| A | B |
|---|
| Democritus | 440 BCE. Thought that if you keep cutting something up you would end up with a particle that could not be cut. He named this the “atomos” meaning “not able to be divided” |
| Dalton - 1803 | all substances are made of atoms. Atoms are small particles that cannot be created, divided or destroyed |
| J.J Thomson – 1897. | Used the cathode-ray tube |
| Ernest Rutherford – 1909. | Gold foil experiment – he shot positively charged particles at gold foil,• Atoms are mostly empty space |
| Niels Bohr – 1913 | Electrons move about in certain paths or energy levels |
| Schrodinger & Heisenberg - Early 1900s (20th Century) | Electron Cloud model – electrons are not found in exact orbits but there are regions where they are likely to be found, these regions are electron clouds |
| Neutral Atom | Has the same number of protons and electrons |
| isotopes | Atoms of an element with different # of neutrons |
| The number of protons is always the same in the same element, however, the number of neutrons may be different in that element | isotopes |
| Groups or Families | Colums, verticle, elements in the same group often have similar chemical and physical properties |
| Periods | Rows or horizontal The physical and chemical properties of elements in a row follow a repeating OR periodic pattern. |
| Amu | atomic mass unit |
| Nobel gases | do not normally form compounds |
| Periodic | “happening at regular intervals”. |
| Alkali Metal | the most reactive elements are in this group |
| Alkali –Earth metal | not as reactive as alkali metals |
| Halogens | very reactive nonmetals. Poor conductors of electric current, violent reactions with alkali metals to form salts; never in uncombined form in nature |
| Periodic Law | repeating or chemical and physical properties of elements change periodically with the element’s atomic number |
| Metals | Shiny, Malleable, Ductile, Good conductors of thermal energy |
| Nonmetals | Not malleable or ductile – they are brittle and will shatter or break when hit |
| Metalloids | Have some properties of metals and nonmetals, shiny |
| Atoms had tiny extremely, dense, positively charged center (nucleus) | Rutherford - 1909 |
| atoms of the same element are exactly alike and the atoms of different elements are different, atoms join w/other atoms to make new substances | Dalton - 1803 |
| "Plum Pudding" model - discovered electrons | J.J. Thomson - 1897 |
