Although they are composed of ions, ionic compounds are electrically neutral. Most ionic compounds are crystalline solids at room temperature.

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1 Key Concepts Although they are composed of ions, ionic compounds are electrically neutral. Most ionic compounds are crystalline solids at room temperature. Ionic compounds generally have high melting points. Ionic compounds can conduct an electric current when melted or dissolved in water. 46 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

2 CHEMISTRY & YOU What are some properties that are unique to metals? Wrought iron is a very pure form of iron that contains trace amounts of carbon. It is a tough, malleable, ductile, and corrosionresistant material that melts at very high temperatures. 47 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

3 Metallic Bonds and Metallic Properties Metallic bonds are the forces of attraction between the free-floating valence electrons and the positively charged metal ions. These bonds hold metals together. 48 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

4 Metallic Bonds and Metallic Properties Properties of Metals Metals are good conductors of electric current because electrons can flow freely in the metal. Movie-conduction 49 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

5 Metallic Bonds and Metallic Properties Properties of Metals Metals are good conductors of electric current because electrons can flow freely in the metal. As electrons enter one end of a bar of metal, an equal number of electrons leave the other end. 50 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

6 Metallic Bonds and Metallic Properties Properties of Metals Metals are ductile that is, they can be drawn into wires. Force Metal rod Die Wire 51 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

7 Metallic Bonds and Metallic Properties Properties of Metals When a metal is subjected to pressure, the metal cations easily slide past one another. Sea of electrons Force Metal cation Metal 52 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

8 Metallic Bonds and Metallic Properties Properties of Metals When a metal is subjected to pressure, the metal cations easily slide past one another. Sea of electrons Metal cation Metal Force Force Ionic crystal Nonmetal anion Metal cation Strong repulsions If an ionic crystal is struck with a hammer, the blow tends to push the positive ions close together. The positive ions repel one another, and the crystal shatters. 53 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

9 CHEMISTRY & YOU How are metals and ionic compounds different? How are they similar? 54 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

10 CHEMISTRY & YOU How are metals and ionic compounds different? How are they similar? Both metals and ionic compounds form crystal structures. However, they have different configurations of electrons. The sea of electrons surrounding cations in a metal allows metals to be ductile and malleable. Ionic crystals will fracture under pressure. 55 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

11 Alloys Alloys Why are alloys important? Alloys are mixtures of two or more elements, at least one of which is a metal. Brass, for example, is an alloy of copper and zinc. 56 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

12 Alloys Alloys are important because their properties are often superior to those of their component elements. Sterling silver (92.5 percent silver and 7.5 percent copper) is harder and more durable than pure silver, yet it is still soft enough to be made into jewelry and tableware. 57 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

13 Alloys The most important alloys today are steels. The principal elements in most steels, in addition to iron and carbon, are boron, chromium, manganese, molybdenum, nickel, tungsten, and vanadium. Steels have a wide range of useful properties, such as corrosion resistance, ductility, hardness, and toughness. Stainless Steel 80.6% Fe 18.0% Cr 0.4% C 1.0% Ni 58 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

14 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 59 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

15 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. 60 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

16 Molecules and Molecular Compounds In nature, only the noble gas elements, such as helium and neon, exist as uncombined atoms. They are monatomic; that is, they consist of single atoms. Helium, which is less dense than air, is often used to inflate balloons. 61 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

17 Molecules and Molecular Compounds But not all elements are monatomic. O 2 represents two oxygen atoms that are bonded together. Scuba divers breath compressed air, a mixture that contains oxygen gas. 62 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

18 Molecules and Molecular Compounds Ionic compounds are generally crystalline solids with high melting points. Other 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. 63 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

19 Molecules and Molecular Compounds The attractions that hold together the atoms in O 2, H 2 O, CO 2, and N 2 O cannot be explained by ionic bonding. These bonds do not involve the transfer of electrons. 64 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

20 Molecules and Molecular Compounds Sharing Electrons Recall that ionic bonds form when the combining atoms give up or accept electrons. Another way that atoms can combine is by sharing electrons. Atoms that are held together by sharing electrons are joined by a covalent bond. 65 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

21 Molecules and Molecular Compounds 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. 66 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

