(b) Formation of calcium chloride:

Transcription

1 Chapter 2: Chemical Compounds and Bonding Section 2.1: Ionic Compounds, pages An ionic compound combines a metal and a non-metal joined together by an ionic bond. 2. An electrostatic force holds the positive and negative ions in an ionic bond together. 3. a 4. True 5. (a) Formation of potassium bromide: (b) Formation of calcium chloride: 6. There is no such thing as a single molecule of sodium chloride because sodium chloride is an ionic compound. The smallest subunit of sodium chloride is the formula unit, which consists of many repeating patterns of sodium and chloride. The reason that single molecules of the compound do not exist is that the properties of sodium chloride do not emerge unless many subunits of the pattern exist together in a crystalline structure. For example, the hardness of sodium chloride emerges from the ionic bonds that join each ion to many other ions of the opposite charge, not just a single ion to another ion. 7. Figure 1 Copyright 2011 Nelson Education Ltd. Chapter 2: Chemical Compounds and Bonding 2-1

2 8. Table 1 Properties of Ionic Compounds Property Cause Explanation hardness ionic bonds Ionic bonds are quite rigid and resist being stretched. This gives ionic compounds a hard texture. high melting temperature crystal structure form electrolytes electrostatic forces regular ion arrangement water molecules The electrostatic force between positive and negative ions that holds ionic compounds together is extremely strong and requires a lot of energy to break. Ionic compounds form crystalline structures because positive and negative ions are held tightly and rigidly at regular angles, which creates lattice structure. When placed in water, polar water molecules surround the ions and separate them from one another, causing electrolytes to form. conductivity ion separation When dissolved and broken up into ions, the ions themselves are charged particles. These charged particles are capable of conducting electricity. Section 2.2: Molecular Elements and Compounds, pages False. Unlike ionic compounds, the smallest subunit of a molecular compound is a single molecule. 2. a 3. Molecular compounds are usually made up of atoms that are non-metal, while ionic compounds include both metals and non-metals. 4. Unlike ionic compounds, most molecular compounds usually have low melting points and have low solubility in water. 5. (a) A formula for finding the bonding capacity of an element, given the number of electrons in its valence shell, is as follows: If V is the number of electrons in the valence shell and B stands for bonding capacity, the formula is B = 8 V. For example, using sulfur and chlorine: B S = 8! V = 8 6 and B Cl = 8! V = 8 7 = 2 = 1 6. A lone pair is a pair of electrons that is not involved in covalent bonding. 7. b 8. Covalent bonds result from the sharing of a pair of electrons by two. In an ionic bond, electrons are transferred from one atom to another, forming a positive ion and a negative ion, which are held together by electrostatic force. 9. Lewis structure and structural formula for carbon dioxide, CO 2 : Step 1. Arrange the symbols. Step 2. Count the valence electrons. 1 C atom: 4 e 2 O atoms: 12 e Total: 16 e Step 3. Use Lewis dots to make single covalent bonds. Place lone pairs to satisfy the octet rule for surrounding atoms. Step 4. Place remaining electrons on the central atom. All 16 electrons have been used, so none remain. Step 5. Reposition electrons to give all atoms in the compound a full octet. Copyright 2011 Nelson Education Ltd. Chapter 2: Chemical Compounds and Bonding 2-2

3 Step 6. Replace shared pairs with single or multiple covalent bonds to make a Lewis structure. Remove any lone pairs to make a structural formula. 10. Lewis structure and structural formula for the phosphate ion, PO 4 3. Step 1. Arrange the symbols. Step 2. Count the electrons. 1 P atom: 5 e 4 O atoms: 24 e 3 charge of PO 4 3 : 3 e Total: 32 e Step 3. Use Lewis dots to make single covalent bonds. Step 4. Place lone pairs to satisfy the octet rule for surrounding atoms. Step 5. Compare electrons used to total number of electrons. All 32 electrons have been used, so none remain. The central atom has a full octet. Step 6. Replace the central dots with covalent bonds. Check the finished structure to make sure all atoms have a full octet. Add brackets and a charge. Eliminate lone pairs to form a structural formula. 11. Copyright 2011 Nelson Education Ltd. Chapter 2: Chemical Compounds and Bonding 2-3

