Chapter 5. Some types of chemical reactions Objectives:

Describe the periodic table and some of the relationships that it summarizes

Recognize and descibe nonelectrolytes, strong and weak electrolytes.

Recognize and classify acids, bases, and salts

Assign oxidation number to elements, when they are free, in compounds, or in ions

Objectves (continue) Name and write formulas for

common binary and ternary inorganic compounds

Recognize oxidation-reduction reactions and identify which species are oxidized, reduced, oxidizing agents, and reducing agents

Recognize and describe classes of reactions

The periodic table: metals, nonmetals, and metalloids

Help predict and explain the properties of elements (function of number of protons and electrons)

Electrons in the outermost shell are called valance electrons (valance shell) chemical bonding

Atomic weight (orginated from mass number)

Periodic table Atomic number of an element is

the number of protons in the nucleus of its atoms

Elements are arranged in the periodic table in order of increasing atomic number.

The properties of the elements are periodic functions of their atomic number

Metallic character decrease

Increase

Transition metals

Noble gases

The vertical colums are referred to as groups or families

The horizontal rows are called periods

Elements in a group have similar chemical and physical properties, and those within a period have properties that change progressively across the table.

Names of some common groups The Group IA elements (except H)

are referred to as alkaline metals The Group IIA elements are called

alkaline earth metals The Group VIIA elements are called

halogens (“salt formers”) The Group VIIIA elements are

called noble (rare) gases

Some physical properties of metals and nonmetals

Metals High EC that

decreases with increasing temperature

High thermal conductivity

Metallic gray or silver luster

Almost all are solids Malleable Ductile

Nonmetals Poor electrical

conductivity (except C in graphite)

Good heat insulator No metallic luster Solids, liquids, or

gases Brittle in solid state Nonductile

Some chemical properties of metals and nonmetals

Metals Outermost shells

contain few electrons (usually 3 or fewer)

Form cations by losing electrons

Form ionic compounds with nonmetals

Solid state characterized by metallic bonding

Nonmetals Outermost shells

contain 4 or more electrons

Form anions by gaining elecrtons

Form ionic compounds with metals, and molecular (covalent) other compounds with nonmetals

Covalently bonded molecules

Metalloids (semi-metals) show some properties that are characteristic of both metals and nonmetals

Example: B, Si, Ge, As, Te Many of the metalliods, such as Si, Ge, and

Sb act as semiconductors (for electronic curcuits). Semiconductor are insulators at lower temperatures but become conductors at higher temperatures.

Aqueous solutions Solutes that are water-soluble can

be classified as either electrolytes or nonelectrolytes

Electrolytes are substances whose aqueous solutions conduct electric current.

Aqueous solution of nonelectrolytes do not conduct electricity

Dissociation refers to the process in which a solid ionic compound, such as NaCl(s), separates into its ions in solution

Ionization refers to the process in which a molecular compound separates or reacts with water to form ions in solution (HCl (g))

Three major classes of solutes are strong electrolytes

(1) strong acids, (2) strong bases, and (3) most soluble salts

These compounds are completely or nearly completely ionized (or dissociated) in dilute aqueous solutions

An acid: a substance that produces hydrogen ions, H+, in aqueous solutions

A base: a substance that produces hydroxide ions, OH-, in aqueous solutions

A salt: is a compound that contains a cation other than H+ and anion other than hydroxide ion, OH-, or oxide ion, O2-

Some strong acids and their anions

Common strong acids HCl HBr HI HNO3

HClO4

HClO3

H2SO4

Anions of these acids Cl-

Br-

I-

NO3-

ClO4- :

ClO3-:

HSO4-

SO4-

Some common weak acids and their anions

Common weak acids HF CH3COOH HCN HNO2

H2CO3

H2SO3

H3PO4

Anions of these acids F-

CH3COO-

CN-

NO2-

HCO3-

CO32-

__

Reversible reactions

Reactions that occur in both directions

Examples HCl no reversible reaction H+(aq) + CH3COO-(aq)

CH3COOH(aq)

