Here is a detailed HTML document for "Chapter 13: Organic Chemistry I (Hydrocarbons)," covering carbon chains, alkanes, alkenes, alkynes, and isomerism, complete with extensive explanations and practice questions. ```html

13.0 ORGANIC CHEMISTRY I (HYDROCARBONS)

Organic chemistry is the study of carbon-based compounds. Carbon is unique because it can form long chains and rings, leading to millions of different substances – from fuels and plastics to medicines and DNA. This chapter introduces the simplest organic compounds: hydrocarbons, which contain only carbon and hydrogen. We explore the three main families: alkanes (single bonds), alkenes (double bonds), and alkynes (triple bonds), along with the concept of isomerism.

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13.1 INTRODUCTION TO CARBON CHAINS

Carbon atoms can bond with each other to form chains and rings because each carbon atom has four valence electrons and can form four strong covalent bonds. This property is called catenation.

• Carbon always forms 4 covalent bonds.
• Chains can be straight, branched, or cyclic.
• The same set of atoms can be arranged in different ways, leading to isomers.

Hydrocarbons are divided into two main classes:

• Saturated hydrocarbons: Contain only single bonds (C–C). They are called alkanes.
• Unsaturated hydrocarbons: Contain at least one double (C=C) or triple (C≡C) bond. They are called alkenes (double) and alkynes (triple).
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