Textbook bonding notes, q and a

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CHAPTER 1

Electrons in Principle Energy

Levels (first 20 elements)

BLM 1.0.2

OVERHEAD

For the first 20 elements, the number of electrons in the outer (valence)

energy level is the same as the last digit of the group number. Note that

with each successive period, there is an additional energy level added to

atoms in that period.

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When metal atoms such as sodium and magnesium lose electrons, they

have no valence electrons remaining. Therefore, there are no dots around

the symbol for the metal ion.

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Calcium fluoride has a ratio of two fluoride ions to one calcium ion. Potassium sulfide

has a ratio of two potassium ions to one sulfide ion.

In the formation of bonds between iron and oxygen and between magnesium and

nitrogen, notice that the metal atoms donate six electrons and the non-metal atoms

accept six electrons. The number of positive and negative charges are balanced.

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In methane, CH4(g), carbon shares each of its valence shell electrons with a

different hydrogen atom. The oxygen atom in water, H2O(ℓ), shares one

electron with each hydrogen atom and also has two lone pairs.

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By sharing two pairs of electrons, the carbon atom and each oxygen atom

in a carbon dioxide molecule can acquire an octet of electrons.

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CHAPTER 1

Rules for Drawing Lewis Structures

BLM 1.1.4

OVERHEAD

Drawing Lewis Structures for Simple Molecules and Polyatomic Ions

Step 1

Determine the total number of valence electrons in all of the atoms

in the molecule. If the molecule has a charge, add or subtract

electrons to account for the charge.

Step 2

Choose the atom with the most unpaired electrons to be the central

atom. Draw a skeleton structure for the molecule by placing the other

atoms around the central atom.

Step 3

Place lone pairs of electrons to form an octet around each of the

atoms except the central atom. Hydrogen, of course, can only have

two electrons in its outer shell.

Step 4 (a)

If all of the valence electrons determined in Step 1 have not been

accounted for, add one or more lone pairs around the central atom

to complete its octet of electrons.

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CHAPTER 1

Thought Lab 1.1: Lewis Structures

BLM 1.1.5

HANDOUT

The rules that you learned for drawing Lewis structures of simple molecules were based on

molecules having a central atom. Many molecules do not have a central atom, but are often written in a way that gives you clues about their structures. In this lab, you will attempt to draw the Lewis structures of some of these molecules. You have already attempted two such molecules, C2H2 and

C2H4. The symmetry of these molecules helped you determine their structure. In many cases,

chemists and biochemists write molecular formulas in groups of atoms. For example, a certain amino acid (glycine) can be written, NH2CH2COOH(s). You can try to isolate the groups, draw their

structures, and then attach them together.

Work with a partner. First, attempt to draw the structures individually. When each of you has found what you believe to be the correct structure, compare your structures. If you do not have the same structure, discuss them and try to come to agreement.

Draw Lewis the structures of the following compounds:

(a) NH2CH2COOH(s)

(b) CH3OCH3(s)

(c) CH3COOH(ℓ)

(d) CF3CHF2(g)

(e) ClCH2CH2SCH2CH2Cl(ℓ)

(f) (NH2)2CO(s)

(g) Challenge! Try to draw the Lewis structure of glucose, C6H12O6(s). Hint: The carbon atoms are

all bonded to each other in a straight chain. Each carbon atom is bonded to at least one hydrogen atom and one oxygen atom.

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(b)

(c)

(d)

(e)

(f)

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Metallic Bonding in Magnesium

OVERHEAD

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In the main group elements, electronegativity increases moving from left to

right across the period, not including noble gases. Within a group,

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In this three-dimensional image of the main group elements, the

electronegativity scale is vertical. The period and group numbers are on the

left and bottom, respectively.

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Character of Bonds

Electronegativity

difference

0.00 0.65 0.94 1.19 1.43 1.67 1.91 2.19 2.54 3.03

Percent ionic character

(%)

0

10

20

30

40

50

60

70

80

90 Percent covalent

character (%)

100

90

80

70

60

50

40

30

20

10

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Multiple-Choice Questions

Circle the letter for the choice that best completes the statement or answers the question.

