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1 Chapter 8 Covalent Bonding 8.1 What information does a molecular formula provide? 8.2 The Nature of Covalent Bonding 8.3 Bonding Theories 8.4 Polar Bonds and Molecules 1 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. 2 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. In nature, only the noble gas elements, such as helium and neon, exist as uncombined atoms. Monatomic molecules But not all elements are monatomic. O 2 represents two oxygen atoms that are bonded together. What are the 7 diatomic molecules? 3 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. 4 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. 1

2 Ionic compounds are generally crystalline solids with high melting points. Molecular compounds, however, have very different properties. Water (H 2 O) is a liquid at room temperature. Carbon dioxide (CO 2 ) and nitrous oxide (N 2 O) are both gases at room temperature. The attractions that hold together the atoms in O 2, H 2 O, CO 2, and N 2 O are not ionic bonds. do not involve the transfer of electrons. 5 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. 6 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. Sharing Electrons Molecular compounds combine by sharing electrons. covalent bond Sharing Electrons A molecule is a neutral group of atoms joined together by covalent bonds. Oxygen gas consists of oxygen molecules; each oxygen molecule consists of two covalently bonded oxygen atoms. 7 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. 8 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. 2

3 A molecular formula shows how many atoms of each element a substance contains. The molecular formula of water is H 2 O. The subscript after an element s symbol indicates the number of atoms of each element in the molecule. the subscript 1 is omitted. 9 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. 10 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. Butane is also a molecular compound. The molecular formula for butane is C 4 H 10. One molecule of butane contains four carbon atoms and ten hydrogen atoms. A molecular formula reflects the actual number of atoms in each molecule. The subscripts are not necessarily the lowest whole-number ratios. 11 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. 12 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. 3

4 A molecular formula does not tell you about a molecule s structure. 13 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. 14 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. The arrangement of atoms within a molecule is called its molecular structure. The arrangement of atoms within a molecule is called its molecular structure. 15 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. 16 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. 4

5 The arrangement of atoms within a molecule is called its molecular structure. Acetylsalicylic acid, also known as aspirin, has a molecular formula of C 9 H 8 O 4. What elements make up acetylsalicylic acid? How many atoms of each element are found in one molecule of acetylsalicylic acid? 17 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. 18 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. Ionic Compounds What representative units define molecular compounds and ionic compounds? The representative unit of a molecular compound is a molecule. For an ionic compound, the smallest representative unit is a formula unit. 19 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. 20 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. 5

6 Recall that a formula unit is the lowest wholenumber ratio of ions in an ionic compound. A molecule is made up of two or more atoms that act as a unit. No such units exist in an ionic compound continuous array of ions There is no such thing as a molecule of sodium chloride or magnesium chloride. Molecular compounds tend to have relatively lower melting and boiling points than ionic compounds. So, Many molecular compounds are gases or liquids at room temperature. 21 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. 22 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. Ionic compounds formed from a metal combined with a nonmetal Higher melting points and boiling points Solids at room temperature Collection of water molecules 1 Molecule of Water made up of 3 atoms Array of sodium ions and chloride ions in a crystal Formula unit of sodium chloride made up of 2 ions Chemical formula H 2 O NaCl Chemical formula 23 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. 24 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. 6

7 How is the formula unit of an ionic compound different from a molecule? 25 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. 7