Common strong bases Group IA

LiOH NaOH KOH RbOH CsOH

Group IIA

Ca(OH)2

Sr(OH)2

Ba(OH)2

Insoluble bases & weak bases

Isoluble bases: Cu(OH)2, Zn(OH)2, Fe(OH)2 and Fe(OH)3

Weak bases: NH3 and closely related N-containing compounds, the amines,

Reactions in aqueous solutions

Formula unit equations (stoichiometric calculation)

Total ionic equations Net ionic equations (show only the

species that react: essence of a chemical reaction)

AgNO3(aq) + Cu(s) Ag(s) + Cu(NO3)2 (aq)

[ ] [ ]

Oxidation number Many reactions that involve the transfer of

electrons from one species to another are called oxidation-reduction reactions (redox reactions)

We use oxidation numbers to keep track of electron transfers.

The oxidation number of an element in a simple binary ionic compound is the number of electrons gained or lost by an atom of that element when it forms the compound

Some rules for assigning oxidation numbers

H2, O2 (oxidation number is zero) Ca2+ (oxidation number is +2) NaCl (the sum of the oxidation

numbers of all atoms in a compound is zero)

SO42- (polyatomic ions) (the sum is -2)

F has an oxidation number of -1 in its compound

H has an oxidation number of +1 in compounds unless it is combined with metals (NaH, CaH2) its oxidation number is -1.

Oxygen usually has an oxidation number of -2 in its compounds (some exceptions: peroxides, H2O2 (-1); superoxides, KO2 (-1/2); OF2 (+1/2))

The position of the element in the periodic table helps to assign its oxidation number:

Example

Determine the oxidation number of N in the following species:

(a) N2O4, (b) NH3, (c)HNO3, (d) NO3-,

(e) N2

Naming some inorganic compounds

Naming binary compounds: binary compounds consist of two elements

Binary ionic compounds The cation is named first and the anion

second The oxidation number of the metal is

indicated by a Roman numeral (IUPAC) An older method, still in use, uses “-

ous” and “ic” suffixes to indicate lower and higher oxidation numbers, respectively. This system can distinguish between only two different oxidation numbers for a metal.

Examples

CuCl CuCl2 FeO FeBr3

Hg2Cl2 HgCl2

Binary molecular compounds

Using prefix system for both elements

The prefixes are: mono-, di-, tri-, tetra...

Examples N2O4, Cl2O7, CS2, SF4, SF6

Binary acids

HCl(g), (aq) HF(g), (aq) H2S(g), (aq) HCN(g), (aq)

Naming ternary acids and their salts

A ternary compound consists of 3 elements

Ternary acids (oxoacids) are compounds of hydrogen, oxygen and a nonmetal. Nonmetals that have more than one oxidation number form more than one ternary acid (Ex. H2SO4, H2SO3)

Formulas of some common “-ic” acid

Group IIIA: H3BO3 (boric acid) Group IVA: H2CO3 (carbonic acid), H4SiO4

(silicic acid) Group VA: HNO3 (nitric acid), H3PO4

(phosphoric acid), H3AsO4 (arsenic acid) Group VIA: H2SO4, H2SeO4 (selenic acis),

H6TeO6 (telluric acid) Group VIIA: HClO3 (chloric acid), HBrO3,

HIO3

In case one or more acidic hydrogen atoms remain

Use the word “hydrogen” or “dihydrogen” to show the number of

Example: Name the following compounds

NaHSO4, NaHSO3, KH2PO4, K2HPO4, NaHCO3

Name the followings

Oxidation number Name

HClO4 +7 per- HClO3 +5 chloric

acid HClO2 +3 chlorous HClO +1 hypo-

Naming ternary acids and their anions

Ternary acid perXXXic acid XXXic acid XXXous acidhypoXXXous acid

Anion perXXXate XXXate XXXite hypoXXXite

Decreasing oxidation number of central atom Decreasing number of oxygen

atoms on central atom

Classifying chemical reactions

1. Oxidation-reduction reactions2. Combination reactions3. Decomposition reactions4. Displacement reactions5. Metathesis reactions

Oxidation-reduction reaction

Oxidation is an increase in oxidation number and corresponds to the loss of electrons. Reduction is a decrease in oxidation number and corresponds to a gain of electrons.

