Warm-upHow many valence electrons does each of the following atoms have? Draw a Bohr Diagram

for each element1. B2. F3. Ar4. Se5. Ba6. Si

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

Notes handout

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

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 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 Elements

Note periodicity of charges

Transition 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

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

Polyatomic Ions

tend to reflectthe charge of the base element

Practice on Ionic Charges

• Pair Share: What is the common charge of an ion of potassium, K?

• Pair Share: What is the common charge of an ion of sulfur, S?

• Pair Share: What is the common charge of an ion of iron, Fe?

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

What holds Ionic bonds together?

Formation of an Ionic Compound

Vd02_007.mov

Properties 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 Conductivity

Solid NaCl Liquid NaCl

03s11vd103s11vd1

Structure and Properties

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

Structure and PropertiesBrittleness

brittle2.mov

maleable2.mov

Examples 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

Practice

• Rewrite these incomplete formulas as correct formulas. AlS CaP BaBr

• Make formulas from the following ions: Fe2+, PO4

3- Sc3+, O2-

Bonding with a partner

• You will receive a card with an ion. • You will find another person with the

opposite charge from you. • You will write the ions on your paper and

the formula they will create together.• Exchange cards and repeat the steps again

until you fill up your paper.

Chemical 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 cation2. Name the anion, changing the

ending to ide

Lithium Oxygen + ideLithium Oxide

Naming Binary Ionic CompoundsName Formula

Example: Calcium ChlorideCa +2 and Cl -1CaCl2

1. Identify the ions involved2. List the cation first and then

the anion3. Determine that charge of each

ion involved4. Balance the charges so the

compound is neutral.

Practice

Write the structural formula for the following:

Hint: separate them into ions and then criss cross

Magnesium phosphide

Calcium iodide

Beryllium oxide

Naming Binary Ionic Compounds STOCK (Transitional Metals)

Formula Name

CoCl2

Example:Cobalt II chloride

1. Name the cation 2. Determine the charge of the

anion3. 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 ChlorideCopper(II) Oxide

1. List the cation first and then the anion

2. Give the cation the charge stated in the name

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

Practice

• Writing Formulas “Transition Metals (stock Method)” wksheet

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

Rally Table

• NaF• K2CO3

• MgCl2

• Be(OH)2

Practice Worksheet

Brain Teaser

• Write the formula for the following elements: Potassium and Phosphorus

• Name the following compounds• SrS• Cu2S• Iron (II) oxide• Lithium cyanide

• How do we distinguish between ionic and covalent compounds?

• What do you notice?

Compounds

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

Round Table – Covalent Bonding

• SiH4

• NH41+

• H2Se• HCl• HF• *SO4

2-

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 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

Worksheet:

• Draw Lewis Dot structures for the following molecules

Chemical 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

Brain Teaser

• Write the Lewis structure for each of the following simple molecules.

• H2S

• C2H4

• SiF4

Shapes Lab• Work with a partner • Draw the Lewis Dot Diagrams for each of

the compounds• Build each of the compounds using the

model kits.• Sketch the shape of the model

– Remember all the holes (bonding sites) of each atom must be filled in order for it to satisfy the octet rule.

Shapes of MoleculesVSEPR

Theory• Valence Shell Electron Pair Repulsion

• System for predicting molecular shape based on the idea that pairs of electrons orient themselves as far apart as possible.

Shapes of MoleculesHow to use VSEPR theory• Total Electron Pairs

– # of Shared and unshared pairs

• Shared Electron Pairs– # of Pairs involved in

covalent bonding• Unshared electron Pairs

– # of Lone pairs of electron• Shape or Geometry

– Linear, bent, trigonal planar, tetrahedral

Examples• HBr

• H2O

• PH3

Shapes of Molecules

What do we do with multiple bonds?

Count the sides of the central atom that have bonds on them

Examples• N2

• HCN

• H2CO

Practice

• Shapes of molecules

THE PASS IT GAME!!

• You will have one paper for each row.• Your job is to do one section and then pass it to

the next person.• There are three sections: Electron dot, molecular

drawing and VSEPR name & angle• Once the last person is done raise your hand and

get a stamp if all is correct.• 1st team will get a prize for each Pass it game!

CCl4

SeO3

BeF2

Polarity of MoleculesElectronegativity

Polar Covalent Bonds

Polar Molecule– Ex. H2O

• Ability to attract electrons• Difference in electronegativity tells us

who wants the electrons more.

• Atoms do not share electrons evenly.• Atoms with greater electronegativity

have a slight negative charge.

• A molecule is polar if the charge is not evenly distributed

Polarity of MoleculesWhat would make

a Non-Polar Covalent Bond?

– Examples• F2

• PH3

• If the 2 atoms have similar electronegativities.

• The atoms involved exert similar pull on the electrons.

Bond Types and Elctronegativity

Electronegativity Difference

Bond Type

< 0.4 Non- polar covalent

Between 0.5 and 1.9 Polar covalent

> 2.0 Ionic

Polarity of Molecules

• Other side of shapes• Draw each molecule in its correct VSEPR

shape.

PropertiesIonic vs. Covalent

Rally Table - Types of chemical bonds

Covalent Compounds

Naming Binary Covalent Compounds

Covalent compoundDefinition

• Non-metal and non-metal• Share Electrons• Nonpolar and polar molecules

Naming Binary Covalent Compounds

Prefixes 1= mono2= di3 = tri4 = tetra5 = penta6 = hexa7 = hepta8 = octa9 = nona10 = deca

Examples:

• Naming water H2O

• Carbon Dioxide

Activity

• Write the names of

• CCl4

• CO• SO2

• NF3

*___________________*___________________*___________________*___________________

Naming Binary Covalent Compounds

PracticeName Formula

What is the formula for the following compounds?

a. Pentachlorine dioxideb. Carbon monoxidec. Tribromine hexasulfide

Practice

• Naming Covalent Compounds worksheet