IV

Lesson Essential Questions:› Why do atoms form chemical bonds?› How is the type of chemical bond

determined?

Vocabulary: chemical bond, ionic bonding, covalent bonding, nonpolar-covalent bonding, polar, polar-covalent bonding

Chemical Bond

› attractive force between atoms or ions that binds them together as a unit

› bonds form in order to… decrease potential energy (PE) increase stability

ION

PolyatomicIon

MonatomicIon

1 atom 2 or more atoms

NONO33--NaNa++

IONIC COVALENTBond Formation

Type of Structure

Solubility in Water

Electrical Conductivity

OtherProperties

e- are transferred from metal to nonmetal

high

yes (solution or liquid)

yes

e- are shared between two nonmetals

low

no

usually not

MeltingPoint

crystal lattice true molecules

Physical State solid Solid, liquid, or gas

odorous

“electron sea”

METALLICBond Formation

Type of Structure

Solubility in Water

Electrical Conductivity

OtherProperties

MeltingPoint

Physical State

e- are delocalized among metal atoms

very high

yes (any form)

no

malleable, ductile, lustrous

solid

Ionic Bonding - Crystal Lattice

RETURN

Covalent Bonding - True Molecules

RETURN

Diatomic Molecule

Metallic Bonding - “Electron Sea”

RETURN

Most bonds are a blend of ionic and covalent characteristics.

Difference in electronegativity determines bond type.

Electronegativity› Attraction an atom has for a shared pair of

electrons.› higher e-neg atom -

› lower e-neg atom +

Electronegativity Trend› Increases up and to the right.

Nonpolar Covalent Bond› e- are shared equally› symmetrical e- density› usually identical atoms

+ -

Polar Covalent Bond› e- are shared unequally› asymmetrical e- density› results in partial charges (dipole)

Nonpolar

Polar

Ionic

View Bonding Animations.

Examples:

Cl2

HCl

NaCl

3.0-3.0=0.0Nonpolar

3.0-2.1=0.9Polar

3.0-0.9=2.1Ionic

What type of bonding would be expected between the following atoms?› Li and Cl› Ca and Ga› I and Cl› K and Na

Lesson Essential Questions:› How is a molecular compound formed?› What are some of the characteristics of a

covalent bond?

Vocabulary: molecule, chemical formula, molecular formula, bond energy, electron-dot, Lewis structure, structural formula, single bond, multiple bonds, resonance

Covalent bond – bond that is created by the sharing of electrons

Molecule – neutral group of atoms held together by covalent bonds

Molecular compound – chemical compound made of molecules

CHEMICAL FORMULA

MolecularFormula

FormulaUnit

IONIC COVALENT

COCO22NaClNaCl

Potential Energy› based on position of an object› low PE =

high stability

no interaction

attraction vs. repulsion

increased attraction

Potential Energy Diagram

balanced attraction & repulsion

increased repulsion

attraction vs. repulsion

Potential Energy Diagram

Bond Energy

Bond Energy› Energy required to break a bond

Bond Length

Bond Energy› Short bond = high bond energy

Electron Dot Diagrams1. Pick the central atom2. Count the valence electrons (they are

what electron dot diagrams show)3. Place electrons around the atom

Octet Rule› Most atoms form bonds in order to obtain 8

valence e-

› Full energy level stability ~ Noble Gases

Ne

+ -

+

Nonpolar Covalent - no charges

Polar Covalent - partial charges

On page 186 in your text book do practice problems #1-4

1. Draw the Lewis structure of ammonia, NH3

2. Draw the Lewis structure for hydrogen sulfide, H2S

3. Draw the Lewis structure for silane, SiH4

4. Draw the Lewis structure for phosphorus trifluoride, PF3

Some elements can share more than one electron pair.› Double bond (two pairs of electrons are

shared)› Triple bond (three pairs of electrons are

shared)

Draw Lewis structures for each of the following molecules:› O2

› CO2

› N3

› N2

Occurs when more than one valid Lewis structure can be written for a particular molecule (due to position of double bond)

•These are resonance structures of benzene.

•The actual structure is an average (or hybrid)

of these structures.

Neither structure is correct, it is actually a hybrid

of the two. To show it, draw all varieties

possible, and join them with a double-headed

arrow.

Note the different location of the

double bond

Resonance in

a carbonate ion

(CO32-):

Resonance in

an acetate ion

(C2H3O21-):

Prefix System (binary compounds)

1. Less e-neg atom comes first.

2. Add prefixes to indicate # of atoms. Omit mono- prefix on first element.

3. Change the ending of the second element to -ide.

PREFIXmono-di-tri-tetra-penta-hexa-hepta-octa-nona-deca-

NUMBER12345678910

CCl4

N2O

SF6

carbon tetrachloride

dinitrogen monoxide

sulfur hexafluoride

arsenic trichloride

dinitrogen pentoxide

tetraphosphorus decoxide

AsCl3

N2O5

P4O10

Lesson Essential Questions:› How is an ionic bond formed?› What are some of the characteristics of an

ionic bond?

Vocabulary: ionic compound, formula unit, lattice energy, polyatomic ion

Ionic compound – composed of positive and negative ions that are combined so that the charges are equal.

CHEMICAL FORMULA

MolecularFormula

FormulaUnit

IONIC COVALENT

COCO22NaClNaCl

Electron dot notation is used to note changes.

