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What are elements?

What are elements?. An element is a pure substance that cannot be broken down into any other substances. Each element can be identified by its specific physical and chemical properties. Each element is represented by a one- or two-letter symbol. Carbon: C Oxygen: O

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What are elements?

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  1. What are elements? • An element is a pure substance that cannot be broken down into any other substances. • Each element can be identified by its specific physical and chemical properties. • Each element is represented by a one- or two-letter symbol. • Carbon: C Oxygen: O • Hydrogen: H Aluminum: Al • Elements are made of particles called atoms. Elements have different properties because their atoms are different. 1. Apply ConceptsGive an example of a common object made from a single element.

  2. What are compounds? • Atoms can be held together by a chemical bond. Two or more atoms combined by chemical bonds may form a particle called a molecule. • A compound is a substance made of two or more elements that are chemically combined in a set ratio. Molecules of a compound are always made up of the same ratio of atoms of each element. (contd.)

  3. A chemical formula represents a compound. The numbers in a chemical formula show the ratio of atoms of each element. If there is no number, the number is assumed to be 1. • In the formula for carbon dioxide, CO2, the 2 means there are two atoms of oxygen (O) for each atom of carbon (C). • In the formula for carbon monoxide, CO, there is one atom of oxygen for each atom of carbon. • Compounds have different properties than the elements in them have. • Sulfur: yellow, powdery element • Silver: shiny, metal element • Silver sulfide (tarnish): black compound 2. IdentifyThe formula for water is H2O. How many atoms of hydrogen are there for each atom of oxygen?

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