| A | B |
|---|
| alkali metals | elements in family 1; 1 valence electrons |
| alkaline earth metals | elements in family 2; 2 valence electrons |
| atomic number | number of protons in nucleus of atom |
| mass number | sum of protons in nucleus of atom + neutrons in nucleus |
| carbon family | elements in family 14; 4 valence electrons |
| boron family | elements in family 13; 3 valence electrons |
| ductile | able to be drawn into a thin wire |
| compound | substance made of 2 or more elements chemically combined |
| 1st energy level | level closest to nucleus; holds 2 electrons |
| electrons | negatively charged particle outside nucleus of atom |
| 3rd energy level | level farthest from nucleus; holds 18 electrons |
| element | simplest type of pure substance |
| luster | shininess |
| halogens | elements in family 17; 7 valence electrons |
| malleable | able to be hammered into thin sheets |
| metals | element that is shiny, ductile, malleable; loses electrons |
| metalloids | element touching staircase in periodic table |
| non-metals | element that is dull, brittle and gains electrons |
| molecule | substance made up of 2 or more atoms chemically combined |
| neutrons | subatomic particle with no electric charge found in nucleus of atom |
| noble gases | elements in family 18; extremely unreactive |
| nitrogen family | elements in family 15; 5 valence electrons |
| oxygen family | elements in family 16; 6 valence electrons |
| periods | horizontal row of elements in periodic table (left to right) |
| subscript | number placed to lower right of chemical symbol; number of atoms |
| protons | subatomic particle with positive charge; found in nucleus of atom |
| Henry Moseley | scientist who arranged elements of modern periodic table by atomic numbers |
| Dmitri Mendeleev | scientist who first arranged elements in periodic table according to mass numbers |
| 2nd energy level | energy level that can hold 8 electrons |
| families | column of elements in periodic table (top to bottom) |
