Chapter 8: Basic Concepts of Chemical Bonding

Chapter 8: Basic Concepts of Chemical Bonding

• Why do TiCl4 and TiCl3 have different colors? ... different chemical properties? ... different physical states?

Chemical Bonding and Properties

• Difference in colors is due to differences in electronic configuration for TiCl3 and TiCl4

• Differences in chemical behavior are due to differences in the types of bonds

• Bond: forces that hold atoms together in molecules or ionic compounds.

Chemical Bonding• Types of bonds and types of substances

– Ionic

– Covalent

– Metallic

• The type of bond between atoms is partially responsible for the properties of the substance.

Why do atoms form bonds?

Draw orbital diagrams for each of the following elements• Ne

• Na

• Cl

• H

• O

Lewis Symbols and the Octet Rule

Lewis Symbols and the Octet Rule• Lewis Symbols:

The number of valence electrons available for bonding are indicated by unpaired dots.

Lewis Symbols

• These symbols are called Lewis symbols.

• We generally place the electrons on four sides of a square around the element symbol.

Lewis_symb.exe.lnk

Why do atoms form bonds?• Octet Rule

• Lewis Dot Diagrams

• Atoms tend to gain, lose, or share electrons in order to acquire a full set of valence electrons.

• Used to illustrate an atoms valence electrons

• Used to illustrate how electrons rearrange during chemical reactions

Na Xe P

Lewis Dot Practice

• O

• Te

• Ca

• Ba

• Ne

• I

• Cs

Ions and Ionic Compounds

• Ions are formed by adding or subtracting electrons from a neutral atom or molecule.

• Cation: positive charge (remove electrons) Na+

• Anion: negative charge (add electrons) Cl-

• Ions may be monatomic or polyatomic

03m07an1&203m07an1&2

Types of Ions• Monatomic ions

– Single atom ions• O 2-

• Na+

• Al3+

• Polyatomic ions– More than one atom ions

• NH4 +

• OH –

• SO4 2-

Predicting Ionic ChargesPredicting Ionic Charges

• Electron Counts of Stable Ions– Ions tend to have the same number of

electrons as the nearest noble gas.• Main group ions of a given element tend to

be different by two units of charge.• Transition metals are not as predictable, but

+2 and +3 are common.

ion_charges.exe

Main Group ElementsMain Group Elements

Note periodicity of charges

Transition ElementsTransition Elements• Not periodic; +2 and +3 common

• Oxoanions generally have the same charge as the simple anion of the same nonmetal.

Charges and Formulas of Oxoanions

Charges and Formulas of Oxoanions

Related to position in the periodic table; note exceptions for B, C, N

Polyatomic Ions

tend to reflectthe charge of the base element

Why do atoms form bonds?• Ionic bond

• Example– Lewis Dot

diagram

• A positively charged ion is attracted to a negatively charged ion.

• A transfer of electrons• Metal and a Non-Metal

• NaCl

Na Cl Na Cl

Why do atoms form bonds?

• Practice

• Mg, S

• Ca, Br

Metal Non-Metal

Formation of an Ionic Compound

Vd02_007.mov

Properties of Ionic BondsProperties of Ionic Bonds

• Ionic bonds are very strong, so separating ions requires much energy

• High melting points, boiling points• Crystals are hard and brittle• Electrical insulators when solid, electrical

conductors when molten or dissolved in water

• Demo:electric_pickle.mov

Electrical ConductivityElectrical Conductivity

Solid NaCl Liquid NaCl

03s11vd103s11vd1

Structure and PropertiesStructure and Properties

• Why are crystalline solids brittle, whereas metallic solids are malleable?

Structure and PropertiesStructure and PropertiesBrittleness

brittle2.mov

maleable2.mov

Examples of Ionic FormulasExamples of Ionic Formulas

• What is the formula of each of these compounds?

Writing Formulas for Ionic Compounds

• Crisscross Method

• ExampleCa and F

• Write the element symbols for the cation and anion, with the cation on the left and the anion on the right.

• Write each ion’s charge as a superscript.

• Crisscross the two charges moving them downward diagonally from one superscript to the other subscript.

