Hoa dai cuong_chuong 3

Philip Dutton
University of Windsor, Canada

Prentice-Hall © 2002


Chapter 3: Chemical Compounds
General Chemistry
Principles and Modern Applications
Petrucci • Harwood • Herring
8th Edition
Contents
3-1 Molecular and Ionic Compounds
3-2 Molecular Mass
3-3 Composition
3-4 Oxidation States
3-5 Names and formulas
Focus on Mass Spectrometry


Molecular compounds
1 /inch
0.4 /cm
Standard color scheme
Some molecules
Ionic compounds
Atoms of almost all elements can gain or lose electrons to form charged species called ions.
Compounds composed of ions are known as ionic compounds.

Metals tend to lose electrons to form positively charged ions called cations.
Non-metals tend to gain electrons to form negatively charged ions called anions.
Sodium chloride
Extended array of Na+ and Cl- ions Simplest formula unit is NaCl
Inorganic molecules
Molecular mass
Molecular formula C6H12O6
Empirical formula CH2O
Glucose
Halothane C2HBrClF3
Chemical Composition
Mole ratio nC/nhalothane
Mass ratio mC/mhalothane
Example 3.4
Calculating the Mass Percent Composition of a Compound
Calculate the molecular mass
M(C2HBrClF3) = 197.38 g/mol
For one mole of compound, formulate the mass ratio and convert to percent:

Example 3-4
Empirical formula
Choose an arbitrary sample size (100g).
Convert masses to amounts in moles.
Write a formula.
Convert formula to small whole numbers.
Multiply all subscripts by a small whole number to make the subscripts integral.



5 Step approach:
Determining the Empirical and Molecular Formulas of a Compound from Its Mass Percent Composition.
Dibutyl succinate is an insect repellent used against household ants and roaches. Its composition is 62.58% C, 9.63% H and 27.79% O. Its experimentally determined molecular mass is 230 u. What are the empirical and molecular formulas of dibutyl succinate?
Step 1: Determine the mass of each element in a 100g sample.
C 62.58 g H 9.63 g O 27.79 g
Dibutyl succinate is an insect repellent used against household ants and roaches. Its composition is 62.58% C, 9.63% H and 27.79% O. Its experimentally determined molecular mass is 230 u. What are the empirical and molecular formulas of dibutyl succinate?

Example 3-5
Step 2: Convert masses to amounts in moles.
Step 3: Write a tentative formula.
Step 4: Convert to small whole numbers.
C5.21H9.55O1.74
C2.99H5.49O
Example 3-5
Step 5: Convert to a small whole number ratio.
Step 6: Determine the molecular formula.
Example 3-5
Combustion analysis
Oxidation States
Metals tend to lose electrons.
Na  Na+ + e-
Non-metals tend to gain electrons.
Cl + e-  Cl-
We use the Oxidation State to keep track of the number of electrons that have been gained or lost by an element.
Rules for Oxidation States
The oxidation state (OS) of an individual atom in a free element is 0.

The total of the OS in all atoms in:
Neutral species is 0.
Ionic species is equal to the charge on the ion.

In their compounds, the alkali metals and the alkaline earths have OS of +1 and +2 respectively.

In compounds the OS of fluorine is always –1


Rules for Oxidation States

In compounds, the OS of hydrogen is usually +1

In compounds, the OS of oxygen is usually –2.

In binary (two-element) compounds with metals:
Halogens have OS of –1,
Group 16 have OS of –2 and
Group 15 have OS of –3.


Assigning Oxidation States.
What is the oxidation state of the underlined element in each of the following? a) P4; b) Al2O3; c) MnO4-; d) NaH
P4 is an element. P OS = 0
Al2O3: O is –2. O3 is –6. Since (+6)/2=(+3), Al OS = +3.
MnO4-: net OS = -1, O4 is –8. Mn OS = +7.
NaH: net OS = 0, rule 3 beats rule 5, Na OS = +1 and H OS = -1.

Example 3-7
Naming Compounds
Trivial names are used for common compounds.

A systematic method of naming compounds is known as a system of nomenclature.

Organic compounds
Inorganic compounds
Inorganic Nomenclature
Binary Compounds of Metals and Nonmetals
NaCl = sodium chloride
name is unchanged
“ide” ending
electrically neutral
MgI2 = magnesium iodide
Al2O3 = aluminum oxide
Na2S = sodium sulfide

Binary Compounds of Two Non-metals
Molecular compounds
usually write the positive OS element first.
HCl hydrogen chloride

Binary Acids
Acids produce H+ when dissolved in water.
They are compounds that ionize in water.
Polyatomic Ions
Polyatomic ions are very common.
Table 3.3 gives a list of some of them. Here are a few:
ammonium ion NH4+ acetate ion C2H3O2-
carbonate ion CO32- hydrogen carbonate HCO3-
hypochlorite ClO- phosphate PO43-
chlorite ClO2- hydrogen phosphate HPO42-
chlorate ClO3- sulfate SO42-
perchlorate ClO4- hydrogensulfate HSO4-
Naming Organic Compounds
Organic compounds abound in nature
Fats, carbohydrates and proteins are foods.
Propane, gasoline, kerosene, oil.
Drugs and plastics
Carbon atoms form chains and rings and act as the framework of molecules.
Visualizations of some hydrocarbons
Visualizations of some hydrocarbons
Isomers
Isomers have the same molecular formula but have different arrangements of atoms in space.
Functional Groups – carboxylic acid
Functional Groups - alcohol
Chapter 3 Questions
3, 5, 12, 24, 35, 46, 53, 61, 57, 73, 95, 97