| Term | Definition |
|---|
| Atom | the smallest unit of an element that maintains the prpopertier of that element |
| electrons | a subtomic particle that has a negative charge |
| nucleus | an atom's central region, which if made up of protons and neutrons |
| electron cloud | a region around the nucleus of an atom where electrons are likely to be found |
| proton | a subatomic particle that has a positive charge and that is located in the nucleus of an atom |
| atomic mass unit (amu) | a unit of mass that describes the mass of an atom or a molecule |
| neutron | a subtomic particle that has no charge and that is located in the nucleus of an atom |
| atomic number | the number of protons in the nucleus of an atom; is the same for all atoms of the element |
| isotope | an atom that has the same number of protons (or the same atomic number) as other atoms of the same element do but that has a different number of neutrons (and thus a different atomic mass) |
| mass number | tha sum of numers of protons and neutrons in the nucleus of an atom |
| atomic mass | the mass of an atom expressed in atomic mass units |
| Gravitational force | pulls objects toward one another however in an atom because the mass of the particles is so small the force within atoms is very small |
| electromagnetic force | holds the electrons around the nucleus; makes opposite charges attract and like charges repel |
| Strong force | holds two protons in a nucleus together using nutrons; the force is greater then the electromagnetic force causing the protons to stay together |
| weak force | plays a key role when a neutron changes into a proton or an eletron in ratioactive atoms |
| Democritus | 440BC imagined all matter to be made of particles which he called "atoms" |
| Joseph Priestly | (1733-1804) discovered oxygen and made soda pop |
| Henery Cavendish | (1731-1810) discovered hydrogen and that water is a ompound of hydrogen and oxygen. He measured the universal gravitational constant |
| Antoine Louisier | (1743-1791) explained combustion (burning) |
| John Dolton | (1766-1844) realized that elements combined in simple whole numbers ratuis |
| Dmitri Mendeleau | (1834-1907) developed the penodic table of elements and predicted missing elements and their properties |
| Willhelm Roetgen | (1845-1923) discovered xrays |
| Henri Becquerel | (1852-1908) experimented with radio active substances |
| Marrie and Pierre Currie | isolated radium and polonium |
| William Crooke | (1832-1919) showed that "cathode rays" (electrons) have difficulted by a magnet |
| JJ Thomson (1856-1940) | named the cathode rays "electrons" and realized they come from atoms. He imagined the electrons like plum in a pudding |
| Earnest Rutherford (1871-1937) | showed that atoms have a tiny positive nucleus with his "gold foil" experiment |
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