chapter 5 chemical bonding and states of matter. by the end of the chapter, you will recognize that...

Chapter 5

Chemical Bonding and States of Matter

By the end of the chapter, you will recognize that

a. Having eight valence electrons is particularly desirable (“the octet rule”).

b. Atoms form bonds with other atoms to satisfy the octet rule.

c. The two major types of chemical bonds are ionic and covalent.

Chapter Learning Objectives

Chapter Learning Objectives (cont)

d. Electronegativity is the ability to attract shared electrons.

e. The type of bond formed between two atoms depends on their difference in electronegativity.

f. Ionic bonds form between atoms with a large difference in electronegativity (generally a metal and a nonmetal).


g. Nonpolar covalent bonds form between atoms with little difference in electronegativity (generally two nonmetals).

h. Polar covalent bonds form between atoms with intermediate difference in electronegativity.

i. Like dissolves like. That is, polar solutes dissolve in polar solvents.


j. Intermolecular forces hold the molecules of a material together in different states of matter.

k. Stronger intermolecular forces lead to higher melting and boiling temperatures.

l. The relative strengths of intermolecular forces generally follow the trend:

hydrogen bonds > dipole-dipole interactions > London forces

Chapter Outline

A. The Octet Rule The noble gases of Group VIIIA do not

typically form compounds with other atoms. Atoms with eight valence electrons are

particularly stable, an observation called the octet rule.

Atoms form bonds with other atoms to achieve a valence octet.

& B.

An octetis 8 valence electrons.is associated with the stability of the noble gases.

He is stable with 2 valence electrons (duet).

valence electrons

He 2 2

Ne 2, 8 8

Ar 2, 8, 8 8

Kr 2, 8, 14, 8 8

Octet Rule

ElectronicConfiguration of Noble Gases

Chapter Outline

C. Types of compounds

1. Ionic Attractions between oppositely charged

particles

2. Covalent Atoms share electron pairs.

Types of Compounds

Chapter Outline

Lewis Dot Structures (Review) The number of valence electrons is equal to the

group number for most of the main group elements.

In Lewis dot structures, the chemical symbol represents the nucleus and the core electrons and dots represent the valence electrons.

Lewis Dot Structures

Chapter Outline

1. Ionic Bonds Ionic compounds result from the loss of

electrons by one atom (usually a metal) and the gain of electrons by another atom (usually a nonmetal).

Ionic bonds arise from the attraction between particles with opposite charges (electrostatic forces); e.g., Na+ Cl-.

Ionic and Covalent Bonds

Atoms form octets

to become more stable.

by losing, gaining, or sharing valence electrons.

by forming ionic bonds or covalent bonds.

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

:

Metals Form Positive Ions known as CationsMetals form positive ions (cations)

by a loss of their valence electrons.

with the electron configuration of the nearest noble gas.

that have fewer electrons than protons.

Group 1A metals ion 1+




Formation of a Sodium Ion, Na+

Sodium achieves an octet by losing its one valenceelectron.


2, 8, 1 2, 8

Charge of Sodium Ion, Na+

With the loss of its valence electron,the sodium ion has a +1 charge.

Sodium atom Sodium ion 11p+ 11p+

11e- 10e-

0 1+


2, 8

Learning CheckA. The number of valence electrons in aluminum is

1) 1e-. 2) 2e-. 3) 3e-.

B. The change in electrons for octet requires a

1) loss of 3e-. 2) gain of 3e-. 3) a gain of 5e-.

C. The ionic charge of aluminum is

1) 3-. 2) 5-. 3) 3+.

D. The symbol for the aluminum ion is

1) Al3+. 2) Al3-. 3) Al+.

Solution A. The number of valence electrons in aluminum is

3) 3 e-.

B. The change in electrons for octet requires a1) loss of 3e-.

C. The ionic charge of aluminum is3) 3+.

D. The symbol for the aluminum ion is1) Al3+.

Formation of Negative Ions known as AnionsIn ionic compounds, nonmetals

achieve an octet arrangement.

gain electrons.

form negatively charged ions with 3-, 2-, or 1- charges.

