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Democritus
Democritus, from Greece, had a theory that everything made up of atoms. He believed these atoms were physically, not geometrically, indivisible, and so he called them "atom". He believed that between atoms lies empty space, that atoms are indestructible -
Law of Conservation of Mass
The Law of Conservation of Mass founded by Antoine Lavoisier in 1789. He discovered that mass is neither created nor destroyed in chemical reactions. In other words, the mass of any one element at the beginning of a reaction will equal the mass of that element at the end of the reaction -
Law of definite proportions
The law of definite proportions states that a chemical compound always contains exactly the same proportion of elements by mass. -
Atomic Theory
Atomic theory is the several theories describing the structure, behavior, and other properties of the atom. -
John Dalton
English chemist who proposed the Atomic Theory which stated that all matter was composed of small indivisible particles called atoms. These atoms possess unique characteristics and weight for different elements. He also stated that three types of atoms exist: simple, compound, and complex. -
Joseph Proust
He was a French chemist who proved substances combine in proportions, also known as Proust's law or the law of definite proportions. -
James Clerk Maxwell
His biggest acheivement was coming up with electromagnetic theory. This united all unrelated observations, experiments and equations of electricity, magnetism and optics into one theory. -
Henri Becquerel
Henry Becquerel was a French physicist who found that rays coming from a uranium affected a photographic plate. The rays were not from an outside source and were more powerful than a sample of pure uranium. His experiment led to the discovery of natural radioactivity. -
Plum Pudding Model
proposed by J.J Thompson it was the first to show electrons, but it excluded the nucleus -
Electron
The discovery of the electron came out of curiosity when J.J Thomson was conducting an experiment which involved a ray of electricity being passed through a vacuum tube. A light would appear because of this and it was Thomson who discovered that it would bend slightly towards a positively charged plate. As a result of this the negatively charged electron was discovered. -
Cathode Ray Tube Experiment
J.J. conducted the Cathode Ray experiment 3 times before he found out that the charge to mass ratio was so large that the particles either carried a huge charge, or were a thousand times smaller than a hydrogen ion. He then came up with the idea that the cathode rays were made of particles that came from within the atoms themselves. -
Quantum theory
Quantum theory is the basis of modern physics that explains the nature and behavior of matter and energy on the atomic and subatomic level. -
Max Planck
Max Planck was a German physicist who founded the quantum theory. Quantum theory is about the nature of matter and it's properties. -
Robert Millikan
Millikan measured the charge on an electron with his oil-drop experiments.He then successfully measured the charge and mass of an electron. He also proved that this was a constant for all electrons. -
Nuclear Model
Proposed by Ernest Rutherford in 1911, it described the atom as a tiny positively charged core called a nucleus which is where all the mass concentrated around. The electrons cirulate at distance around the nucleus. -
Ruherford'sGold Foil Experiment
Ernest Rutherford's experiment of shooting alpha particles through a thin sheet of gold, and discovering that some were deflected, proved that an atom is actually a small dense nucleus surrounded by orbiting electrons. -
Ernest Rutherford
Said to be the central figure in the study of radioactivity Inferred the positive charge of nucleus due to his gold foil experiment. He also attended Cambridge University and won the Noble Prize in Chemistry. -
Proton
In 1911 Ernest Rutherford performed many experiments to explore radioactivity did an experiment in where he discovered that the atom must have a positive center that contains most of the atom's mass.
He suggested that the nucleus contained a particle with a positive charge the proton. -
Nucleus
The nucleus is the very dense region of the atom consisting of protons and neutrons. It was discovered in 1911 as a result of Ernest Rutherford's interpretation of the gold foil experiment. -
Johannes Wilhelm Geiger
German physicist who introduced the first successful detector of alpha particles and other radiations. -
Bohr Model
This model proposed that electrons could only
orbit the nucleus in larger orbits around the
nucleus. The outer orbits could hold more electrons. The
electrons in the outermost shell determine the properties of
the atom. -
Neils Bohr
A Danish physicist who attended the University of Copenhagen in 1911 and made large contributions to the atomic structure and quantum theory. -
Quantum Mechanical Model
The quantum mechanical model was constructed by Erwin Schrödinger.In this, electrons are defined as standing waves. The electron distribution shows areas where the probability of electron's locations are high. The exact location of the electron is never known. -
Werner Karl Heisenberg
Made contributions to quantum mechanics and is best known for the uncertainty principle of quantum theory. Also, he made important contributions to nuclear physics. -
James Chadwick
Chadwick discovered the third sub-atomic partical, He named it the ‘neutron’. Nuetrons help stabilise the protons in the atom’s nucleus, preventing the protons from repelling each other. -
Neutron
James Chadwick, an English physicist who had worked with Rutherford, detected neutrons and measured their mass in an invisible game of billiards. Some of the neutrons collided with protons in the wax and knocked them out.Using his knowledge of energy and momentum, he was able to work out the mass. -
Modern Atomic Model
Electrons are in constant motion around the nucleus, protons and neutrons vibrate within the nucleus,