22 Molecules and Molecular Compounds Sharing Electrons An oxygen molecule is an example of a diatomic molecule a molecule that contains two atoms. Other elements found in nature in the form of diatomic molecules include hydrogen, nitrogen, and the halogens. 67 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

23 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. Water is an example of a molecular compound. 68 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

24 Molecules and Molecular Compounds Representing Molecules A molecular formula is the chemical formula of a molecular compound. 69 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

25 Molecules and Molecular Compounds Representing Molecules A molecular formula shows how many atoms of each element a substance contains. 70 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

26 Molecules and Molecular Compounds Representing Molecules The molecular formula of water is H 2 O. Notice that the subscript written after an element s symbol indicates the number of atoms of each element in the molecule. If there is only one atom, the subscript 1 is omitted. 71 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

27 Molecules and Molecular Compounds Representing Molecules Butane is also a molecular compound. Butane is commonly used in lighters and household torches. The molecular formula for butane is C 4 H 10. According to this formula, one molecule of butane contains four carbon atoms and ten hydrogen atoms. 72 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

28 Molecules and Molecular Compounds Representing Molecules A molecular formula reflects the actual number of atoms in each molecule. The subscripts are not necessarily the lowest whole-number ratios. 73 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

29 Molecules and Molecular Compounds Representing Molecules Note that molecular formulas also describe molecules consisting of atoms of one element. For example, an oxygen molecule consists of two oxygen atoms bonded together; its molecular formula is O Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

30 Molecules and Molecular Compounds Representing Molecules A molecular formula does not tell you about a molecule s structure. In other words, it does not show either the arrangement of the various atoms in space or which atoms are covalently bonded to one another. 75 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

31 Representing Molecules A variety of diagrams and molecular models can be used to show the arrangement of atoms in a molecule. Molecules and Molecular Compounds 76 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

32 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? 77 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

33 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? One molecule of acetylsalicylic acid is made of 9 carbon atoms, 8 hydrogen atoms, and 4 oxygen atoms. 78 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

34 Comparing Molecular and Ionic Compounds Comparing Molecular and Ionic Compounds What representative units define molecular compounds and ionic compounds? 79 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

35 Comparing Molecular 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. 80 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

36 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. 81 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

37 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. In contrast to ionic compounds, which are formed from a metal combined with a nonmetal, most molecular compounds are composed of atoms of two or more nonmetals. 82 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

38 Comparing Molecular and Ionic Compounds Water, which is a molecular compound, and sodium chloride, which is an ionic compound, are compared here. Collection of water molecules Array of sodium ions and chloride ions Molecule of water Formula unit of sodium chloride Chemical formula H 2 O NaCl Chemical formula 83 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

39 ionic-covalent dissolve.swf 84 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

40 BIG IDEA Bonding and Interactions In molecular compounds, bonding occurs when atoms share electrons. In ionic compounds, bonding occurs when electrons are transferred between atoms. 85 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

41 The Octet Rule in Covalent Bonding Single Covalent Bonds The hydrogen atoms in a hydrogen molecule are held together mainly by the attraction of the shared electrons to the positive nuclei. Two atoms held together by sharing one pair of electrons are joined by a single covalent bond. 86 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

42 Single Covalent Bonds Hydrogen gas consists of diatomic molecules whose atoms share only one pair of electrons, forming a single covalent bond. The Octet Rule in Covalent Bonding 87 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

43 The Octet Rule in Covalent Bonding Single Covalent Bonds An electron dot structure such as H:H represents the shared pair of electrons of the covalent bond by two dots. The pair of shared electrons forming the covalent bond is also often represented as a dash, as in H H for hydrogen. A structural formula represents the covalent bonds as dashes and shows the arrangement of covalently bonded atoms. 88 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

44 Coordinate Covalent Bonds The ammonium ion (NH 4+ ) consists of atoms joined by covalent bonds. A polyatomic ion, such as NH 4+, is a tightly bound group of atoms that has a positive or negative charge and behaves as a unit. 89 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

45 Coordinate Covalent Bonds Most polyatomic cations and anions contain covalent bonds. Therefore, compounds containing polyatomic ions include both ionic and covalent bonding. 90 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.