Formation of a Chloride, Cl-

Chlorine achieves an octet by adding an electron to its valence electrons.

2, 8, 7 2, 8, 8


Charge of a Chloride Ion, Cl-

By gaining one electron, the chloride ion has a -1 charge.

Chlorine atom Chloride ion

17p+ 17p+

17e- 18e-

0 1–


Some Ionic Charges

I-


A. The number of valence electrons in sulfur is

1) 4e-. 2) 6e-. 3) 8e-.


1) loss of 2e-. 2) gain of 2e-. 3) a gain of 4e-.

C. The ionic charge of sulfur is

1) 2+. 2) 2-. 3) 4-.

Learning Check

A. The number of valence electrons in sulfur is

2) 6e-.


2) gain of 2e-.

C. The ionic charge of sulfur is

2) 2-.

Solution

The balance of charges in Al2O3

Run the following web animations/movies.

5.1: Formation of Sodium Chloride

5.2: Sodium Metal Reacting with Chlorine Gas

5.3: Ion Formation

Ionic Compounds

Naming Ionic Compounds with Two Elements To name a compound

that contains two elements,

• identify the cation and anion.

• name the cation first followed by the name of the anion.

Charges of Representative Elements


Names of Some Common Ions

•


Complete the names of the following ions. Ba2+ Al3+ K+

_________ __________ _________

N3 O2 F

_________ __________ _________

P3 S2 Cl

_________ __________ _________

Learning Check

Ba2+ Al3+ K+

barium aluminum potassium

N3 O2 F

nitride oxide fluoride

P3 S2 Cl

phosphide sulfide chloride

Solution

Formula Ions Name

cation anion

NaCl Na+ Cl- sodium chloride

K2S K+ S2- potassium sulfide

MgO Mg2+ O2- magnesium oxide

CaI2 Ca2+ I- calcium iodide

Al2O3 Al3+ O2- aluminum oxide

Examples of Ionic Compounds with Two Elements

Write the names of the following compounds.

1) CaO ___________

2) KBr ___________

3) Al2O3 ___________

4) MgCl2___________

Learning Check

Write the names of the following compounds:

1) CaO calcium oxide

2) KBr potassium bromide

3) Al2O3 aluminum oxide

4) MgCl2 magnesium chloride

Solution

A polyatomic ion • is a group of atoms. • has an overall ionic charge.

Some examples of polyatomic ions are

NH4+ ammonium OH− hydroxide

NO3−

nitrate NO2−

nitrite

CO32− carbonate PO4

3− phosphate

HCO3− hydrogen carbonate

(bicarbonate)

Polyatomic Ions

Some Compounds with Polyatomic Ions


The names of common polyatomic anions

• end in ate.

NO3− nitrate PO4

3− phosphate

• with one oxygen less end in ite.

NO2− nitrite PO3

3− phosphite

• with hydrogen attached use the prefix hydrogen (or bi).

HCO3− hydrogen carbonate (bicarbonate)

HSO3− hydrogen sulfite (bisulfite)

Some Names of Polyatomic Ions

Names and Formulas of Common Polyatomic Ions


• The positive ion is named first followed by the name of the polyatomic ion.

NaNO3 sodium nitrate

K2SO4 potassium sulfate

Fe(HCO3)3 iron(III) bicarbonate

or iron(III) hydrogen carbonate

(NH4)3PO3 ammonium phosphite

Naming Compounds with Polyatomic Ions

Chapter Outline2. Covalent Bonds

Covalent bonds are formed when two atoms share one or more electron pairs.

A molecule is the fundamental unit of a covalent compound.

When two atoms share one pair of electrons, the result is a single bond.

Two shared pairs of electrons is a double bond; three is a triple bond.

Covalent bonds form

• when atoms share electrons to complete octets.

• between two nonmetal atoms.

• between nonmetal atoms from Groups 4A(14), 5A(15), 6A(16), and 7A(17).

Covalent Bonds

Hydrogen Molecule

A hydrogen molecule

• is stable with two electrons (helium).