Writing Formulas for Ionic Compounds

• Practice • Li and O

• Mg and O

• Ca and N

Chemical FormulasChemical Formulas

• Remember • Combine ions to obtain electrical neutrality

Ionic_Formula.exeIonic_Formula.exe

Naming Binary Ionic Fixed Charge Compounds

(Formula Name)

Formula Name

Example:

Li2O

1. Name the cation

2. Name the anion, changing the ending to ide

Lithium Oxygen + ide

Lithium Oxide

Naming Binary Ionic Compounds

Name Formula

Example:

Calcium Chloride

Ca +2 and Cl -1

CaCl2

1. Identify the ions involved

2. List the cation first and then the anion

3. Determine that charge of each ion involved

4. Balance the charges so the compound is neutral.

Naming Binary Ionic Compounds STOCK (Transitional Metals)

Formula Name

CoCl2

Example:

Cobalt II chloride

1. Name the cation

2. Determine the charge of the anion

3. Based on the anion, what charge does the cation need to make the compound neutral.

4. Write the cation charge in parenthesis as a roman numeral

5. Name the anion.

Naming Binary Ionic Compounds Stock (Name Formula)

Name Formula

Example:

Calcium Chloride

Copper(II) Oxide

1. List the cation first and then the anion

2. Give the cation the charge stated in the name (roman numeral)

3. Determine the charge of the anion

4. Balance the charges so the compound is neutral.

Ca +2 and Cl –1 CaCl2

Cu + 2 and O –2 CuO

Naming Ternary Molecular Structures

What is a Ternary Molecular Structure?

Example•MgSO4

Magnesium Sulfate

•CuSO4 Copper (II) Sulfate

•A molecule that has more than two elements.•A combination of a metal and a polyatomic ion.•Same rules as Binary Ionic/Stock but just name the polyatomic

• How do we distinguish between ionic and covalent compounds?

• What do you notice?

CompoundsCompounds

Nacl.pdb Ch4.pdb

Why do atoms form bonds?

• Covalent bond

• Shared pair of electrons between two atoms.

• Non-metal and Non-metal

Lewis Structures

• Lewis Structures A representation of a molecule that shows

how the valence electrons are arranged among

the atoms in the molecule

* G. N. Lewis

• Lewis Dot Examples

Why do atoms form bonds?

• Molecule

• Diatomic Molecules

• Super 7

• A group of atoms united by a covalent bond

• A few elements only exist as a pair of atoms never as a single lone atom

• Cl2, I2, F2, Br2, O2, H2, N2

Why do atoms form bonds?• Characteristics

of covalent bonds

• Single Bonds– Ex. H2

• Double Bonds– Ex. O2, H2CO

• Triple Bonds– Ex. N2, C2H2

• Can form multiple bonds satisfy the octet rule

• Two atoms share exactly one pair of electrons.

• Two pairs of electrons shared between two atoms.

• Three pairs of electrons are shared between atoms

Properties of Covalent BondsProperties of Covalent Bonds

• Solids are usually soft

• low melting points

• low boiling points

• Properties arise because molecules are not strongly held together

• Usually found with nonmetals

Structural Formulas

• Why do atoms form bonds?

• Specifies which atoms are bonded to each other

• Distinguish the difference between substances with the same molecular formula

• See models of different types: Why do we have different types of models?

Structural FormulasExamples

Structural Formulas

• A few Models

NH3

CO2

• How are the atoms connected?H2SO4

Co2.pdb

H2so4.pdb

Nh3.pdb

Lewis Structure for Super 7’s

• Draw Lewis structures for super 7’s

Chemical FormulasChemical Formulas

• S8, O2, O3 - What formulas do we find for elements? Elements with different formulas are called allotropes.

• How many atoms make a molecule? Is there any pattern?

xenon oxygen phosphorus sulfur ozone

nonmetals.exe.lnk

Naming Binary Covalent Compounds

Covalent compound

Definition

• Non-metal and non-metal• Share Electrons

Naming Binary Covalent Compounds

Prefixes 1= mono

2= di

3 = tri

4 = tetra

5 = penta

6 = hexa

7 = hepta

8 = octa

9 = nona

10 = deca

Naming Binary Covalent Compounds

PracticeName Formula

What is the formula for the following compounds?

1. Write the chemical formula of the first element listed.

2. Write the prefix number as a subscript.

3. Write the chemical formula of the second element listed.

4. Write the prefix number as a subscript.

a. Pentachlorine dioxideb. Carbon monoxidec. Tribromine hexasulfide

Naming Binary Covalent Compounds

Practice

FormulaName

What is the name of the following compounds?

1. Write the number of the first element as a prefix, add the name of chemical.

2. Write the number of the second element as a prefix, add the name of chemical and end in –ide.

a. P4C8

b. F9I6

c. SN3