields towards a positively charged plate. Whie working on that he found out what electrons are during his studies. -
Discovery of protons
The proton was discovered by Ernest Rutherford in the early 1900's. During this period, resulted in a nuclear reaction which led to the 'splitting' of the atom, where he discovered protons. He named his discovery from the Greek word “protos” which means first. -
Planck's Quantum Theory of Light
Albert Einstein used Planck's quantum theory to describe the particle properties of light. It is used to describe the behavior of particles and waves at the atomic scale. -
Plum Pudding Model
The plum pudding model was first proposed by Sir Joseph John J.J. Thomson. The model tried to explain two properties of atoms he knew that electrons are negatively charged particles and that atoms have no electric charge. -
Charge of the Electrons
Robert Millikan discovered the charge of the electrons. He did it by measuring the charge of an electron using negatively charged oil droplets. He discovered it to prove the existence of electrons. -
Rutherford's Gold Foil Experiment
A piece of gold foil was hit with particles, which have a positive charge. Most particles went through it. This showed that the gold atoms were made of empty space. -
Robert Millikan
Robert Millikan discovered the charge of an electron using the oil-drop experiment. He discovered the elementary charge of an electron by measuring the course of charged water droplets in an electric field. -
Bohr's Planetary Model
a structural model of an atom. The model was proposed by physicist Niels Bohr in 1913. the electrons travel around the nucleus of an atom in the shells. The model is also referred to as the planetary model of an atom. -
Mosley's Atomic Numbers
Mosley concluded that the atomic number is the number of positive charges in the atomic nucleus, and he also concluded that there are three unknown elements with atomic numbers. Also, he discovered a relation between wave- length and atomic number. -
Schrodinger Equation
Erwin Schrödinger formulated an equation that calculated the energy levels of electrons in atoms. Schrödinger combined the equations for the behavior with another equation to generate a model of electrons in an atom. -
Heisenberg Uncertainty Principle
Uncertainty principle states that we can't know both the position and speed of a particle, such as an electron. Any object with wave-like properties will be affected by this principle in anyway. -
Discovery of the Neutron
James Chadwick fired alpha radiation at a sheet from a source. This led to the production of an uncharged radiation. He concluded that the unusually adiation consisted of uncharged particles were termed ‘neutrons.
