Chapter 7 Ionic and Metallic Bonding

Transcription

1 Chapter 7 Ionic and Metallic Bonding 7.1 Ions 7.2 Ionic Bonds and Ionic 7.3 Bonding in Metals 1 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

2 CHEMISTRY & YOU Where does table salt come from? In some countries, salt is obtained by the evaporation of seawater. In other countries, salt is mined from rock deposits deep underground. 2 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

3 Formation of Ionic Formation of Ionic What is the electrical charge of an ionic compound? 3 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

4 Formation of Ionic Sodium chloride, or table salt, is an ionic compound consisting of sodium cations and chloride anions. An ionic compound is a compound composed of cations and anions. 4 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

5 Formation of Ionic Although they are composed of ions, ionic compounds are electrically neutral. The total positive charge of the cations equals the total negative charge of the anions. 5 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

6 Formation of Ionic Ionic Bonds Anions and cations have opposite charges and attract one another by means of electrostatic forces. The electrostatic forces that hold ions together in ionic compounds are called ionic bonds. 6 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

7 When 7.2 Ionic sodium Bonds and Ionic chlorine react > to form a compound, the sodium atom transfers its one valence electron to the chlorine atom. Sodium and chlorine atoms combine in a one-to-one ratio, and both ions have stable octets. Formation of Ionic 7 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

8 Aluminum metal (Al) and the nonmetal bromine (Br 2 ) react violently to form the ionic solid aluminum bromide (AlBr 3 ). Each bromine atom has seven valence electrons and readily gains one additional electron. Formation of Ionic Three bromine atoms combine with each aluminum atom. 8 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

9 Formation of Ionic Formula Units A chemical formula shows the numbers of atoms of each element in the smallest representative unit of a substance. NaCl is the chemical formula for sodium chloride. 9 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

10 Formation of Ionic Ionic compounds do not exist as discrete units, but as collections of positively and negatively charged ions arranged in repeating patterns. 10 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

11 Formation of Ionic The chemical formula of an ionic compound refers to a ratio known as a formula unit. A formula unit is the lowest wholenumber ratio of ions in an ionic compound. 11 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

12 For sodium chloride, the lowest wholenumber ratio of the ions is 1:1 (one Na + ion to each Cl ion). Formation of Ionic The formula unit for sodium chloride is NaCl. Although ionic charges are used to derive the correct formula, they are not shown when you write the formula unit of the compound. 12 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

13 Predicting Formulas of Ionic Use electron dot structures to predict the formulas of the ionic compounds formed from the following elements: Yes Positive Is this correct??!!! ion first!!! a. potassium and oxygen b. magnesium and nitrogen 13 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

14 1 Analyze Identify the relevant concepts. Atoms of metals lose valence electrons when forming an ionic compound. Atoms of nonmetals gain electrons. Enough atoms of each element must be used in the formula so that electrons lost equal electrons gained. 14 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

15 2 Solve Apply the concepts to this problem. a. Start with the atoms. K and O 15 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

16 a. In order to have a completely filled valence shell, the oxygen atom must gain two electrons. These electrons come from two potassium atoms, each of which loses one electron. K K + O K + O K Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

17 a. Express the electron dot structure as a formula. The formula of the compound formed is K 2 O (potassium oxide). 17 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

18 2 Solve Apply the concepts to this problem. b. Start with the atoms. Mg and N 18 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

19 b. Each nitrogen atom needs three electrons to have an octet, but each magnesium atom can lose only two electrons. Three magnesium atoms are needed for every two nitrogen atoms. Mg Mg Mg N + Mg 2+ N Mg 2+ Mg 2+ N N Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

20 b. Express the electron dot structure as a formula. The formula of the compound formed is Mg 3 N 2 (magnesium nitride). 20 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

21 Use electron dot structures to determine the formula of the ionic compound formed when calcium reacts with fluorine. 21 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

22 Use electron dot structures to determine the formula of the ionic compound formed when calcium reacts with fluorine. Ca F + Ca 2+ F F F CaF 2 22 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

