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History of the Atom
| Term | Definition |
|---|---|
| Atomic number | Equal to the number of protons |
| Mass number | Equal to the number of protons + number of neutrons |
| Protons | Positively charged particles located in the nucleus, responsible for the identity of the atom |
| Neutrons | A subatomic particle that has no charge and that is found in the nucleus of an atom; responsible for the stability of the nucleus |
| Electrons | Negatively charge particles located in the electron cloud, responsible for chemical properties |
| Nucleus | Located at the center of the atom, holds the protons and the neutrons |
| Valence electrons | Located at the center of the atom, holds the protons and the neutrons |
| Atomic mass | Total weight of protons and neutrons |
| Atom | Smallest unit of matter |
| Periodic Table | A chart of the elements showing the repeating pattern of their properties |
| Democritus | Named the atom after the Greek word "atomos" which means indivisible; believed there is a limit to how many times one can break matter into smaller pieces; eventually one reaches the smallest particle. |
| Artistotle | All matter is composed of fire, water, earth, and air. Founder of alchemy. |
| John Dalton | All matter made of atoms; all atoms of an element are alike, but are different from other elements; elements can be combined to make compounds; chemical reactions are a rearrangement of elements, but do not change the elements themselves. |
| JJ Thomson | Discovers the electron of an atom using a cathode ray tube; also said the electron must be balanced by positive charge; found that cathode rays could be bent by both electric fields and magnetic fields |
| Ernest Rutherford | Performed the gold foil experiment; proved that most of the atom is empty space and the existence of the positive nucleus at its center; discovered the proton and the nucleus |
| James Chadwick | Discovered the neutron and that its mass is the same as the proton |
| Niels Bohr | Electrons should move around the nucleus but only in prescribed orbits |
| Dalton's model of the atom | Billiard Ball model; Indivisible, indestructible, solid sphere |
| Thomson's model of the atom | Plum-pudding model; Positive charge spread over the sphere with negatively charged electrons inside |
| Rutherford's model of the atom | Nuclear model; A tiny nucleus (positive charge) around which electrons (negative) orbit |
| Bohr's model of the atom | Planetary model; The electrons orbit nucleus at discreet orbits which correspond to energy levels |
| Schrodinger's model of the atom | Quantum model; it is impossible to know the exact location of the electrons instead we have "clouds of probability" called orbitals in which we are more likely to find an electron |
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maske_steph
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