1. An atom of a metallic element, represented by the symbol X, loses 4 electrons when it combines with a non-metallic element, represented by the symbol, Y. The chemical formula for the

compound that forms is XY2. Which one of the following statements correctly accounts for this

chemical formula?

a) An atom of element Y loses 4 electrons. b) An atom of element Y gains 2 electrons. c) An atom of element Y loses 2 electrons. d) An atom of element Y gains 4 electrons.

2. In the ionic compound PtS, what is the charge on each platinum ion? a) 2+

b) 4

-c) 1

-d) 1+

3. Atoms of elements represented by symbols Q and P combine to form an ionic compound. Each atom of Q loses 2 electrons and each atom of P gains 2 electrons. What is the chemical formula for the compound?

a) Q2P

b) QP2

c) Q2P2

d) QP

4. When atoms of two elements combine, each atom attains a stable electron configuration. Which chemical formula correctly illustrates that this has occurred?

a) LiO2

b) Na2I

c) MgS d) Zn2O

5. Atoms of nitrogen and hydrogen bond to form the compound NH3. When this bonding occurs,

which one of the following statements is correct?

a) One atom of nitrogen transfers three electrons to three hydrogen atoms. b) One hydrogen atom shares three electrons with each nitrogen atom. c) Each hydrogen atom shares three electron pairs with a nitrogen atom. d) Each hydrogen atom shares one pair of electrons with nitrogen.

6. What is the correct IUPAC name for the compound Sn(SO4)2?

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7. A researcher reports that ions of Br2- have been detected. Which answer is most consistent with the formation of these ions?

a) Each ion must have more than eight electrons in the outer energy level. b) Each bromine atom gained two electrons.

c) Br2-_{is not expected to be a stable ion of bromine.}

d) All of the above statements are correct.

8. The chemical compounds potassium sulfide, K2S, and sulfur dioxide, SO2, illustrate that atoms of

sulfur

a) always share electrons

b) always form polar covalent bonds

c) can become stable by either the transfer or sharing of electrons d) can act as both a metal and a non-metal

9. What element does the diagram on the right represent? a) a nickel atom

b) a silicon atom c) a germanium atom d) an oxygen ion

10. Which answer below shows, in the correct order, the formulas of the compounds magnesium nitrite, magnesium nitride, and magnesium nitrate?

a) Mg3N2,Mg(NO2)2, Mg(NO3)2

b) Mg(NO2)2, Mg3N2, Mg(NO3)2

c) Mg(NO3)2, Mg(NO2)2, Mg3N2

d) Mg3N2, Mg(NO3)2, Mg(NO2)2

11. An element has an electronegativity of 2.6. What statement concerning this element is not

correct?

a) It is a metal and will transfer electrons to a non-metal. b) It will form polar covalent bonds with bromine. c) It will form ionic bonds with potassium.

d) It will form n covalent bonds with carbon.

12. Which one of the following is a correct electron dot diagram for calcium sulfide?

13. The symbols G, H, I, and J represent four consecutive elements in the periodic table. Element I is a Group 18 element. What is the expected formula of a compound formed between elements G and J?

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14. A newly discovered element, represented by the symbol Z, forms a stable compound with nitrogen having the chemical formula ZN. Using the chemical formula X to represent any halogen, what is the expected chemical formula of the compound that forms between element Z and a halogen?

a) ZX b) ZX2

c) ZX3

d) ZX4

15. If the element titanium (electronegativity = 1.5) is alloyed with the element iridium (electronegativity = 2.2), the bonding in this alloy is best described as

a) metallic b) ionic c) covalent d) polar covalent

16. Two elements combine to form a binary compound. What information about two atoms is the most reliable predictor of the chemical formula of the compound?

a) total number of electrons in each atom b) number of valence electrons in each atom c) electronegativity of each atom

d) knowing if the elements are metals or non-metals

17. Intramolecular bonding between atoms is usually described as one of the following types:

ionic non-polar covalent polar covalent metallic

What will be the correct ordering of the numbered definitions when arranged to match the order of the listed bond types?

1

unequal sharing of electrons between

two atoms

2

the attraction between free electrons and positively charged ions

3

simultaneous attraction of oppositely charged

ions

4

electrons are equally shared between two

atoms

a) 3, 4, 1, 2 b) 3, 1, 4, 2 c) 1, 4, 1, 3 d) 2, 4, 3, 1

18. Phosphorus atoms (atomic number 15) can form the phosphide ion, P3-_{. What is the correct}

electron population in the first four energy levels of this ion? a) 2, 8, 5, 0

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19. Four of the chemicals in the table below are classified as ionic compounds. Which numbers correspond to the ionic compounds?

