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Law of Conservation of Mass
This law was discovered by Antoine Lavoisier in 1789. It stated that mass is neither created nor destroyed in any ordinary chemical reaction. In other words, the mass of substance produced by a chemical reaction is always equal to the mass of the reacting substance. -
Law of Definite Proportions
The law of definite proportions discovered by French Chemist Joseph-Louis Proust states that a chemical compound always contains exactly the same proportion of elements by mass -
Atomic Theory
John Dalton was an English chemist, his atomic theory consists of four rules; all matter is made of atoms. Atoms are indivisible and indestructible; all atoms of a given element are identical in mass and properties; compounds are formed by a combination of two or more different kinds of atoms; a chemical reaction is a rearrangement of atoms. -
Spherical Model
John Dalton was an English chemist. His Atomic Theory led him to develop the spherical atomic model of the atom. He stated that each sphere had a certain size, mass, and chemical behavior that determined what kind of element they were and that one sphere could not be broken down into smaller parts. -
Cathode Ray Tube Experiment
Michael Faraday was the first man to develop the cathode ray tube experiment; however, several people used it after him and modified it. The experiment determined that whatever produced the glow was positively charged and the magnetic field was used as evidence to support this theory. -
Electron
Richard Laming first theorized the electron in 1838. It wasn’t until 1897 where JJ Thomson made the actual discovery. He stated that the electron is a subatomic particle with a negative electric charge (e-). He also claimed that electrons were the smallest and most numerous out of the other subatomic particles. -
Quantum Theory
In 1900, Max Planck, a German theoretical physicist discovered an equation; E=Nhf, with E=energy, N=integer, h=constant, f=frequency. The amazing part of Planck's discovery was that energy, which appears to be emitted in wavelengths, is actually discharged in small packets. This new theory of energy revolutionized physics and opened the way for Albert Einstein's theory of relativity. -
Plum Pudding Model
The plum pudding model was proposed by J J Thomson, a physicist, in 1904. In this model, the pudding represented atoms filled with a positively charged fluid and the plums represented electrons that were scattered throughout the fluid. Eventually this model was proven wrong by Ernest Rutherford in 1911. -
Nuclear Model
Ernest Rutherford, who directed the famous gold foil experiment, created a new model after analyzing that the plum pudding model was incorrect. This new model, the nuclear model, contains a relatively high central charge concentrated into a very small volume, known as the nucleus. -
Nucleus
Ernest Rutherford discovered the nucleus. He found out that it consists of protons and neutrons and is located in the center of the atom. -
Gold Foil Experiment
Ernest Rutherford noticed that alpha particles would not always behave in accordance to J J Thomson’s plum pudding model when fired at a piece of gold. Rutherford directed two scientists, Geiger and Marsden where they fired a beam of alpha particles at a piece of gold foil. According to J J Thomson the particles should have passed right through the foil, however it was discovered that every 1 in 20,000 particles bounced back. -
Bohr Model
In 1913, Niels Bohr created a planetary model of an atom. In this model, the neutrons and protons occupied the nucleus while the electrons orbited around them similar to planets orbiting the sun. This model of the atomic structure is still used today. -
Proton
William Prout first came up with the idea of the proton. He beleived that it was a subatomic particle with a positive electric charge of 1(p+). Later in 1920, Ernest Rutherford named it the proton. -
Quantum Mechanical Model
Also known as the electron cloud model, the quantum mechanical model was constructed by Erwin Schrödinger. The quantum mechanical model of the atom uses complex shapes of orbitals (sometimes called electron clouds). Orbitals are volumes of space that sometimes hold electrons. This model is based on probability rather than certainty and is still used today. -
Uncertainty Principle
Werner Heisenberg was a German theoretical physicist who created the uncertainty principle. While analyzing mathematical relationships between precise position and imprecise velocity he concluded that the more precisely the position is determined, the less precisely the momentum is known in that instant and vice versa; which became known as the uncertainty principle. -
Neutron
James Chadwick discovered the neutron when he used scattering data to calculate the mass of this neutral particle.
