Organization of the periodic table
The periodic table lists the elements in order of atomic number. Its shape puts elements with similar behavior in the same column.
- A period is a row. Elements in a period have the same number of occupied energy levels.
- A group is a column. Elements in a group have the same number of valence electrons, so they react in similar ways.
Important groups:
| Group | Name | Behavior |
|---|---|---|
| 1 | Alkali metals | Very reactive metals, form 1+ ions |
| 2 | Alkaline earth metals | Reactive metals, form 2+ ions |
| 17 | Halogens | Very reactive nonmetals, form 1- ions |
| 18 | Noble gases | Almost unreactive |
Metals are on the left and center. They are shiny, conduct electricity and lose electrons. Nonmetals are on the upper right. Metalloids along the dividing staircase have properties of both.
Worked example: locate sulfur
Sulfur has atomic number 16 and the configuration 1s2 2s2 2p6 3s2 3p4.
- Its highest energy level is 3, so it is in period 3.
- It has 6 valence electrons, so it is in group 16.
- It sits on the right side, so it is a nonmetal.
Common mistake
Mixing up groups and periods. Groups go down, like columns holding up a building. Periods go across, like a sentence that ends in a period.