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Chapter 3 - Molecules, Compounds, and

Chemical Equations

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In this chapter we will build on your understanding of compounds.

• forces of attraction within compounds- chemical bonds

• representing and naming compounds - types of chemical formulas- chemical nomenclature

• quantitative aspects of compounds- percent composition- using experimental data to determine chemical formulas

• representing how compounds change and react- chemical equations

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2 H2 (g) + O2 (g) → 2 H2O (l)

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I. Chemical Bonds

• The overwhelming majority of elements occur in chemical combination with other elements.

• Why are most atoms found bonded to other atoms in the form of chemical compounds?

• What causes compound formation?

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A.Ionic Bonds

1. Ionic bonds are usually between a metal and a non-metal.

2. How does an ionic bond form?Video – Reaction of Na (s) + Cl2 (g)http://www.youtube.com/watch?v=Ftw7a5ccubs

3. Ionic compounds are not composed of molecules.

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B. Covalent Bonds

1. Usually between two non-metal atoms.

2. How does a covalent bond form?

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In which of the following arrangements is the negative charge most stabilized?

A. B. C.

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3. The fundamental repeating unit of covalently bonded substances is the molecule.

a. Representing molecules

1. ball and stick model

2. space - filling model

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Ball and Stick Model of Caffeine

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Space Filling Model of Caffeine

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3. Molecular Formula

4. Structural Formula

5. Empirical Formulas

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D. Some substances contain ionic and covalent bonds.

For example, CaCO3

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C. Attractive forces between molecules are not chemical bonds.

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6) What is the empirical formula for C4H10O2?

A) C2H5O

B) CHO

C) C2H4O

D) CHO2

E) CH2O

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Which of the following contains BOTH ionic and covalent bonds?

A) CaI2

B) COS

C) NH4Cl

D) SF6

E) None of the above contain both ionic and covalent bonds.

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II. Nomenclature and Formula Writing – Ionic Compounds

A. Formula Writing – Ionic Compounds

1. Positive ion is written first2. Sum of charges should equal zero.3. Formulas for ionic compounds contain the

lowest ratio of ions.4. Use parentheses when indicating more than

one polyatomic ion.

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5. Formula Writing – Examples

K+ S2-

NH4+ SO4 2-

Fe 3+ SO3 2-

Pb 4+ O 2-

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B. Nomenclature – Ionic Compounds

1. Cation read first.

2. Anion read second. • monoatomic anions - end in “ide” • polyatomic “oxyanions” –

end in “ate” and “ite”3. Practice

FeP Cu2Cr2O7 Hg2Cl2

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C. Hydrates1. A hydrate is an ionic compound with

a specific number of water moleculesassociated with each formula unit.

2. Water can be driven off by heating.

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III. Nomenclature and FormulaWriting – Molecular Compounds

A. Binary molecular compounds

CO vs CO2

1. All end in “ide”.2. Use Latin numerical prefixes to indicate

the numbers of each type of atom.3. Drop “mono” from first element if mono

is used.

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B. Organic Compounds

1. Organic compounds are carbon-based.(C,H, and O,N,S, X)

2. Organic compounds include biomolecules, pharmaceuticals, plastics,textiles, DNA, etc.

3. Simple hydrocarbons – Alkanes

4. Structural features called functionalgroups are the basis for classifying organiccompounds

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Organic vs. Inorganic Compounds

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IV. Acids – Nomenclature and Formula Writing

A. Binary Acids ( H+ + one other element)

B. Oxyacids (H+ + oxyanion)

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Which of the compounds C4H10, BaCl2, Ni(NO3)2, SF6 are expected to exist as molecules?

A) only C4H10

B) C4H10 and SF6

C) C4H10, Ni(NO3)2, and SF6

D) BaCl2 and Ni(NO3)2

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What is the charge on the Cr ions in Cr2O3?

A) 2-

B) 1+

C) 2+

D) 3+

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Identify a hydrocarbon.

