1. ELEMENTS

2. Elements pure substance that cannot be separated into simpler substance by physical or chemical means. 1

3. Elements Science has come along way since Aristotle’s theory of Air, Water, Fire, and Earth. Scientists have identified 90 naturally occurring elements, and created about 28 others. 2

4. Elements All elements are made of atoms. Atoms of the same element are alike. Atoms of different elements are different. 3

5. Elements In 1813, a system of representing elements with symbols was introduced. Each symbol consists of one or two letters. Two letters are needed for a chemical symbol when the first letter of that element’s name has already been used. 4

6. Periodic Table of Elements pure substances that cannot be separated into simpler substance by physical or chemical means. Each block is a different Element. 5

7. Mendeleev In 1869, Dmitri Ivanovitch Mendeléev created the first accepted version of the periodic table. He grouped elements according to their atomic mass, and as he did, he found that the families had similar chemical properties. Blank spaces were left open to add the new elements he predicted would occur. 6

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