1. NaCl(s) 4. HgCO3(s) 7. K2SO4(aq)

2. H2O(l) 5. HF(aq) 8. C3H8(g)

3. PF5(g) 6. Sb3N5(s) 9. CaF2(s)

a) 1, 4, 5, 9 b) 1, 4, 6, 7 c) 1, 6, 7, 9 d) 1, 4, 7, 9

20. What is the electric charge on the ion “X” in the ionic compound XIO2?

a) 1+

b) 2+

c) 3+

d) 4+

Written Response Questions

Answer each question in the space provided. Use complete sentences and diagrams where necessary.

21. A student answer on a test about chemical bonding contained the following sentence: "When elements combine, they gain or lose electrons to become a noble gas."

a) What is incorrect in this statement?

________________________________________________________________________

b) Rewrite this statement to correct the error that has been made.

________________________________________________________________________

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22. C2H4Cl2(g) is a molecular compound called 1,2-dichloroethane that is produced in the

petrochemical industry.

a) Draw a Lewis structure to represent a molecule of 1,2-dichloroethane.

b) Classify the C—Cl, C—C, and C—H bonds in this molecule as non-polar covalent or polar covalent. Explain the reason for your classification.

______________________________________________________________________________

c) The C—Cl bond is polar covalent. Which atom would be labelled as δ+? Give a reason for your answer.

______________________________________________________________________________

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23. Draw structural formulas for each of the following four compounds: a) N2F4

b) C2H2Cl2

c) S2

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24. The element tin can bond with carbon, phosphorus, and iodine. Refer to the electronegativities shown in the periodic table and arrange the bonds formed between tin and each of these elements, from least polar to most polar.

______________________________________________________________________________

25. Some elements form ions with more than one charge. For example, copper forms Cu+_{and Cu}2+

ions. These ions differ in the size of their ionic radius. Which ion would be expected to be larger? Give an explanation for your answer.

______________________________________________________________________________

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27. For each pair of molecules shown below, either the Lewis structure or the corresponding structural formula is incorrect. Identify the error in each pair and draw a correct form of the molecule.

Lewis structure Structural formula Correction

Answers to Multiple-Choice Questions

1. b 2. a 3. d 4. c 5. d 6. c 7. d 8. c 9. b 10. b 11. a 12. d 13. b 14. c 15. a 16. b 17. a 18. a 19. d 20. a

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21. a) An ionic bond forms when the atoms of the metallic element lose electrons and the atoms of the non-metallic element gain electrons. Each ion attains the same electron configuration as a noble gas. There is no change in the nucleus. The ion does not turn into a noble gas.

b) When elements combine they gain or lose electrons so that each ion has the same electron configuration as a noble gas.

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b) Determine the difference in electronegativity (EN) for each bond.

Bonds are classified based on EN. For EN = 0, the bond is pure covalent.

For EN between 0 and 0.5, the bond is slightly polar covalent. For EN between 0.5 and 1.7, the bond is polar covalent. C—Cl EN = 3.2 - 2.6 = 0.6. This is a polar covalent bond. C—C EN = 2.6 - 2.6 = 0.0. This is a non-polar covalent bond. C—H EN = 2.6 - 2.2 = 0.4. This is a slightly polar covalent bond.

c) +

-C—Cl

C is less electronegative than Cl and will therefore attract the shared pair of electrons less strongly.

23. a) Structural formula for N2F4

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c) Structural formula for S2

d)Structural formula for CHBr2F

24. Sn-C EN = 2.6 - 2.0 = 0.6 Sn-P EN = 2.2 - 2.0 = 0.4 Sn-I EN = 2.7 - 2.0 = 0.7

Therefore, in order increasing difference in electronegativity: Sn - P Sn – C  Sn - I

25. Copper has an atomic number of 29. There are 29 protons in the nucleus regardless of whether this is copper atom or copper ion. For Cu1+_{, there are 28 electrons attracted to the 29 protons in}

the nucleus; for Cu2+_{, there are 27 electrons attracted to the 29 protons in the nucleus. Cu}1+_is

larger because there is less attraction per electron in this ion.

