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My science exam is tomorrow, I will be tested on elements mixture compound. please give...

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kwimac | Student, Grade 9 | Honors

Posted July 30, 2011 at 3:28 PM via web

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My science exam is tomorrow, I will be tested on elements mixture compound. please give me some tips and notes.

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ndnordic | High School Teacher | (Level 2) Associate Educator

Posted August 2, 2011 at 11:29 AM (Answer #1)

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All elements are pure substances that contain atoms of only one kind. These are the elements listed on the periodic table.  All elements have basically the same physical and chemical properties.

Compounds are pure substances that contain atoms of more than one kind that are chemically bonded together and cannot be separated by simple, mechanical means.  The ratio of the atoms in any compound are always in the same fixed ratio. The chemical and physical properties of compounds are always the same.  Salt is an example of a compound.

Mixtures contain two or more  pure substances that are not chemically bonded together. The pure substances can be separated into their individual components.  The physical and chemical properties of mixtures are not fixed and the ratio of the various substances can vary widely.  Salt water, sand + water, food, etc. are all examples of mixtures.

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