HONORS CHEMISTRY

Oct 30, 2013

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.

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 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 (refer to back of P. table)– 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.• Transition metals are not as predictable, but +2

and +3 are common.– 3 transition metals with fixed charge (Ag+1, Zn+2 Cd+2)

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

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?

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

Draw Lewis Dot Structure!!!

Metal Non-Metal

What holds Ionic bonds together?

• Electrostatic Attraction • + and - charge

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

• Mg and C

Practice

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

• Make formulas from the following ions:

Mg2+, OH- Fe2+, PO43- 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 FormulasChemical Formulas

• Remember • Combine ions to obtain electrical neutrality

Ionic_Formula.exeIonic_Formula.exe

STOP

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

More examples:

NaCl

CaS

AlF3

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 (criss-cross method).

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 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.

Examples

• Fe3P2

• Cu2S

• NiO

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

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

Examples

• Copper (II) nitride• Vanadium (II) oxide• Zinc chloride

• 3 Special Transition Metals (do not require Roman numerals: fixed charge):– Zn

– Cd

– Ag

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

• Refer to “Naming Ionic Compounds Practice Worksheet”

• Make Flash Cards: Polyatomic Ions

Start 11/5/12

Brain Teaser (11/5/12)• Write the formula and draw the Lewis Dot

structure: Potassium and Phosphorus

• Name or Write the formula of the following compounds:– SrS

– Cu2S

– Iron (II) oxide– Magnesium cyanide

Agenda (11/5)

• Brain Teaser• Collect Progress Report• Grade Practice Ionic Bonding Quiz and WS• Questions?• Ionic Review Questions• Ionic Bonding Quiz• Notes: Covalent Bond• Homework

– Study Ionic Compounds Worksheet

• 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

Round Table – Covalent Bonding

• SiH4

• NH41+

• H2Se

• HCl

• HF

• *SO42-

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

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 Molecules

VSEPR 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 Molecules

How 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 Molecules

Electronegativity

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 Molecules

What 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