Periodic Table of Science | Print |

Periodic Table

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Periodic Table Notes
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Atomic Number - An element is defined by the number of protons it has. Carbon atoms have six protons, hydrogen atoms have one proton and oxygen atoms have eight protons. The number of protons an atom has is called the atomic number. The chemical behavior of an element depends on the number of protons in an atom.

Atomic Symbol - These are almost always one or two letters that represent an element. They're used worldwide and usually relate to the name of the element or the Latin name of the element. An example of this is "O" for Oxygen and "Ca" for Calcium.

Atomic Mass - The average mass of an element in atomic mass units (amu.) The mass in an atom is so small that we use amu. That's about the mass of one proton or neutron. The atomic mass is a decimal number on the Periodic Table because it's an average of the various isotopes (one or more atoms that have the same atomic number but different mass numbers) of an element. To find the average number of neutrons for an element, simply subtract the number of protons (atomic number) from that atomic mass.

Long before anyone knew any detail about the atoms or any of the periodic properties the elements were divided into two broad categories
---> metals and non-metals.

Alkali Metals - These are group one in the periodic table. They don't occur freely in nature and are softer than most metals. Like all metals, they are great heat conductors and can even explode if exposed to water.

Alkaline Earth Metals - These are group two in the periodic table. Because they're extremely reactive, they aren't found freely in nature. An example of an alkaline earth metal is radium.

Transition Metals - The 38 elements in groups three to 12 are called transition metals. Three interesting elements in this group are iron, cobalt and nickel. They're the only elements known that produce a magnetic field.

Other Metals - There are seven elements considered "other metals" in groups 13 to 15. All these elements are solid with a high density. Examples of them are tin, aluminum and lead.

Metalliods - These elements have both metal and non-metal properties. Some of them are semi-conductors, which means they can carry an electrical charge under special conditions. Metalloids are great for computers and calculators.

Non-Metals - These fall into groups 14 to 16 in the periodic table. They can't conduct heat or electricity very well and are brittle. They also can't be made into wire or sheets. At room temperature, non-metals turn into gasses and solids.

Halogens - All five halogens are non-metallic elements. "Halogen" means "salt former" so compounds that contain halogen are called "salts." At room temperature, they are in three states of matter: solid, liquid and gas.

Noble Gases - The six noble gases are in group 18. All of them have the maximum number of electrons possible in their outer shell which makes them stable. Examples of noble gases are helium, neon and krypton.

Rare Earth Elements - There are 30 rare earth elements. Many of them are synthetic or man-made. They're found in group three of the periodic table and the sixth and seventh groups.