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400 BCE
Democritus
Democritus lived in Greece in 400 BC, he came up with the idea of atoms as minuscule quantities of matter that make up everything. He believed that atoms could not be destroyed, they were all different shapes and sizes, they are invisible, and there is an infinite number of them. -
400 BCE
Democritus's Atomic Model
There is little information on Democritus's experiments and hypothesis, but he envisioned atoms as the smallest particles of matter. Small, round, invisible structures. Democritus may have experimented by breaking up objects observing how they change shape. -
John Dalton
John Dalton was born in England and lived throughout the late 18th century into the 19th century. As a scientist he was interested in the atmosphere and later, using Democritus's early atomic theory, Dalton explained measures of atoms using atomic weight. He experimented with mixtures of gases and the differences between water vapor and water as a liquid and how they remained the same identity. -
John Dalton's Atomic Model
John Dalton discovered atomic weight, but still believed the atom was a singular spherical object. He believed atoms of different elements could be distinguished based on their weights, atoms couldn't be created or destroyed, atoms could combine making compound atoms, and all atoms of one element would always be the same size and weight. -
JJ Thomson's Experiments
Thomson wanted to prove that the cathode rays produced from the cathode were actually a stream of negatively charged particles called electrons. A cathode ray is a vacuum-sealed tube with a cathode and anode on one end that creates a beam of electrons travelling towards the other end of the tube. But at this time the beam of electrons was only known as the cathode ray. Thomson set up three experiments to prove that this negatively charged particle was part of the atom. -
JJ Thomson
JJ Thomson was a British physicist who discovered the electron of the atom. -
JJ Thomson's Atomic Model
Thomson's model suggested that the atom as a sphere of positive matter in which electrons were positioned by electrostatic forces. He used a plum pudding model, where the pudding was the positive matter, with plums as electrons floating around it. -
Ernest Rutherford's Experiments
Taking the previous atomic model, plum pudding, into consideration, Rutherford set up a gold foil experiment. This experiment consisted of a beam of alpha particles being shot at a sheet of gold foil. Rutherford expected the alpha particles to go straight through the gold foil, but instead some particles were deflected off of the gold and changed their path. It was later proven that because of this, there must be a positively charged nucleus in atoms, that deflected the positive alpha particles. -
Ernest Rutherford
Ernest Rutherford was a chemist and physicist, originally from New Zealand. Rutherford was a student of JJ Thomson and together they studied x-rays and were interested in the atomic structure. Rutherford did many experiments using Thomson's atomic structure theory and later proved it wrong, discovering the nucleus of the atom. -
Ernest Rutherford's Atomic Model
Rutherford's model shows the nucleus with protons and neutrons held together, orbiting the nucleus were electrons. He found that the majority of the atomic mass was from the positively charged nucleus. -
Niels Bohr
Niels Bohr was a Danish physicist and student of Ernest Rutherford. Bohr focused his work on the atom to describe electrons. He found that the previous nuclear model did not explain how certain elements can change color when they heat up. -
Bohr Model
The Bohr Model showed that electrons can only be found in specific orbits around the nucleus with fixed energy levels. Each energy level is at a set distance from the nucleus and the further away from the nucleus the more energy it has. An electron can jump from a lower orbit to a higher orbit by absorbing a certain amount of energy, heat or light. This explained why heating the elements emitted different colors. -
Erwin Schrödinger
Erwin Schrödinger was an Austrian physicist who questioned Bohr's model with mathematical equations. -
Quantum Mechanical Model
The quantum mechanical model uses quantum mathematics to describe it. Schrödinger's model unlike the Bohr model assumes that the electron is a wave and tries to describe the orbitals where electrons are most likely to be found instead of defining where they are. This model can be portrayed as a nucleus surrounded by an electron cloud. Schrödinger discovered four different types of orbitals that all overlap each other. Each orbital has multiple versions.
