| A | B |
|---|
| neutron | neutral subatomic particle, located inside the nucleus |
| proton | postively charged subatomic particle, located inside the nucleus |
| electron | negatively charged subatomic particle, located in orbits around the nucleus |
| nucleus | center of an atom, contains the protons and neutrons |
| Democritus | 400 BC, proposed that elements are made of tiny solid particles that cannot be subdivided (uncuttable) named them atomos |
| John Dalton | 1808, developed an atomic theory (chemicals made of atoms, atoms of elements are identical in mass (later proven wrong), atoms of different elements have different masses, atoms combine in small whole number ratios) |
| JJ Thompson | 1904, proved that atoms have a negatively charged particle (the electron) using a cathode ray tube |
| Ernest Rutherford | 1911, proposed the theory that all the mass and the positive charge of an atom is in center and is surrounded by electrons in mostly empty space |
| Neils Bohr | 1913, hypothesized that electrons were in fixed orbits around the nucleus, came up with the idea of energy levels |
| Modern Model of the Atom | Electrons are located in the cloud in levels depending on their energy |
| Atomic Number | the number of protons an atom has (distinct for each element) |
| Atomic Mass | the sum of the protons and neutrons of an atom |
| isotope | an atom of an element that has a different number of NEUTRONS |
| Dimitri Mendeleev | developed the first periodic table of the elements, arranged by atomic mass |
| Henry Mosely | arranged the periodic table by increasing atomic number, this is still in use today |
| Metals | left side of the periodic table in blue |
| Metalloids | middle stairstep in green, have properties of both metals and non-metals |
| Non-Metals | right side of the periodic table in yellow |
| electron dot diagram | shows the number of valence electrons (electrons in outer shell) |
| noble gases | far right of periodic table - all have 8 electrons in the outer shell |