Form to create an atmosphere of stability

Covalent – show sharing of e-

Ionic – show transfer of e-

Ions minimize potential energy in crystals by forming a crystal lattice.

Distance between all ions represent a balance of attraction between oppositely charged particles and repulsion between like charged particles

Lattice Energy› Energy released when one mole

of an ionic crystalline compound is formed from gaseous ions

Ionic High melting

temperature High boiling point Hard Brittle, because

slight shift of crystal can cause it to break

Conduct electricity when dissolved in water

Covalent Low melting

temperature Low boiling point Do not conduct

electricity Not as brittle

Ionic Formulas Write each ion, cation first. Don’t show

charges in the final formula. Overall charge must equal zero.

› If charges cancel, just write symbols.› If not, use subscripts to balance charges.

Use parentheses to show more than one polyatomic ion.

Stock System - Roman numerals indicate the ion’s charge.

Ionic Names

Write the names of both ions, cation first.

Change ending of monatomic ions to -ide.

Polyatomic ions have special names.

Stock System - Use Roman numerals to show the ion’s charge if more than one is possible. Overall charge must equal zero.

Consider the following:› Does it contain a polyatomic ion?

-ide, 2 elements no -ate, -ite, 3+ elements yes

› Does it contain a Roman numeral? Check the table for metals not in Groups 1 or

2.

› No prefixes!

Common Ion Charges

1+

2+ 3+ NA 3- 2- 1-

0

potassium chloride

magnesium nitrate

copper(II) chloride

K+ Cl

Mg2+ NO3

Cu2+ Cl

KCl

Mg(NO3)2

CuCl2

NaBr

Na2CO3

FeCl3

sodium bromide

sodium carbonate

iron(III) chloride

Lesson Essential Questions:› How is a metallic bond formed?› What are some of the characteristics of a

metallic bond?

Vocabulary: metallic bond, alloy

Metal ions held together by attraction to free floating electrons. (Sea of electrons)

Good conductors of electricity – Why?

Malleable Ductile Bond strength – related to enthalpy of

vaporization› The more energy required to vaporize, the

stronger the bond.› See table on page 196.

A mixture of two or more substances, one of which must be a metal.

Common alloys include steel, 14K gold, 18K gold, cast iron, sterling silver, and bronze.

Within different alloys, there can be different types of mixtures – ex. Steel

Where do we find alloys?

Use the 3 circle Venn diagram to compare and contrast ionic, metallic, and covalent bonding.

Metallic

Venn Diagram on Chemical Bonding Name______________________________________

Ionic Covalent

Lesson Essential Questions:› How is the VSEPR Theory useful?› What are the different forces present in

bonding?

Vocabulary:VSEPR theory, hybridization, dipole,

hydrogen bonding, London dispersion forces

Valence Shell Electron Pair Repulsion Theory

Electron pairs orient themselves in order to minimize repulsive forces.

Types of e- Pairs› Bonding pairs - form bonds› Lone pairs - nonbonding e-

Lone pairs repel

more strongly than

bonding pairs!!!

Lone pairs reduce the bond angle between atoms.

Bond Angle

Draw the Lewis Diagram. Tally up e- pairs on central atom.

› double/triple bonds = ONE pair

Shape is determined by the # of bonding pairs and lone pairs.

Know the 8 common shapes

& their bond angles!

2 total2 bond0 lone

LINEAR

180°BeH2

3 total3 bond0 lone

TRIGONAL PLANAR

120°

BF3

3 total2 bond1 lone

BENT

<120°

SO2

4 total4 bond0 lone

TETRAHEDRAL

109.5°

CH4

4 total3 bond1 lone

TRIGONAL PYRAMIDAL

107°

NH3

4 total2 bond2 lone

BENT

104.5°

H2O

5 total5 bond0 lone

TRIGONAL

BIPYRAMIDAL120°/90°PCl5

6 total6 bond0 lone

OCTAHEDRAL

90°

SF6

PF3

4 total

3 bond

1 loneTRIGONAL

PYRAMIDAL

107°

CO2

2 total

2 bond

0 loneLINEAR

180°

Identify the molecular geometry for the following molecules:› HI

› CBr4

› CH2Cl2

Intermolecular forces = forces between molecules.

› The boiling point of a liquid is a good measure of the intermolecular forces between its molecules: the higher the boiling point, the stronger the forces between the molecules.

Types of intermolecular forces› Dipole-dipole forces› Hydrogen bonding› London dispersion forces

Dipole – created by equal but opposite charges that are separated by a short distance.

A dipole is represented by an arrow with its head pointing toward the negative pole and a crossed tail at the positive pole. The dipole created by a hydrogen chloride molecule is indicated as follows:

Dipole-dipole forces are the forces of attraction between polar molecules.

H Cl

The negative region in one polar molecule attracts the positive region in adjacent molecules. So the molecules all attract each other from opposite sides.

Dipole-dipole forces act at short range, only between nearby molecules.

Hydrogen bonding = intermolecular force in which a hydrogen atom that is bonded to a highly electronegative atom is attracted to an unshared pair of electrons in a nearby molecule.

London Dispersion Forces = intermolecular attractions resulting from the constant motion of electrons and the creation of instantaneous dipoles.

http://itl.chem.ufl.edu/2045/matter/FG11_005.GIF

Modern Chemistry Textbook www.nclark.net http://mrsj.exofire.net/chem/ http://cottonchemistry.bizland.com/

chem/chemnotes1.htm http://www.unit5.org/chemistry/