4 Section 2.3: Chemical Bonding and Electronegativity, pages False. As the atomic radius of an atom decreases, electronegativity increases. 2. Within a single row of the periodic table, the element farthest to the right side will have the greatest electronegativity. 3. a 4. Table 1 Electronegativity Trends Low electronegativity High electronegativity large atomic radius large ionic radius high first ionization energy location toward left side of periodic table location toward right side of periodic table location toward upper part of periodic table electron affinity metal forms diatomic molecules 5. c 6. No, it is not possible for a diatomic molecule to have a polar-covalent bond. By definition, a diatomic molecule consists of two atoms with the exact same electronegativity value. Therefore, the ΔEN for a diatomic molecule is always zero, so the bond is always non-polar covalent. 7. (a) A compound consisting of two different atoms that have an electronegativity difference of 1.4 is held together by a polar-covalent bond, because its ΔEN is greater than 0 and less than 1.7. (b) This compound would be highly polar. It would be more polar, for example, than the quite polar O H bond that exists in water. 8. Table 2 Covalent, Polar-Covalent, and Ionic Compounds Covalent Polar-covalent Ionic compound compound compound ΔEN 0 > 0 and < example N 2 MgCl NaF atom with greater electronegativity neither Cl F tug-of-war winner neither Cl F 9. The methanol molecule is more likely to be more polar than the methane molecule. The methane molecule has all fairly non-polar C H bonds, so it is likely to be less polar than the methanol molecule, which is asymmetric and includes a fairly polar O H bond, with a ΔEN of 1.4. Section 2.4: Chemical Formulas and Nomenclature, pages An ionic compound that is composed of exactly two different ions is called a binary ionic compound. 2. False. All compounds with a common name also have an IUPAC name. 3. b 4. In the ionic compound 2 (YZ 4 ) 5, if the polyatomic ion YZ 4 has a charge of 2, the ion has a charge of (a) Chemical formula for calcium nitride: Step 1. Write the symbols of the elements with the metal first and the non-metal second. Ca N Step 2. Write the charges above the symbols Ca N Copyright 2011 Nelson Education Ltd. Chapter 2: Chemical Compounds and Bonding 2-4

5 Step 3. Determine how many of each type of ion are required to bring the total charge to zero. 3(+2) + 2( 3) = 0 Ca N Step 4. Write the chemical formula with subscripts. Ca 3 N 2. Step 5. Make sure that the subscripts are a lowest whole number ratio. The chemical formula for calcium nitride is Ca 3 N 2. (b) Chemical formula for magnesium nitrate: Step 1. Write the symbols of the elements with the metal first and the polyatomic ion second. Mg NO 3 Step 2. Write the charges above the symbols Mg NO 3 Step 3. Determine how many of each type of ion are required to bring the total charge to zero. 1(+2) + 2( 1) = 0 Mg NO 3 Step 4. Write the chemical formula with subscripts. Mg 1 (NO 3 ) 2 Step 5. Make sure that the subscripts are a lowest whole number ratio. Omit the subscript 1. The chemical formula for magnesium nitrate is Mg(NO 3 ) 2 6. (a) The IUPAC name for CaFl 2 is calcium fluoride. (b) The IUPAC name for Al 2 O 3 is aluminum oxide. (c) The IUPAC name for Na 2 S is sodium sulfide. (d) The IUPAC name for ZnI 2 is zinc iodide. 7. The IUPAC name for Pb 3 (PO 4 ) 2 : Step 1. This compound contains lead, Pb, which is a multivalent metal that can have a charge of +2 or +4, and phosphate, PO 4, a polyatomic ion that has a charge of 3. 3 Pb 3 (PO 4 ) 2 Step 3. The charge on the Pb ion may be +2 or +4. Step 4. There are 2 phosphate ions, each with a 3 charge. Total negative charge = 6 Step 5. The total positive charge is +6, by the zero-sum rule. This charge is shared between three lead ions, so the charge on each Pb ion is +2. Step 6. The name of Pb 3 (PO 4 ) 2 is lead(ii) phosphate. 8. (a) The IUPAC name of CuCl 2 : Step 1. This compound contains copper, Cu, which is a multivalent metal that can have a charge of +1 or CuCl 2 Step 3. The charge on the Cu ion may be +1 or +2. Step 4. There are 2 chloride ions, each with a 1 charge. Total negative charge = 2 Step 5. The total positive charge is +2,, by the zero-sum rule, so the charge on the copper ion is +2. Step 6. The name of CuCl 2 is copper(ii) chloride. Copyright 2011 Nelson Education Ltd. Chapter 2: Chemical Compounds and Bonding 2-5

