| A | B |
|---|
| alkali metals | elements in family 1 that have one valence electron |
| alkaline earth metals | elements in family 2 that have two valence electrons |
| mass number | the sum of the protons and neutrons in the nucleus of an atom |
| atomic number | the number of protons in the nucleus of an atom |
| boron family | elements in family 13 that have three valence electrons |
| carbon family | elements in family 14 that have four valence electrons |
| compound | substance made of two or more elements chemically combined |
| ductile | able to be drawn into a thin wire |
| electron | negatively charged particle found outside the nucleus of an atom |
| first energy level | level found closest to the nucleus that holds two electrons |
| second energy level | level that can hold 8 electrons |
| third energy level | level farthest from the nucleus that can hold 18 electrons |
| element | simplest type of pure substance |
| family | column of elements in the periodic table (goes from top to bottom) |
| halogen family | elements in family 17 that have seven valence electrons |
| luster | shininess |
| malleable | able to be hammered into a thin sheet |
| metal | element that is shiny, ductile and malleable, and tends to lose valence electrons |
| nonmetal | element that is dull, brittle, and tends to gain valence electrons |
| metalloid | element found touching the staircase on the periodic table |
| molecule | substance made up of two or more atoms chemically combined |
| neutron | subatomic particle with no electric charge that is found in the nucleus of an atom |
| nitrogen family | elements in family 15 that have five valence electrons |
| noble gases | elements in family 18 that are extremely unreactive |
| oxygen family | elements in family 16 that have six valence electrons |
| period | horizontal row of elements in the periodic table (left to right) |
| proton | subatomic particle that has a positive charge and is found in the nucleus of an atom |
| subscript | number placed to the lower right of a chemical symbol that tells the number of atoms of the element in the compound |
| Dmitri Mendeleev | scientist who first arranged the elements of the periodic table according to their increasing mass numbers |
| Henry Moseley | scientist who arranged the elements of the modern day periodic table by their increasing atomic numbers |