23 Properties of Ionic Properties of Ionic What are three properties of ionic compounds? 23 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

24 Properties of Ionic Most ionic compounds are crystalline solids at room temperature. The component ions in such crystals are arranged in repeating three-dimensional patterns. The beauty of crystalline solids comes from the orderly arrangement of their component ions. 24 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

25 Properties of Ionic Each ion is attracted strongly to each of its neighbors, and repulsions are minimized. The large attractive forces result in a very stable structure. 25 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

26 Properties of Ionic Ionic compounds generally have high melting points. 26 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

27 CHEMISTRY & YOU Would you expect to find sodium chloride in underground rock deposits as a solid, liquid, or gas? Explain. 27 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

28 CHEMISTRY & YOU Would you expect to find sodium chloride in underground rock deposits as a solid, liquid, or gas? Explain. Sodium chloride is found in underground rock deposits as a solid. Like most ionic compounds, sodium chloride has a high melting point (about 800 C). 28 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

29 Properties of Ionic The coordination number of an ion is the number of ions of opposite charge that surround the ion in a crystal. In NaCl, each ion has a coordination number of 6. The coordination number of Na + is 6 because each Na + ion is surrounded by six Cl ions. 29 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

30 Properties of Ionic The coordination number of Cl is also 6 because each Cl ion is surrounded by six Na + ions. 30 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

31 Properties of Ionic In CsCl, each ion has a coordination number of 8. Each Cs + ion is surrounded by eight Cl ions. Each Cl ion is surrounded by eight Cs + ions. 31 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

32 Titanium dioxide (TiO 2 ), or rutile, forms tetragonal crystals. The coordination number for the cation (Ti 4+ ) is 6. Properties of Ionic Each Ti 4+ ion is surrounded by six O 2 ions. 32 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

33 Properties of Ionic The coordination number of the anion (O 2 ) is 3. Each O 2 ion is surrounded by three Ti 4+ ions. 33 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

34 Properties of Ionic Ionic compounds can conduct an electric current when melted or dissolved in water. 34 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

35 When sodium chloride is melted, the orderly crystal structure breaks down. If a voltage is applied across this molten mass, cations migrate freely to one electrode and anions migrate to Flow of electrons Power source Inert metal electrodes Properties of Ionic Current meter the other. To (+) electrode Flow of electrons Cl Na + To ( ) electrode 35 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

36 Properties of Ionic This movement of electrons allows electric current to flow between the electrodes through an external wire. To (+) electrode Flow of electrons Power source Inert metal electrodes Current meter Flow of electrons Cl Na + To ( ) electrode 36 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

37 Properties of Ionic This solar facility uses molten NaCl for its ability to absorb and hold a large quantity of heat, which is used to generate electricity. 37 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

38 Properties of Ionic Ionic compounds also conduct electric current if they are dissolved in water. When dissolved, the ions are free to move about in the solution. 38 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

39 When can ionic compounds conduct an electric current? A. Only when melted B. When melted or dissolved in water C. Only when dissolved in water D. When solid or melted 39 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

40 When can ionic compounds conduct an electric current? A. Only when melted B. When melted or dissolved in water C. Only when dissolved in water D. When solid or melted 40 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

41 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. 41 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

42 Glossary Terms ionic compound: a compound composed of positive and negative ions ionic bond: the electrostatic attraction that binds oppositely charged ions together chemical formula: an expression that indicates the number and type of atoms present in the smallest representative unit of a substance 42 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

43 Glossary Terms formula unit: the lowest whole-number ratio of ions in an ionic compound; in magnesium chloride, the ratio of magnesium ions to chloride ions is 1:2 and the formula unit is MgCl 2 coordination number: the number of ions of opposite charge that surround each ion in a crystal 43 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

44 BIG IDEA Bonding and Interactions The electrostatic forces between the oppositely charged ions hold the cations and anions together in an ionic compound. Ionic compounds generally have high melting points and can conduct an electric current in solution and in the molten state. 44 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

45 END OF Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.