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PERIODIC TABLE
Lesson 1 - Page 2

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The periodic table of today lists every single element known on Earth.  They are placed in order of their atomic number (number of protons).  The atomic weigh or more correctly the atomic mass, helps to predict the properties of different elements.  The concept of atomic weight has changed through time depending on how the number was obtained by various scientists.  Since 1960 the value has been standardized by chemists, who determine the number using different analytic and mathematical tools.  Today the atomic weight should be referred to as the atomic mass and the unit of measurement is called atomic mass unit (amu). 

Each box on the Periodic Table of the Elements includes at a minimum, the atomic number, atomic symbol, and atomic mass.  Larger charts can show many other features using a variety of colors and symbols that help define physical properties.  These properties could include boiling points, melting point, density, and crystal structure.  Today’s periodic tables vary depending on who may use the table. 

The boxes on the Periodic Table are arranged as a data chart so we can derive information not only on an individual element but how the elements relate to each other.  The horizontal rows are divided into “periods” (1-7) and the vertical columns are divided into “groups.” The groups have two designations 1-18 (new) and 1A-8A;1B-8B (older).   However, many chemists still use the number and letter designation.


 

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