| A | B |
|---|
| Mendeleev | arranged known elements by atomic mass |
| Mosley | determined each element's atomic number and arranged periodic table by atomic number |
| Ekasilicon | element predicted by Mendeleev that was later discovered and named Germanium |
| Periodic Law | when arranged by atomic number there is a periodic repetition of the physical and chemical properties of the elements |
| hydrogen | element separated from all others on the periodic table |
| groups | the vertical columns on the PT; contain elements with similar physical and chemical properties |
| family | another name for group |
| periods | horizontal rows on PT; elements vary greatly |
| atomic number | number of protons |
| atomic mass | the average mass of all known isotopes of an element based on their relative abundance in nature |
| metals | left side of the zigzag staircase on the PT |
| nonmetals | elements to the right of the zigzag staircase on the PT |
| metalloids | elements on the staircase on the PT |
| luster | shininess |
| ductile | able to be drawn into a wire |
| malleable | able to be hammered into a sheet |
| corrosion | gradual wearing away of metals due to chemical reaction between metal and something in environment |
| noble gases | nonreactive elements with eight valence electrons |
| semiconductors | metalloids that become good conductors of electricity at high temperatures |
