Unit 1 Review: Elements, Compounds, and Chemical Changes

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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 gold (Au).

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What is a compound?

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A compound is a substance formed when two or more elements chemically bond together. For example, water (H2O) is a compound made of hydrogen and oxygen.

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What is a physical change?

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A physical change is a change that affects one or more physical properties of a substance without altering its chemical composition. Examples include melting ice or crumpling paper.

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What is a chemical change?

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A chemical change is a change that results in the formation of new chemical substances. Examples include rusting iron or burning wood.

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What is a subscript in a chemical formula?

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A subscript is a small number written below and to the right of a chemical symbol in a formula, indicating the number of atoms of that element in a molecule.

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What is the smallest building block of matter?

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The smallest building block of matter is an atom. Atoms combine to form molecules and compounds.

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What is the difference between a mixture and a compound?

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A mixture is a combination of two or more substances that are not chemically bonded, while a compound is a substance formed from two or more elements that are chemically bonded.

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What happens during a chemical reaction?

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During a chemical reaction, bonds between atoms are broken and new bonds are formed, resulting in the creation of new substances.

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What is the law of conservation of mass?

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The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction; it is conserved.

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What is tarnishing?

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Tarnishing is a chemical change that occurs when a metal reacts with sulfur or oxygen in the air, forming a layer of corrosion.