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450 BCE
The Greeks
In 450 B.C a greek philosopher named Empedocles said that all matter is made up of four elements in different proportions, they were earth, air, fire, and water. In 500 B.C Democritus says that matter is made up of indestructible small substances which cling together in different ways to form the objects we see around us. The Greek word for indivisible is atomos which is where the term “atom” began. -
400 BCE
The Greeks Continued
Around 400 B.C Aristotle suggested that there are pairs of options, hot and moist and,moist and dry. Possible combinations are earth (cold and dry), fire (hot and dry) etc. but he said that the balance between them creates the different atoms. After Aristotle talked about balance many thought the balance in the elements could be changed, so they could turn copper into gold. In early alchemy they would try to mix different metals to try and create gold, which was an early form of Chemistry -
Christiaan Huygens
He came up with the wave theory of light. Previously thought by Sir Isaac Newton to have been particles, Huygens deduced that it was instead waves of light. He also explained reflection and refraction. -
Issac Newton
Isaac Newton proposed a mechanical universe were solid small masses were in motion. -
John Dalton
John Dalton’s theory consisted of four statements, the first said that all matter is made up of atoms and those atoms are invisible and indestructible, the second saying all atoms of a given element are identical in mass and properties, the third said that compounds are formed by a combination of 2 or more different kinds of atoms, and the fourth saying a chemical reaction is a rearrangement of atoms. -
John Dalton Continued...
Dalton also came up with a model of the atom and that model consisted of just a tiny spherical object that is invisible and indestructible and had no internal structure. -
Gustav Kirchhoff
Kirchhoff alongside Robert Bunsen, founded spectrum analysis where they found that every element gives off a certain colour when heated to incandescence. The light given off by the element, when passing through a prism, gives off a certain wavelength that is unique to that element. This contribution to the atomic theory proved that all atoms were unique and that the things we see aren’t just made of atoms for that specific thing. -
Dmitri Mendeleev
Mendeleev arranged elements into groups with similar properties and he discovered that the properties of elements were periodic functions of their atomic weights, this became the periodic law. This was also the beginning of the periodic table -
James Maxwell
He proposed that electric and magnetic fields filled the void. Calculating the speed of electromagnetic waves, Maxwell suggesting that light is a form of electromagnetic radiation exerting pressure and carrying momentum. This provided the basis for Einstein's work on relativity from which the relationship between energy, mass and velocity contributed development of atomic energy. -
Heinrich Hertz
Hertz proved the existence of the electromagnetic waves that James Maxwell suggested. The term Hertz which represents cycles per second. -
J.J Thomson
Thomson came up with the theory of the atom’s structure looking like plum pudding which, in essence, said that the atom consists of one large positive charge and multiple negatively charged electrons held inside the atom by electrostatic forces which was later issued incorrect by Rutherford. -
Max Planck
Originated the quantum theory he stated that energy was made up of individual units, or what he called quanta. -
Ernest Rutherford
Ernest Rutherford developed the nucleus. He conducted an experiment we know as the gold foil experiment. He showed that the atom had a small and heavy nucleus. He decided to shoot alpha particles into a piece of gold foil, when he did this some of the particles were deflected because of that he concluded that a tiny nucleus was causing the deflections.He developed his own diagram that had a nucleus and orbitals around that the electrons moved on.https://www.youtube.com/watch?v=XBqHkraf8iE -
Niels Bohr
Niels Bohr proposed a model that showed the atom with a small positively charged nucleus that is surrounded by the orbiting electrons. He was the first to discover that electrons move on these orbitals and are able to move freely between the orbits if they have the right amounts of energy. -
Albert Einstein
Albert Einstein released the theory of relativity which became the basis for the release of atomic energy. -
Erwin Schrodinger
Erwin suggested that the electrons behaved like waves. He used equations to explain the probability of finding an electron in a certain position. This atomic model is known as the quantum mechanical model of the atom and the most accurate we see today -
Heisenberg
Heisenberg described atoms in a formula that was connected to the frequency of spectral lines. Heisenberg also proposed the Uncertainty Principle which is you cannot know both the position and velocity of a particle, which may have helped develop the cloud model where the electron location is based on probability. -
James Chadwick
Chadwick made use of alpha particles to discover the neutral atomic particle that had a mass close to the proton. The was how the neutron was discovered.