• has a shared pair of electrons.


5.4: Bond Length and Energy

5.5: Electrostatic Interactions Between Hydrogen Atoms

Forming Octets in Molecules

In a fluorine, F2,, molecule, each F atom

• shares one electron.

• attains an octet.

Carbon forms 4 covalent bonds

In a CH4, methane, molecule

• a C atom shares 4 electrons to attain an octet.

• each H shares 1 electron to become stable like helium.

Multiple Bonds

In nitrogen molecule, N2,

• each N atom shares 3 electrons.• each N attains an octet.• the bond is a multiple bond called a triple bond.• the name is the same as the element.

Naming Covalent Compounds

To name covalent compounds• STEP 1: Name the first

nonmetal as an element.

• STEP 2: Name the second nonmetal with an ide ending.

• STEP 3: Use prefixes to indicate the number of atoms (subscript) of each element.

Table5.12

What is the name of SO3?

1. The first nonmetal is S sulfur.

2. The second nonmetal is O named oxide.

3. The subscript 3 of O is shown as the prefix tri.

SO3 sulfur trioxide

The subscript 1 (for S) or mono is understood.


Name P4S3.

1. The first nonmetal P is phosphorus.

2. The second nonmetal S is sulfide.

3. The subscript 4 of P is shown as tetra.

The subscript 3 of S is shown as tri.

P4S3 tetraphosphorus trisulfide


Formulas and Names of Some Covalent Compounds


Select the correct name for each compound.

A. SiCl4 1) silicon chloride

2) tetrasilicon chloride3) silicon tetrachloride

B. P2O5 1) phosphorus oxide

2) phosphorus pentoxide3) diphosphorus pentoxide

C. Cl2O7 1) dichlorine heptoxide

2) dichlorine oxide3) chlorine heptoxide

Learning Check

Select the correct name for each compound.

A. SiCl4 3) silicon tetrachloride

B. P2O5 3) diphosphorus pentoxide

C. Cl2O7 1) dichlorine heptoxide

Solution

Covalent bonds are subclassified as nonpolar or

polar

Predicting Compounds using Lewis Dot Structures Going back to the idea of Lewis dot

configuration as a good way to keep track of valence electrons for predicting structure of ionic/covalent compounds.

Ionic Compounds Magnesium Iodide using the crossover method to

determine the molecular formula and draw the structure using Lewis dot valence electrons.

Step 1: Forming the magnesium cation:

Mg2+Mg + 2e-

Step 2: Forming the iodide anion:

I + 1e- I

Step 3: Putting the ions together

We need 2 iodide anions to balance the +2 charge on the magnesium, as indicated by the formula MgI2

IMg2+I

Covalent Compounds

Covalent compounds between oxygen and hydrogen

Step 1: Determine how many bonds are formed by oxygen

Step 2: Determine how many hydrogen atoms are in the chemical formula (hydrogen forms a single bond)

Step 3: Draw the structure

Draw the structure for H2O

O6 valence e- 2 max bonds

O H

H

O H2

6 valence e-

and

1 valence e-H2O

H1 valence e- 1 bond each

Covalent Compounds

Covalent compounds between carbon and hydrogen

Step 1: Determine how many bonds are formed by carbon

Step 2: Determine how many hydrogen atoms are in the chemical formula (hydrogen forms a single bond)

Step 3: Draw the structure

Draw the structure for CH4

H1 valence e- 1 bond each

4 valence e- 4 max bondsC

H4

4 valence e-

and

1 valence e-

CH4

C H

H

C

H

H

Chapter Outline

d. Equal Sharing versus Unequal Sharing When two different kinds of atoms are bonded,

the electrons are usually shared unequally. When a bond exists between two identical kinds

of atoms, the electrons are shared equally. An atom with greater electronegativity has a

greater ability to attract shared electrons.

Electronegativity

Chapter Outline

d. Equal Sharing versus Unequal Sharing (cont)

The greater the difference in electronegativity between two atoms that are covalently bonded, the more polar is the bond.

