Elements, Compounds and Mixtures

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What is an element?

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

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What is a compound?

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A substance formed when two or more different elements are chemically bonded together. Examples include water (H2O) and carbon dioxide (CO2).

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What is a mixture?

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A combination of two or more substances that are not chemically bonded. Examples include air (a mixture of gases) and salad (a mixture of vegetables).

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What is a molecule?

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The smallest unit of a chemical compound that retains its chemical properties, consisting of two or more atoms bonded together. For example, O2 is a molecule of oxygen.

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What is the difference between an element and a compound?

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An element is a pure substance made of one type of atom, while a compound is made of two or more different types of atoms chemically bonded together.

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What is a homogeneous mixture?

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A mixture that has a uniform composition throughout, such as saltwater or air.

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What is a heterogeneous mixture?

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A mixture that does not have a uniform composition and the different components can be seen, such as a salad or a mixture of sand and iron filings.

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What is a solution?

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A homogeneous mixture where one substance (the solute) is dissolved in another (the solvent), such as sugar in water.

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What is the law of conservation of mass?

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A principle stating that mass is neither created nor destroyed in a chemical reaction; the total mass of reactants equals the total mass of products.

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What is a physical change?

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A change that affects one or more physical properties of a substance without altering its chemical composition, such as melting ice.