Chemistry

Chemistry is the study of the composition, structure, properties, and reactions of matter. Matter that always has exactly the same composition is classified as a substance. Elements are the simplest substances. The smallest particle of an element is an atom.

There are only about 100 elements. In the modern periodic table, elements are arranged by increasing atomic number (number of protons). Based on their chemical and physical properties, elements are classified as metals, nonmetals, and metalloids.

Unlike physical changes, chemical changes involve a change in the composition of matter. During a reaction, chemical bonds in the reactants are broken and chemical bonds in the products are formed. Mass is conserved in chemical reactions.

Nuclear changes (such as radioactivity) involve the conversion of atoms of one element to atoms of another. During nuclear reactions, mass can be created or destroyed, and it is the total sum of mass and energy that is conserved.

Fireworks Display in ▸ Sydney, Australia When fireworks explode, they produce colorful displays of light.

Fireworks display near Sydney Opera House, Australia, with the harbour bridge in the background.
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Table of Contents

Physical Science CHAPTER 1 Science Skills CHAPTER 2 Properties of Matter CHAPTER 3 States of Matter CHAPTER 4 Atomic Structure CHAPTER 5 The Periodic Table CHAPTER 6 Chemical Bonds CHAPTER 7 Chemical Reactions CHAPTER 8 Solutions, Acids, and Bases CHAPTER 9 Carbon Chemistry CHAPTER 10 Nuclear Chemistry CHAPTER 11 Motion CHAPTER 12 Forces and Motion CHAPTER 13 Forces in Fluids CHAPTER 14 Work, Power, and Machines CHAPTER 15 Energy CHAPTER 16 Thermal Energy and Heat CHAPTER 17 Mechanical Waves and Sound CHAPTER 18 The Electromagnetic Spectrum and Light CHAPTER 19 Optics CHAPTER 20 Electricity CHAPTER 21 Magnetism CHAPTER 22 Earth's Interior CHAPTER 23 Earth's Surface CHAPTER 24 Weather and Climate CHAPTER 25 The Solar System CHAPTER 26 Exploring the Universe Skills and Reference Handbook