Elements, Compounds, and Mixtures

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What is an element?

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An element is a pure substance that cannot be broken down into simpler substances by chemical means. Examples include hydrogen (H), oxygen (O), and carbon (C).

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What is a compound?

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A compound is a substance formed when two or more elements are chemically bonded together. Examples include water (H2O) and ammonia (NH3).

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What is a mixture?

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A mixture is a combination of two or more substances that are not chemically bonded. Mixtures can be homogeneous (uniform composition) or heterogeneous (distinct, separate components).

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What is the difference between a homogeneous mixture and a heterogeneous mixture?

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A homogeneous mixture has a uniform composition throughout, while a heterogeneous mixture has visibly different substances or phases. Example: Saltwater (homogeneous) vs. salad (heterogeneous).

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What is a molecule?

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A molecule is the smallest unit of a chemical compound that retains its chemical properties. It consists of two or more atoms bonded together. Example: A water molecule (H2O) consists of two hydrogen atoms and one oxygen atom.

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What is the chemical formula for table salt?

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The chemical formula for table salt is NaCl, which indicates it is a compound made of sodium (Na) and chlorine (Cl) ions.

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What does the chemical formula C12H22O11 represent?

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The chemical formula C12H22O11 represents sucrose, which is a compound (sugar) made of carbon, hydrogen, and oxygen.

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What is the significance of the subscript in a chemical formula?

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The subscript in a chemical formula indicates the number of atoms of each element in a molecule. For example, in H2O, the '2' indicates there are two hydrogen atoms.

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What is a pure substance?

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A pure substance is a material that has a constant composition and consistent properties throughout. It can be an element or a compound.

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What is the difference between an atom and a molecule?

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An atom is the smallest unit of an element, while a molecule is a group of two or more atoms bonded together. For example, a single oxygen atom (O) is an atom, while O2 is a molecule.