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400 BCE
Invention of the Atom Theory
Around 400 B.C., the Greek philosopher Democritus invented the theory that atoms exist. He said that eventually it would be impossible to break down an abject anymore, and once it got to this level it would be "unbreakable" giving these objects the name "Atome", or unbreakable. He imagined that these "Atomes" had different shapes depending on their physical characteristics. -
Dalton's Atomic Theory (the Billiard Ball model)
In the year 1803, English Chemist John Dalton came up with a study about atoms. He created four parts to his theory.
Part 1: All matter is made of atoms.
Part 2: All atoms of an element have the same properties.
Part 3: "Compounds" are made of two or more types of atoms.
Part 4: A chemical reaction starts when atoms are rearranged.
Dalton did not have any instruments in which to find and test his theory, but he used the basis of other previous theories, the laws of the conservation of mass. -
The Thomson Atomic Theory (The Plum-Pudding model)
In 1904, Chemist J.J. Thomson discovered that atoms contained negatively charged "corpuscles", or as we know them, electrons. He said that these negatively charged particles were contained within a positively charged cloud. Thomson used Cathode Ray tubes which shot a high voltage through a Cathode, a negative electrode, and an anode, a positive electrode. When charged, the Cathode ray was pulled away by the magnet, meaning it contained negatively charged particles. -
Ernest Rutherford's Atomic Theory (the Nuclear Model)
Ernest Rutherford, a physicist from New Zealand, discovered that atoms have a nucleus, or a positive charge in the center instead of it being widespread. He also discovered that atoms are made of mostly empty space. To do this he used a radioactive material in a box and pointed it at gold. He thought all the rays would travel through the gold because it was thought the positive material was a cloud, but instead some bounced off meaning the positive material was very small, but had high mass. -
Niels Bohr and the Planetary Model
In 1913, Niels Bohr created the planetary model of the atom, which basically added onto Rutherford's model. Bohr stated that the electrons moved around the nucleus like planets move around the sun. From new developments at the time, Bohr thought that maybe the electrons could only orbit the nucleus in a fixed radius, or shells. Bohr's model, even with its flaws, is widely used for teaching today to model how atoms look and bond with other atoms. -
Erwin Schrödinger and his new Quantum model
Austrian physicist Erwin Schrödinger discovered that atoms do not move in orbits, but instead in more abstract patterns. This concept was designed to find the odds of locating an electron instead of knowing where it is in relation to the nucleus. This created a new era for the discovery of the atom with a new science called quantum mechanics. -
James Chadwick's Neutron Theory (The Neutron Model)
In 1932, Englishman James Chadwick makes a groundbreaking discovery; within the nucleus, the atoms contain another particle the same mass as a proton. To find this, he shot alpha particles, a particle with two protons and two neutrons, at a sheet of beryllium. He registered an unknown radiation, not positive or negative. Since these particles had a neutral charge, he called them "neutrons". -
Period: to
Atoms Today
Nowadays, we use the model of the atom that has protons and neutrons in the nucleus, and a cloud of electrons around it. We still have developed much since the discovery of the neutron. We now know we can split an atom, and that atoms are made of even smaller particles called quarks. We know about antimatter and positrons/antielectrons. Who knows what we will discover about the atom in the future. With the developments of new technologies, who knows what future generations will know the atom as.
