Chapter 8 Covalent Bonding 8.1 Molecular Compounds 8.2 The Nature of Covalent Bonding 8.3 Bonding Theories 8.4 Polar Bonds and Molecules Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

CHEMISTRY & YOU How are atoms joined together to make compounds with different structures? Although the types of pieces are limited, you can make many different toy models depending on how many pieces you use and how they are arranged. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds What information does a molecular formula provide? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds In nature, only the noble gas elements, such as helium and neon, exist as uncombined atoms. They are monatomic; so they consist of single atoms. But not all elements are monatomic. Oxygen exists in molecules as O2. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Ionic compounds are generally crystalline solids with high melting points. Other compounds, however, have very different properties. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Ionic compounds are generally crystalline solids with high melting points. Other compounds, however, have very different properties. Water (H2O) is a liquid at room temperature. Carbon dioxide (CO2) and nitrous oxide (N2O) are both gases at room temperature. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds The attractions that hold together the atoms in O2, H2O, CO2, and N2O cannot be explained by ionic bonding. These bonds do not involve the transfer of electrons. Another way that atoms can combine is by sharing electrons. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Sharing Electrons Remember that ionic bonds form when the combining atoms give up or accept electrons. Atoms that are held together by sharing electrons are joined by a covalent bond. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Sharing Electrons A molecule is a neutral group of atoms joined together by covalent bonds. An oxygen molecule is an example of a diatomic molecule—a molecule that contains two atoms, like oxygen, O2. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Sharing Electrons Molecules can also be made of atoms of different elements. A compound composed of molecules is called a molecular compound. H2O is an example of a molecular compound. A molecular formula is the chemical formula of a molecular compound. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds A molecular formula shows how many atoms of each element a substance contains. The molecular formula of carbon dioxide is CO2. The subscript written after an element’s symbol shows the number of atoms of each element in the molecule. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Representing Molecules Butane is another a molecular compound. Butane is used in lighters and household torches. The molecular formula for butane is C4H10. According to this formula, one molecule of butane contains four C atoms and ten H atoms. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Representing Molecules A molecular formula does not tell you how the atoms are arranged in space or which atoms are bonded to one another structure. The arrangement of atoms within a molecule is called its molecular structure. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Representing Molecules The molecular structure of CO2 shows how the 3 atoms are arranged in a row. It also shows how the C atom is in the middle between the two oxygen atoms. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Representing Molecules The molecular structure of ethanol (C2H6O) is more complicated. Each C is bonded to four atoms, each H is bonded to one atom, and the one oxygen is bonded to two atoms. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Comparing Molecular and 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. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Comparing Molecular and Ionic Compounds Molecular compounds tend to have relatively lower melting and boiling points than ionic compounds. Many molecular compounds are gases or liquids at room temperature. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Comparing Molecular and Ionic Compounds Molecular compounds tend to have relatively lower melting and boiling points than ionic compounds. Many molecular compounds are gases or liquids at room temperature. Most molecular compounds are composed of atoms of two or more nonmetals. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Comparing Molecular and Ionic Compounds Water, which is a molecular compound, and sodium chloride, which is an ionic compound, are compared here. Array of sodium ions and chloride ions Collection of water molecules Formula unit of sodium chloride Molecule of water Chemical formula H2O NaCl Chemical formula Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

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

How is the formula unit of an ionic compound different from a molecule? A molecule is made up of two or more atoms that act as a unit. No such discrete units exist in an ionic compound, which exists as an array of ions. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Key Concepts A molecular formula shows how many atoms of each element a substance contains. The representative unit of a molecular compound is a molecule. For an ionic compound, the smallest representative unit is a formula unit. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

covalent bond: a bond formed by the sharing of electrons between atoms Glossary Terms covalent bond: a bond formed by the sharing of electrons between atoms molecule: a neutral group of atoms joined by covalent bonds diatomic molecule: a molecule consisting of two atoms Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

molecular compound: a compound that is composed of molecules Glossary Terms molecular compound: a compound that is composed of molecules molecular formula: a chemical formula of a molecular compound that shows the kinds and numbers of atoms present in a molecule of a compound Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

List three examples of covalent bonding. 3. What is a molecule? Questions What is a covalent bond? List three examples of covalent bonding. 3. What is a molecule? 4. What is a molecular formula? 5. What is the representative unit in a molecular compound? 6. List two ways that molecular compounds are different from ionic compounds. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.