Polar vs. Nonpolar Bonds

Paired molecules much different in electronegativity play tug of war

Credit: Courtesy of Julie Millard

Chapter Outline

j. States of Matter Review of Types of Bonds

1. Chemical bonds (intramolecular forces) hold atoms together.

2. The three types of chemical bonds are ionic, polar covalent, and nonpolar covalent.

3. Intermolecular forces hold molecules together.

Types of Bonds

Chapter Outline

j. States of Matter (cont) Particle Cohesion Determines Physical State

1. In general, the relative strengths of intermolecular forces follows the trend:

gases < liquids < solids Changes of State

Adding energy breaks intermolecular forces and causes molecules to change their state.

The stronger the intermolecular forces of a compound, the higher are the melting and boiling points.

Changes of State

Chapter Outlinek. Types of Intermolecular Forces within

Pure Substances London dispersion forces

A temporary dipole in one molecule can induce a dipole in a neighboring molecule.

The negative end of one temporary dipole can attract the positive end of an induced dipole; these attractions are called London dispersion forces.

London forces tend to be fairly weak.

Instantaneous dipoles from electron movements

London Dispersion Forces

Chapter Outline

Types of Intermolecular Forces within Pure Substances (cont) Dipole-dipole interactions

Dipole-dipole interactions exist between molecules with polar covalent bonds.

Dipole-dipole interactions are typically stronger than London dispersion forces.

Dipole-Dipole Interactions

Chapter Outline Types of Intermolecular Forces within

Pure Substances (cont) Hydrogen Bonds

Hydrogen bonds are a special type of dipole-dipole interaction.

Hydrogen bonds can occur when H is bonded to one of the highly electronegative atoms N, O, or F. An example is H2O.

Hydrogen bonds are typically quite strong.

Hydrogen Bonds in Water

Ice crystal lattice


5.6: Electric Current Conduction by Molten Salts

5.8a: Atomic Motion and Thermal Energy

5.9: Atomic Properties of Solids, Liquids, and Gases

Chapter Outline

i. Forming Solutions Like dissolves like

Ionic solutes often dissolve in polar solvents;e.g., NaCl dissolves in H2O.

Polar solutes generally dissolve in polar solvents; e.g., NH3 in H2O.

Nonpolar solutes generally do not dissolve well in polar solvents; e.g., oil in H2O.


5.10: Like Dissolves Like Solubility

NaCl Dissolving in H2O

Polar covalent molecules with dipoles can induce dipoles in nonpolar molecules

Why octane molecules and water don't mix

Oil and water do not mix

Credit: Visuals Unlimited

Chapter Outline

Emulsions Emulsifying agents are molecules that contain a

polar portion and a nonpolar region. Soap is an example of an emulsifying agent that

can form a suspension of a nonpolar material in a polar solvent (an “emulsion”).

Emulsification with Soap

Chapter Outlinel. Measuring Amounts in Solution

Solubility The maximum amount of a solute that dissolves in a

solvent Molarity

The amount of a solute dissolved in a solvent is its concentration.

Concentration is often measured in moles/liter, also called molarity (M).

Parts per million (ppm) The concentration of a dilute solution may be measured

in parts per million (grams of solute per million grams solution).

Solubilities of various Ionic Compounds in Water

Key Words

Chemical bonds Noble gases Octet rule Ionic compound Ion Covalent compound Lewis dot structures Core electrons Cation Anion Electrostatic forces

Chemical formula Lone pair Single bond Double bond Triple bond Isomers Nonpolar covalent bond Polar covalent bond Electronegativity Dipole Structure

Key Words

Intermolecular forces London dispersion forces Dipole-dipole interactions Hydrogen bonds Solution Solute Solvent Aqueous solution

Colloid Suspension Amphiphilic/

amphipathic Emulsion Solubility Concentration Molarity (M) Parts per million (ppm)

chapter 5 chemical bonding and states of matter. by the end of the chapter, you will recognize that...

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atoms form bonds

ionic bonds form

covalent atoms

octet rule slide

number of valence electrons

valence octet

valence electrons duet

ionic bonds ionic compounds