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27. a) The Lewis structure is not correct.

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CHAPTER 2

Sodium Chloride Crystal

BLM 2.1.2

OVERHEAD

Sodium and chloride ions

packed together in crystals

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CHAPTER 2

VSEPR Shapes: Linear

BLM 2.1.5

OVERHEAD

Carbon dioxide and hydrogen cyanide are linear molecules of class AX2.

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VSEPR Shapes: Trigonal Planar

OVERHEAD

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CHAPTER 2

VSEPR Shapes: Bent

BLM 2.1.7

OVERHEAD

Bent molecules have two lone pairs. There is repulsion between the two

lone pairs due to their bulkiness. The bond angle is 104.5°.

CHAPTER 2

VSEPR Shapes: Tetrahedral

BLM 2.1.8

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Tetrahedral shapes are three dimensional. You need to analyze the

perspective until you can see that, in this image, lines going upward are in

the plane of the page. The lower line on the right is coming out from the

page and the upper line on the right is going into the page.

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Molecular Shapes

OVERHEAD

VSEPR Class

Name of

molecular

shape

Type of

electron pairs

Shape

Example

AX2 linear all BP CO2

AX3 trigonal planar all BP CH2O

AX2E

bent (trigonal planar electron

groups)

2 BP, 1 LP SO2

AX4 tetrahedral all BP CH4

AX3E

trigonal pyramidal (tetrahedral electron groups)

3 BP, 1 LP NH3

AX2E2

bent (tetrahedral

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CHAPTER 2

Dipoles and Polarity

BLM 2.1.11

OVERHEAD

The presence of polar bonds does not ensure that the molecule is polar.

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Molecular Shapes and Polarity

OVERHEAD

Molecular shape Bond polarity Molecular polarity

linear non-polar

linear polar

bent polar

trigonal planar non-polar

trigonal planar polar

tetrahedral non-polar

tetrahedral polar

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Intermolecular Forces: Dipole–

Dipole Attractions

OVERHEAD

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CHAPTER 2

Intermolecular Forces:

Hydrogen Bonding

BLM 2.2.3

OVERHEAD

Individual hydrogen bonds are much weaker than covalent bonds.

However, when many hydrogen bonds are acting on each water molecule at

the same time, they have a significant effect on the properties of water.

The hydrogen bonds in ice are longer than they are in water, making ice

less dense than liquid water. It is the orientation of the hydrogen bonds in

ice that gives them their maximum strength.

A

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CHAPTER 2

Induced Dipoles

BLM 2.2.5

OVERHEAD

The force that holds the balloon to the wall is an electrostatic force between

the positively charged spot on the balloon and the negative end of the

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CHAPTER 2

Comparing Dispersion Forces in

Isotopes

BLM 2.2.6

OVERHEAD

Both types of molecules have five carbon atoms and 12 hydrogen atoms but

their shapes are quite different. London (dispersion) forces are greater

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Bonding in Solid, Liquid, and Gas

Phases

OVERHEAD

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CHAPTER 2

Melting and Boiling Points of Some

Common Compounds

BLM 2.3.2

OVERHEAD

Metals

Substance Melting point (°C) Boiling point (°C)

Li(s) 181 1342

Sn(s) 232 2602

Al(s) 660 2519

Ag(s) 962 2162

Cu(s) 1085 2562

Ionic Compounds

CsBr(s) 636 1300

NaI(s) 661 1304

MgCl2(s) 714 1412

NaCl(s) 801 1413

MgO(s) 2825 3600

Molecular substances

H2(g) –259 –253

Cl2(g) –101 –34

H2O(ℓ) 0 100

C6H6O(ℓ) 6 80

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Boiling Points of Binary

Hydrides

OVERHEAD

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Multiple-Choice Questions

Circle the letter for the choice that best completes the statement or answers the question.

1. The bonds in a network solid responsible for the hardness and rigidity are a) hydrogen bonds

b) dipole-dipole forces c) ionic bonds

d) covalent bonds

2. In an ionic lattice, the structure is made up of a repeating pattern of

a) atoms all linked by covalent bonds

b) formula units in a geometric arrangement of unit cells c) positive ions in a sea of electrons

d) positive ends of one molecule attracted to the negative end of another

Use the structures below to answer questions 3 and 4. (i) (ii) (iii) (iv)

3. Each of the Lewis structures above has the molecular formula C2H6O. Which Lewis structures

are correct?

a) (i) and (iii) only

b) (i), (ii), and (iii) only

c) (i) and (ii) only

d) All are possible correct structural formulas.

