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Chemistry LibreTexts

1.4: A Description of Matter

  • Page ID
    24430
  • Pure substances have an invariable composition and are composed of either elements or compounds.

    • Elements: "Substances which cannot be decomposed into simpler substances by chemical means".
    • Compounds: Can be decomposed into two or more elements.

    Elements

    Elements are the basic substances out of which all matter is composed.

    • Everything in the world is made up from only 109 different elements.
    • 90% of the human body is composed of only three elements: Oxygen, Carbon and Hydrogen

    Elements are known by common names as well as by their abbreviations. These consisting of one or two letters, with the first one capitalized. These abbreviations are derived from English or foreign words (e.g. Latin, German).

    Element

    Abbreviation

    Carbon

    C

    Fluorine

    F

    Hydrogen

    H

    Iodine

    I

    Nitrogen

    N

    Oxygen

    O

    Phosphorus

    P

    Sulfur

    S

    Aluminum

    Al

    Barium

    Ba

    Calcium

    Ca

    Chlorine

    Cl

    Helium

    He

    Magnesium

    Mg

    Platinum

    Pt

    Silicon

    Si

    Copper

    Cu (from cuprum)

    Iron

    Fe (from ferrum)

    Lead

    Pb (from plumbum)

    Mercury

    Hg (from hydrargyrum)

    Potassium

    K (from kalium)

    Silver

    Ag (from argentum)

    Sodium

    Na (from natrium)

    Tin

    Sn (from stannum)

    Compounds

    Compounds are substances of two or more elements united chemically in definite proportions by mass. For example, pure water is composed of the elements hydrogen (H) and oxygen (O) at the defined ratio of 11 % hydrogen and 89 % oxygen by mass.

    The observation that the elemental composition of a pure compound is always the same is known as the law of constant composition (or the law of definite proportions). It is credited to the French chemist Joseph Louis Proust (1754-1826).

    Contributors and Attributions

    Mike Blaber (Florida State University)


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