Chapter Four The Periodic Table

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.

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

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

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

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

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.