| A | B |
|---|
| Mendeleev | first person to arrange the periodic table by properties and mass |
| Periodic Law | properties of elements that repeat in predictable ways due to atomic number of each element |
| periods | row across in periodic table |
| group | families or columns down in PT; similar properties |
| atomic mass unit | weighted average of all isotopes(differing neutrons) of an element; atomic mass |
| elements classifiction | metals,nonmetals and metalloid |
| metals | elements conduct electricity and heat; solids at room temperature |
| transition metals | groups 3-12 |
| nonmetals | poor conductors of electricity and heat;most gases at room temperature |
| metalloids | elements with properties that fall between metals and nonmetals |
| why a group with similar properties? | all have same number of valence (outer circle) electrons |
| Group 1a -extremely reactive metals ex. Na- sodium | alkali metals |
| valence electrons | electrons on outer orbit of atom; they react with other electrons to form compounds |
| reactive metals; 2 valence electrons ex. Ca-calcium | alkali earth metals |
| halogens | highly reactive nonmetals; group 7; ex.Cl-chlorine |
| noble gases | nonreactive odorless colorless gases |
| oxygen | group 6 most abundant element in the earth's crust |
| aluminum | group 3 element-most abundant metal in the earth's crust |
| isotopes | neucleus of same atoms with differing neutrons |
