1. Chapter Four
The Periodic Table

2. 4.1 Organizing the Elements
Atomic Mass- the average mass of an element; how much an element weighs
Dmitri Mendeleev-Russian scientist-organized elements in order of increasing atomic mass
Periodic Law States: if the elements are arranged according to their atomic mass, a pattern can be seen in which similar properties occur regularly.

3. 4.4 Groups of Elements
Chemical group- the set of elements in the same column
They have similar physical and chemical properties
1)Noble Gases-Group 18
Inert gases because they are unreactive; they almost never form chemical compounds with other elements

4. Uses; helium-lighter than air blimps
Neon-colorful light displays, argon-fill light bulbs
Their outer orbits are “filled”; stable arrangement of electrons
2) Alkali Metals-Group 1; they are all shiny, silvery, metals
They are extremely reactive

5. They are found in nature only as compounds
Common ones: sodium compounds found in plants, animals, soil and sea water
Sodium hydroxide; used in making soap and paper
Electron arrangement is unstable, only one electron on outer shell

6. 3) Halogens-Group 17; are the most reactive nonmetals
They appear naturally as compounds in nature not elements
Most common are chlorine compounds found in living things, ocean water, and rocks.
Electronic structure-seven electrons on outer shell

7. Hydrogen is a unique element
It is colorless, odorless, tasteless, highly flammable gas
Acts like a metal and nonmetal
One of the main elements in all living things, as well as petroleum, coal and natural gas.