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400 BCE
Democritus Discovered the Atom
The greek philosopher introduced the first idea of the atom, as indestructible particles, that just float around in empty space and constantly moving. His model stated that all matter consisted of invisible particles with all different shapes and sizes. He also said that there was a void in between them, where they float around at random. -
400 BCE
Democritus Discovered the Atom
The greek philosopher was the first to introduce the idea of the atom as the most basic building block to anything with mass/matter. He said they were tiny indestructible particles that varied in sizes and shapes. His atomic model was solid and he also thought that there was a void in between them, allowing them to constantly move at random. -
John Dalton's Discoveries
Because of the new experiments with gas that became possible around the 19th century, they led John Dalton to create a modern theory of the atom based on some of his new assumptions including,
-Atoms are indestructible and invisible
-All the atoms in an element are identical
-Atoms of different elements combine in simple whole numbers to form compounds
-Atoms cannot be created or destroyed. When a compound decomposes, the atoms are recovered unchanged -
Period: to
Dmitri Mendeleev Creates the Periodic Table
Dmitri found out that if you arrange all the known chemical elements in order of increasing atomic weight, the result would be a table of a recurring pattern of properties within the groups of elements. -
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Eugen Goldstein discovers Kanalstrahlen
Kanalstrahlen, also known as canal rays or positive rays, are positively charged ions which are accelerated toward and through one of the perforated cathode in an evacuated tube. -
Period: to
J.J. Thomson Discovers the Electron
His experiments showed that all atoms contain small negatively charged subatomic particles, also known as electrons. I his experiments were done with cathode ray tubes to show the electrons. -
Period: to
Robert Millikan Discovered the Value of an Electron Charge
The concept that electricity was conveyed by a miniscule unit, also known as the electron, didn't gain much acceptance until the 1890s. Robert Millikan successfully determined the magnitude of an electron's charge by conducting an oil drop experiment. He suspended tiny, charged droplets of the oil between two metal electrons, balancing downward gravitational force, with and upward drag and other electrical forces. -
Period: to
Ernest Rutherford finds the Nucleus of an Atom
He used his Gold Foil experiment, where he demonstrated that the atom has a tiny nucleus. He created and experiment that used the alpha particles that were emitted by a radioactive element as probes to see the unseen places of the atomic structure. In his experiment he found that a screen coated with some zinc sulfide, emitted a flash of light whenever it was hit by a negative particle. He would sit in a dark room and try to count the flashes of light that were given off by the ZnS screen. -
Period: to
Niels Bohr Proposes a Theory for the Hydrogen Atom
Niel's atom model, shows it as a small positively charged nucleus, that is surrounded by orbiting electrons. He was the first to discover that the electrons float and travel in separate orbits around the nucleus. The number of electrons in the outer edge of the orbit, determines the properties of the element.