6 (b) The IUPAC name of FeBr 2 : Step 1. This compound contains iron, Fe, which is a multivalent metal that can have a charge of +2 or FeBr 2 Step 3. The charge on the Fe ion may be +2 or +3. Step 4. There are 2 bromide ions, each with a 1 charge. Total negative charge = 2 Step 5. The total positive charge is +2,, by the zero-sum rule, so the charge on the iron ion is +2. Step 6. The name of FeBr 2 is iron(ii) bromide. (c) The IUPAC name of FeCl 3 : Step 1. This compound contains iron, Fe, which is a multivalent metal that can have a charge of +2 or FeCl 3 Step 3. The charge on the Fe ion may be +2 or +3. Step 4. There are 3 chloride ions, each with a 1 charge. Total negative charge = 3 Step 5. The total positive charge is +3,, by the zero-sum rule, so the charge on the iron ion is +3. Step 6. The name of FeCl 3 is iron(iii) chloride. (d) The IUPAC name of PbBr 4 : Step 1. This compound contains lead, Pb, which is a multivalent metal that can have a charge of +2 or PbBr 4 Step 3. The charge on the Fe ion may be +2 or +4. Step 4. There are 4 bromide ions, each with a 1 charge. Total negative charge = 4 Step 5. The total positive charge is +4,, by the zero-sum rule, so the charge on the lead ion is +4. Step 6. The name of PbBr 4 is lead(iv) bromide. 9. (a) Name of N 2 O 5 : Does the formula begin with H? No. Are the bonds covalent (ΔEN < 1.7)? Yes. ΔEN for O N = = 0.4 < 1.7, so the bonds are covalent. It is a molecular substance. Are all the elements the same? No. It is a molecular compound. Name each element with the proper prefix: The compound is dinitrogen pentoxide. (b) Name of CuF 2 : Does the formula begin with H? No. Are the bonds covalent (ΔEN < 1.7)? No. ΔEN for F Cu = = 2.1 > 1.7, so the bonds are not covalent. It is an ionic compound. Does the chemical formula begin with a multivalent metal ion? Yes. Name the first element followed by its charge as a Roman numeral: copper(ii). Does the formula contain a polyatomic ion? No. Does the formula contain H 2 O? No. It is a binary ionic compound. Name the ions in the order in which they appear in the chemical formula: The compound is copper(ii) fluoride. (c) Name of Al(NO 3 ) 3 : Does the formula begin with H? No. Are the bonds covalent (ΔEN < 1.7)? No. It is an ionic compound. Does the chemical formula begin with a multivalent metal ion? No. Does the formula contain a polyatomic ion? Yes. Does the formula contain H 2 O? No. It is a polyatomic ionic compound. Name the ions in the order in which they appear in the chemical formula: The compound is aluminum nitrate. Copyright 2011 Nelson Education Ltd. Chapter 2: Chemical Compounds and Bonding 2-6

7 Section 2.5: Explore an Issue in Chemical Compounds: Sugar versus Artificial Sweeteners, page Sugars have no nutritional value other than as a source of energy for the body. 2. False. A sucrose molecule is made of one molecule of glucose joined with one molecule of fructose. 3. a 4. (a) Sucralose is 600 times as sweet as sugar. (b) To get the same level of sweetness in a 1 L pitcher of ice tea as with 100 g of sucrose, you would need to add only 0.17 g of sucralose ( = 0.17). (c) Even though some artificial sweeteners have more calories per gram than sugar, they are called lowcalorie sweeteners because you use such a small amount of them to sweeten a food item that the amount you take in has only a few calories. 5. Table 1 Sweeteners Sweetener Sweetness (1 10) Health benefits Health risk sucrose 3 energy, not carcinogenic obesity, diabetes, other problems fructose 4 energy, not carcinogenic obesity, diabetes, other problems sucralose 10 few calories, less risk of obesity and diabetes aspartame 9 few calories, less risk of obesity and diabetes unsafe only at high doses breakdown products can cause problems Copyright 2011 Nelson Education Ltd. Chapter 2: Chemical Compounds and Bonding 2-7

8 Chapter 2 Summary, page 32 Copyright 2011 Nelson Education Ltd. Chapter 2: Chemical Compounds and Bonding 2-8

9 Chapter 2 Questions, pages False. The smallest unit of an ionic compound is the formula unit. 2. c 3. Table 1 Properties of Ionic Compounds Typical ionic Property compound Reason texture very hard, brittle, breaks easily Ionic bonds resist stretching. The crystal lattice structure is easily offset if the crystal is struck. Ions with the same charge are suddenly side by side and repel one another; the crystal cracks. melting point very high Electrostatic forces (ionic bonds) are very strong and resist breaking. solubility in water electrical conduction 4. Figure 1 very soluble none in solid state; good in liquid state and when dissolved Polar water molecules are able to wedge in between charged ions, causing the compound to break up, or dissolve, releasing free-floating ions into the solution. Ions are charged so they are good carriers of electricity. 5. Formation of lithium oxide: 6. Lewis structure and structural formula for SCl 2 : 7. If in the ionic compound 4 Y 3, the cation has a charge of 3+, the Y anion has a charge of (a) The IUPAC name for K 2 S is potassium sulfide. (b) The IUPAC name for Hg 3 (PO 4 ) 2 is mercury(ii) phosphate. 9. (a) The chemical formula for zinc chromate is ZnCrO 4. (b) The chemical formula for lead(iv) bromide is PbBr The acetic acid molecule is more likely to dissolve in water than the ethane molecule. The ethane molecule has all fairly non-polar C H bonds, so it is likely to be less polar than the acetic acid, which has two polar C O bonds. Since polar molecules are usually more soluble in water than non-polar molecules, you would expect acetic acid to be more soluble. 11. If you add half the normal amount of sweetener to a bottle of pop, and your sweetener is a compound that is half sucrose and half aspartame, the compound is likely to be extremely unsuccessful. Aspartame is 180 times as sweet as sucrose, so the pop will be sickeningly sweet. Copyright 2011 Nelson Education Ltd. Chapter 2: Chemical Compounds and Bonding 2-9