4. Which one of the following statements is correct about Lewis structure (i)? a) The molecule is bent and is a dipole.

b) The molecule is linear and is a dipole.

c) Hydrogen bonding can occur between molecules. d) There is a double bond to the oxygen atom.

5. In ice, what type of bonds are the strongest?

a) hydrogen bonding between molecules of H2O

b) London (dispersion) forces between molecules of H2O

c) covalent bonds between hydrogen and oxygen atoms in molecules of H2O

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6. Which one of the following compounds would be expected to have the highest boiling point? a) SiO2 c) LiCl

b) C6H13OH d) KCl

7. In a network solid, the lattice points consist of

a) atoms

b) polar molecules c) ions

d) non-polar molecules

8. The bromate ion, BrO3-(aq), has a pyramidal molecular shape. Which structure shown below is

consistent with the pyramidal shape of this molecule?

9. According to VSEPR theory, electron groupings in the valence shell of the central atom of a molecule arrange themselves in order that

a) the electronegativity difference between atoms is a minimum b) the molecule has the most symmetrical shape

c) the electron groupings are as far apart as possible d) the repulsion between them is maximized

10. Which statement about the properties of molecules of CH2O is correct?

a) It is trigonal pyramidal in shape and is a dipole. b) It is trigonal planar in shape and is a dipole. c) It is tetrahedral in shape and non-polar. d) It is linear in shape and non-polar.

11.Which of the following molecules would be pyramidal in shape?

a) SO2(g) c) CF4(g)

b) CS2(l) d) NI3(s)

12. Which one of the following compounds will have the highest boiling point? a) CH3OCH3(l)

b) C3H8(l)

c) C3H5OH(l)

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13. Which one of the compounds listed below has only London (dispersion) forces between molecules?

a) C4H9OH(l)

b) K2Cr2O7(s)

c) C6H6(l)

d) CH2F2(g)

14.Which of the following molecules would be polar?

a) CO2(g)

b) CH3OCH3(g)

c) CF4(g)

d) NI3(s)

15. Which one of the following compounds is least likely to dissolve in a polar liquid? a) CCl4(l)

b) CH3OH(l)

c) H2S(g)

d) NH3(g)

16. Argon is a noble gas that freezes to a solid at -189 °C. What type of bonds will form between atoms of argon in the solid state?

a) metallic b) covalent

c) London dispersion forces d) dipole-dipole

17. Water (H2O) boils at 100 °C and hydrogen sulfide (H2S) boils at -61 °C. Which statement

explains this difference in boiling point?

a) The total number of electrons is greater in H2S than in H2O.

b) There are stronger dipole-dipole attractions between H2O molecules.

c) There are greater London dispersion forces between H2O molecules.

d) The molar mass of H2S is greater than the molar mass of H2O.

18. The molecular shape of a molecule may be described as one of the

following:

bent trigonal planar tetrahedral pyramidal

What will be the correct ordering of the numbered examples when arranged to match the order of the listed molecular shapes?

1 CH2O(l)

2 PH3(g)

3 SiCl4(l)

4 OF2(g)

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19. Four of the chemicals in the table below can be classified as polar covalent solids at certain temperature and pressure conditions. Which numbers correspond to these polar covalent solids?

1. NaCl(s) 4. CCl4(l) 7. K2SO4(s)

2. CH3Br(g) 5. HF(g) 8. C13H28(l)

3. PI3(s) 6. CO2(g) 9. OF2(g)

a) 3, 6, 8, 9 b) 2, 3, 5, 9 c) 2, 4, 5, 9 d) 2, 3, 4, 9

20. The following are formulas for covalent compounds. Each is attracted to

molecules like itself by different strengths of intermolecular forces. Reorder

the formulas below so they correspond to the expected order of their boiling temperatures, from lowest to highest.