Oxidation and reduction occur simultaneously. (In brief, the reaction is called redox reaction)

Ex: Fe(s) + O2(g) Fe2O3(s)

Oxidizing and reducing agents

Oxidizing1. Oxidize other

substances2. Contain atoms that

are reduced3. Gain electrons

Reducing1. Reduce other

substances2. Contain atoms that

are oxidized3. Lose electrons

ExampleFe(s) + Cl2 FeCl3

Redox reaction

Disproportionation reaction is a redox reaction in which the same element is oxidized and reduced

ExampleCl2 + H2O HCl + HClO

Combination reactions

Reactions in which two or more substances combine to form a compound are called combination reactions

Example Mg + F2 MgF2

Combination reactions Element + Element CompoundNa(s) + Cl2(g) NaCl(s) (metal + nonmetal)

P4 + Cl2 PCl3 (nonmetal + nonmetal) Compound + Element CompoundPCl3(l) + Cl2(g) PCl5(s) Compound + Compound CompoundCaO(s) + H2O (l) Ca(OH)2 (aq)

Decomposition reactions

Decomposition reactions are those in which a compound decomposes to produce (1) two elements, (2) one or more element and one or more compounds, (3) two or more compounds

Example CaCO3(s) CaO(s) + CO2(g)

Decomposition reaction

Compound Element + Element Compound Compound +

Element Compound Compound +

Compound

Displacement reactions

Reactions in which one element displaces another from a compound are called displacement reactions

ExampleZn(s) + CuSO4(aq) Cu(s) +

ZnSO4(aq)

Displacement reaction [More active metal + salt of less active metal]

[Less active metal + salt of more active metal] [Active metal + nonoxidizing acid] [Hydrogen +

salt of acid]H2SO4 (should be in very dilute solution) [Active nonmetal + salt of less active nonmetal]

[Less active nonmetal + salt of more active nonmetal]Each halogen will displace less active (heavier) halogens

F2>Cl2>Br2>I2

Metathesis reactions

In many reactions between two compounds in aqueous solution, the positive and negative ions appear to “change partners” to form two new compounds, with no change in oxidation number. Such reactions are called metathesis reactions

Example AgNO3(aq)+NaCl(aq) AgCl(s)+NaNO3(aq)

Metathesis reactions

Acid-base (neutralization) reactions: formation of nonelectrolyte

HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)

Precipitation reactions

Exercise Assign oxidation numbers to the

element specified in each group of ions

(a) P in PCl5, P4O6, P4O10, HPO3, H3PO3, POCl3, H4P2O7, Mg3(PO4)2

(b) Mn in MnO, MnO2, Mn(OH)2, K2MnO4, KMnO4, Mn2O7.

(c) O in OF2, Na2O, Na2O2, KO2

Exercise Write each of the following formula unit equations

as net ionic equation if the two differ? For the redox reactions, identify the oxidizing agent, the reducing agent, the species oxidized and the species reduced

(a) AgNO3(aq) + Cu(s) Cu(NO3)2(aq) + Ag(s)

(b) KClO3(s) KCl(s) + KClO4

(c) AgNO3(aq) + K3PO4(aq) Ag3PO4(s) + KNO3(aq)

heat

Exercise

Balancing and Classifying reactions(a) Zn(s) + AgNO3(aq) Zn(NO3)2(aq) + Ag(s)

(b) Ca(OH)2(s) CaO(s) + H2O(g)

(c) HI(g) H2(g) + I2(g)

(d) Cu(NO3)2(aq) + Na2S(aq) CuS(s) + NaNO3(aq)

(e) SO2(g) + H2O(l) H2SO3(aq)

(f) H2SO3(aq) + KOH(aq) K2SO3(aq) + H2O(l)

heat

heat

Write the chemical formula or name of the following compounds