Chapter K 3 Section 2 Compounds Objectives Explain

Chapter K 3 Section 2 Compounds Objectives • Explain how elements make up compounds. • Describe the properties of compounds. • Explain how a compound can be broken down into its elements. • Give examples of common compounds. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter K 3 Section 2 Compounds: Made of Elements • A compound is a pure substance composed of two or more elements that are chemically combined. Elements combine by reacting with one another. • A particle of a compound is a called a molecule. Molecules of compounds are formed when atoms of two or more elements join together. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter K 3 Section 2 Compounds: Made of Elements • The Ratio of Elements in a Compound Elements join in a specific ratio according to their masses to form a compound. • For example, every sample of water has a 1: 8 mass ratio of hydrogen and oxygen. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter K 3 Section 2 Compounds Properties of Compounds • Each compound can be identified by its physical and chemical properties. • Properties: Compounds Versus Elements A compound has properties that differ from those of the elements that form it. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter K 3 Section 2 Compounds Breaking Down Compounds • Compounds can be broken down into their elements or into simpler compounds by chemical changes. • Methods of Breaking Down Compounds Sometimes, energy is needed for a chemical change to happen. Two ways to add energy are to apply heat and to apply an electric current. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter K 3 Section 2 Compounds in Your World • Compounds in Nature Some compounds found in nature are proteins, carbon dioxide, and carbohydrates. • Compounds in Industry Some compounds must be broken down for use in industry. Other compounds, are made in industry for use as medicines, food preservatives, and synthetic fabrics. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.