1 H2O(l)

2 CH4(g)

3 C4H10(g)

4 CH2Cl2(l)

a) 2, 3, 4, 1

b) 2, 4, 3, 1

c) 1, 3, 4, 2

d) 4, 3, 2, 1

Written Response Questions

Answer each question in the space provided. Use complete sentences and diagrams when necessary.

21. The angle between C—H bonds in CH4 is 109.5°. Will this angle between C—H bonds increase,

remain the same, or decrease in the molecule CH3Cl? Give a reason for your answer.

_________________________________________________________________________________

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22. The structural formulas for two compounds that can be derived from ethene are shown below. One has a boiling point of 108 °C and the other boils at 47 °C. Which compound has the lower boiling point? Give a reason for your answer.

1,2,-dibromoethene 1,2,-dichloroethene

________________________________________________________________________________

_________________________________________________________________________________

23. The structural formulas for three alcohols are shown below.

propan-1-ol propane-1,2-diol propane-1,2,3-triol

Compare the intermolecular bonding that is present in these three molecules.

_________________________________________________________________________________

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24. Why is a chemical formula for a compound such as ethylene dichloride, C2H4Cl2, not reduced to

a simplest whole-number ratio as would be the case for an ionic compound?

_________________________________________________________________________________

25. One end of a piece of copper wire, which is 30 cm in length, is heated until it is red hot. In a short period of time, the opposite end of the wire becomes warm but not red hot. Explain what has happened in terms of the structure of copper.

_________________________________________________________________________________

26. Tests are carried out on a solid to determine the nature of the bonding in the sample. It does not dissolve to any appreciable degree in water, it does not conduct electric current, and it has a melting point above 650 °C.

a) Based on these results, what type of bonding can be ruled out for this sample? Explain your reasoning for this answer.

_________________________________________________________________________________

b) What additional experimental test can be carried out to determine the type of bonding in the sample. Explain what the result of this experimental test would tell you about the nature of the bonding in the sample.

_________________________________________________________________________________

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Answers to Multiple-Choice Questions 1. d 2. b 3. c 4. a 5. c 6. a 7. a 8. b 9. c 10. b 11. d 12. c 13. c 14. d 15. a 16. c 17. b 18. d 19. b 20. a

Answers to Written Response Questions

21. The angle between C—H bonds will decrease. In CH4, there is equal repulsion between the bond

pairs and the C—H bonds spread as far apart as possible to the maximum bond angle of 109.5 o_{C. In CH}

3Cl, the repulsion between the larger Cl atom and the C—H bond pairs is greater

than the repulsions between bond pairs in CH4. The C—H bond pairs will move closer together,

decreasing the angle between the C—H bonds.

22. When a liquid boils, the heat energy is used to overcome the intermolecular forces of attraction between molecules and the molecules move farther apart. London dispersion forces between molecules increase with an increase in the number of electrons in the molecule. Since chlorine atoms have fewer electrons than bromine atoms, the1,2-dichloroethene has weaker London dispersion forces. Therefore, less energy is needed to spread the molecules apart and 1,2-dichloroethene will boil at the lower temperature of 47 o_C.

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larger London dispersion forces between molecules. The intermolecular bonding will increase in the order:

propan-1-ol  propane-1,2-diol  propane-1,2,3-ol

24. In an ionic compound, ions are not bonded in pairs as independent units. Each ion is attracted to all of the surrounding neighbouring ions. Therefore, the chemical formula represents the simplest whole-number ratio of ions. In a molecular compound such as C2H4Cl2, all of the atoms are

bonded together to form one discrete molecule. The chemical formula must represent all of the atoms present in the molecule.

25. The model of the metallic bond would describe positive copper ions immersed in a sea of free electrons. As one end of the wire is heated, the kinetic energy of the free electrons increases. This energy is passed from electron to electron along the wire. More rapid movement of particles is detected as a rise in temperature. As the electrons in the opposite end of the wire increase in kinetic energy, they move faster and the wire heats up. The wire will not get red-hot at the opposite end because some of the kinetic energy is lost to the air around the wire.

26. a) Metallic bonding can be ruled out because the solid did not conduct electric current. The intermolecular bonding between molecules in a molecular solid are formed by much weaker attractive forces than those found in ionic or metallic bonding and can thus be ruled out because the melting point is very high. Although many ionic compounds are soluble in water, some are not; therefore, ionic bonding cannot be ruled out.