A) CH3CH2OCH2CH3

B) CH3CH2OH

C) CH3CH2NH2

D) CH3CH2CH2CH3

E) CH3COOH

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Determine which formula/ name pair below is correct.

A. P2O5, phosphorus pentoxide

B. H2O, dihydrogen monoxide

C. NaNO3, monosodium nitrate

D. K2O, dipotassium monoxide

E. Fe2O3, iron(II) oxide

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V. Mass of Molecules

A. Mass of one molecule = formula mass(amu)

B. Molar mass – mass of one mole ofmolecules (grams)

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VII. % Composition of Compounds

A. % composition of the elementsin a compound can be determined from thechemical formula.

Example: Ammonium nitrate is commonlyused as a fertilizer. Calculate the mass % N inammonium nitrate.

B. % composition can be used as a conversion factor.Example: How much ammonium nitrate is needed to provide 1.00 lb of N?

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Example: Foodservice salt packets contain 0.50 g NaCl. Most Americans consume 3436 mg of sodium a day (more than twice the 1500 mg recommended maximum!). How many salt packets contain 3436 mg of sodium? NaCl is 39.0 % Na by mass.

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VII. Conversion Factors in Chemical Formulas

A. Conversion formulas can be constructedfrom chemical formulas.

B. Example: How many g of nitrogen are in5.00 lb of ammonium sulfate (another commonfertilizer)?

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VIII. Empirical and Molecular Formulas from Experimental Data

A.The mole ratios of elements in a compoundcan be determined from elemental analysis.

Example: Elemental analysis of a 15.0 g unknown sample gave the following results:

2.82 g Na, 4.35 g Cl, 7.83 g OUse the data above to determine the empirical formula of the compound.

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Example: Benzo[a]pyrene is a carcinogen found in coal dust, cigarette smoke,and charcoal grilled meats. Elemental analysis gave the following results.

95.21 % C4.79 % H

1.Determine the empirical formula for benzo[a]pyrene.

2. If the molar mass of benzo[a]pyrene is 252.30 g/mol, what is the molecular formula?

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B. Combustion Analysis of a Compound

1. What is combustion?

2. Combustion analysis is used to determinethe empirical formula of a compound.

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3. Examples

a. Combustion analysis of a hydrocarbon produced 33.01 g CO2 and 13.51 g H2O. Calculate the empirical formula for thehydrocarbon.

What is the molecular formula given the molarmass of the hydrocarbon is 42.09?

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b. Vitamin C (MM = 176.12 g/mol) is a compoundof C, H, and O found in many natural sources, especially citrus fruits. When a 1.000 g sampleof vitamin C is placed in a combustion chamberand burned, the following data are collected.

1.50 g CO2

0.41 g H2OUse the data above to determine the empiricalformula and molecular formula for vitamin C.

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IX. Chemical Equations

A. Chemical equations summarizechemical changes.

B. Characteristics of a chemical equation to know

• chemical formulas • reactants and products • state symbols • coefficients • balanced equation

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c. Practice

1.When aluminum metal reacts with air, it produces a white, powdery compound, aluminum oxide.

2. Gaseous carbon monoxide reacts withhydrogen gas to form gaseous methane and liquid water.

3. Write the reaction for the complete combustionof pentane.

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__ C3H5N3O9 __ N2 + __ CO2 + __ H2O + __ O2

What are the coefficients for the decomposition of nitroglycerin?

A. 2,3,6,2,1

B. 2,3,6,5,1

C. 4,6,12,10,12

D. 4,3,12,10,1

E. 4,6,12,10,1

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Calculate the number of carbon atoms in 25.0 grams of isopropyl alcohol (C3H8O).

A) 1.25 C atoms

B) 15.0 C atoms

C) 2.51 x 1023 C atoms

D) 7.52 x 1023 C atoms

D) 2.07 x 10–24 C atoms

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An unknown compound contains the following percents by mass: C: 60.86%, H: 5.83%, O: 23.16%, and N: 10.14%. Find the empirical formula.

A) C6H8O2N2

B) C7H8O2N

C) C6H8O2N

D) C8H8O2N

E) C8H8ON