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| 11100490895 | Group 1 | Alkali metals. |  | 0 |
| 11100490896 | Group 2 | Alkaline earth metals | | 1 |
| 11100490897 | Groups 3-12 | transition metals | | 2 |
| 11100490898 | metalloids | Found along the 'staircase'. Have properties of both metals and nonmetals |  | 3 |
| 11100490899 | nonmetals | brittle , dull, poor conductors of heat and electricity |  | 4 |
| 11100490900 | Proton | Positively charged particle in the nucleus of an atom |  | 5 |
| 11100490901 | Neutron | A subatomic particle that is neutral and that is found in the nucleus of an atom |  | 6 |
| 11100490902 | Electron | A tiny, negatively charged particle that moves around the nucleus of an atom. |  | 7 |
| 11100490903 | Atomic Number | The number of protons in the nucleus of an atom of an element |  | 8 |
| 11100490904 | Mass Number | The total number of protons and neutrons in an atom's nucleus |  | 9 |
| 11100490905 | Periodic table | A chart of all chemical elements currently known, organized by their properties. |  | 10 |
| 11100490906 | Element | pure substance that consists entirely of one type of atom |  | 11 |
| 11100490907 | atom | the smallest unit of an element that maintains the properties of that element |  | 12 |
| 11100490908 | periods | horizontal rows on the periodic table |  | 13 |
| 11100490909 | groups | vertical columns on the periodic table that have common properties |  | 14 |
| 11100490910 | metal | shiny, malleable, ductile and good conductors |  | 15 |
| 11100490911 | malleable | able to be hammered into thin sheets |  | 16 |
| 11100490912 | ductile | can be pulled into long wires |  | 17 |
| 11100490913 | conductivity | the ability of an object to transfer heat or electricity to another object |  | 18 |
| 11100490915 | alkali metals | very reactive, not found alone in nature, react violently with water |  | 19 |
| 11100490916 | alkaline earth metals | hard, grey-white, good conductors of electricity, calcium and magnesium are examples |  | 20 |
| 11100490917 | Transition metals | most are hard and shiny, less reactive, examples are iron, copper, nickel and gold |  | 21 |
| 11100490918 | lanthanides | the first period below the periodic table, they are mixed with more common metals to form alloys |  | 22 |
| 11100490919 | alloy | a mixture of a metal with at least one other element- strengthens the structure |  | 23 |
| 11100490920 | actinides | the period below lanthanides, very unstable |  | 24 |
| 11100490921 | synthetic elements | not found naturally on earth, all elements higher than 92 |  | 25 |
| 11100490922 | Thomson | discovered the electron | 26 | |
| 11100490923 | Bohr | discovered that electrons follow an orbit/shell | 27 | |
| 11100490924 | Chadwick | discovered the neutron | 28 | |
| 11100490925 | Rutherford | discovered the proton with the gold foil experiment | 29 | |
| 11100490926 | Dalton' | 1. elements are made from tiny particles called atoms. 2. all atoms of a given element are identical 3.atoms cannot be subdivided, created or destroyed. 4. atoms combine in simple whole number ratios to form compounds 5. in chemical reactions, atoms are rearranged | 30 | |
| 11100490929 | Ion | forms when an atom loses or gains an electron | 31 | |
| 11100490930 | Isotope | the protons remain the same as the atomic number, but the neutrons do not | 32 | |
| 11100490931 | Mendeleev | Created the first periodic table. Arranged elements by increasing atomic mass. Left gaps for undiscovered elements | 33 | |
| 11100490932 | Noble gases | elements in group 18 that have complete outer shells | 34 | |
| 11100562985 | Democritus | Greek philosopher that said all matter is made of tiny particles called "atomos" or atoms | 35 | |
| 11100719038 | Antoine Lavoisier | made the earliest attempt to classify the elements and he did so by their properties | 36 | |
| 11100729090 | Johann Dobereiner | he recognized triads of elements with similar properties and showed that properties of the middle element could be predicted from the other two | 37 | |
| 11100756937 | John Newlands | He proposed the Law of Octaves in grouping the elements, in which they were arranged by similarities between elements with atomic weights that differed 7. However he did not leave room for new elements and even put 2 elements in one box. | 38 | |
| 11100791922 | Henry Moseley | Arranged the periodic table by atomic number instead of mass number, which is what we use today | 39 |
