covalent bonding sch3u1 general panet hs. sections 8.1, 8.2, 9.3, and 8.4 sections 6.1 16.1, 6.5...

Covalent Covalent BondingBonding

Sch3u1Sch3u1

General Panet HSGeneral Panet HS

Sections 8.1, 8.2, 9.3, and Sections 8.1, 8.2, 9.3, and *8.4**8.4*

Sections 6.1 16.1, 6.5 and Sections 6.1 16.1, 6.5 and *16.3**16.3*

Remember…Remember…

Ionic bonds form Ionic bonds form between…between…

An ionic bond An ionic bond happens when happens when one atom… and one atom… and the other atom…the other atom…

Remember…Remember…

The definition of The definition of ionic bond is…ionic bond is…

The chemical The chemical formula of an formula of an ionic compound ionic compound represents a…represents a…

Covalent BondsCovalent Bonds The four sentences The four sentences

above represent above represent four of the most four of the most essential essential differences between differences between covalent and ionic covalent and ionic compounds.compounds.

These differences These differences are so important are so important that…that…

Essay Question: Test 3-1

• Define ionic bond and covalent bond. Outline and define, in detail, four major differences between ionic compounds and molecular (covalent) compounds.

Molecular CompoundsMolecular Compounds Formed by covalent Formed by covalent

bondsbonds

Ionic compounds are Ionic compounds are generally crystalline generally crystalline solids at room solids at room temperature.temperature.

Molecular compounds Molecular compounds (CO(CO22 and water, for and water, for example, have VERY example, have VERY different properties.)different properties.)

Molecular CompoundsMolecular Compounds

Molecular Molecular compounds are compounds are formed through formed through covalent bonds.covalent bonds.

Covalent bonds are Covalent bonds are created when created when atoms SHARE atoms SHARE electrons, instead electrons, instead of gaining and of gaining and losing them.losing them.

VocabularyVocabulary MoleculeMolecule: group of atoms : group of atoms

joined by covalent bondsjoined by covalent bonds

Diatomic moleculesDiatomic molecules: : molecules consisting of molecules consisting of two atomstwo atoms

Molecular formulaMolecular formula: : shows how many atoms shows how many atoms of each element a of each element a molecule containsmolecule contains

Think About It…Think About It…

Chlorine is a diatomic element, Chlorine is a diatomic element, meaning that it exists in its atomic meaning that it exists in its atomic state as two bonded atoms.state as two bonded atoms.

Draw two chlorine atoms.Draw two chlorine atoms.

Is the bond between these two Is the bond between these two atoms ionic or covalent? How do atoms ionic or covalent? How do you know?you know?

Properties of Molecular Properties of Molecular CompoundsCompounds

Covalent bonds usually occur between…Covalent bonds usually occur between…

Often are gases or liquids at room temperatureOften are gases or liquids at room temperature

Images will show atoms “stuck” to one anotherImages will show atoms “stuck” to one another

Properties of Molecular Properties of Molecular CompoundsCompounds

In general, In general, melting and melting and boiling points of boiling points of molecular molecular compounds are compounds are lower than ionic lower than ionic compoundscompounds

Molecular FormulasMolecular Formulas

Molecular formula of a molecular Molecular formula of a molecular compound shows how many atoms compound shows how many atoms of each element are in ONE of each element are in ONE MOLECULE of the compound.MOLECULE of the compound.

(Contrast this with the chemical (Contrast this with the chemical formula of ionic compounds, formula of ionic compounds, which show only the ratio of which show only the ratio of elements in the compound.)elements in the compound.)

Molecular FormulasMolecular Formulas Example:Example:

IONIC: Calcium chloride – CaClIONIC: Calcium chloride – CaCl22 Means that in the compound there are Means that in the compound there are

two chloride ions for every one calcium two chloride ions for every one calcium ionion

COVALENT: Carbon dioxide – COCOVALENT: Carbon dioxide – CO22 Means that each carbon dioxide molecule Means that each carbon dioxide molecule

consists of one carbon atom bonded to consists of one carbon atom bonded to two oxygen atomstwo oxygen atoms


Molecular compounds Molecular compounds can be significantly can be significantly larger than ionic larger than ionic compounds.compounds.

Benzoic Acid: CBenzoic Acid: C77HH66OO22

2,4-2,4-Dichlorophenoxyacetic Dichlorophenoxyacetic acid: Cacid: C88HH66ClCl22OO33


Formulas not Formulas not always in lowest always in lowest termsterms

Example: Ethane Example: Ethane CC22HH66

Formulas do not Formulas do not give molecule’s give molecule’s structure. (It must structure. (It must be inferred.)be inferred.)

Structure DiagramsStructure Diagrams

Molecular Molecular FormulaFormula

Structural Structural FormulaFormula

Ball-and-stick Ball-and-stick modelmodel

Space Filling Space Filling ModelModel

Perspective Perspective drawingdrawing

Forming Covalent Forming Covalent BondsBonds

Octet RuleOctet Rule

In covalent In covalent bonds, atoms bonds, atoms share electrons share electrons so that they fill so that they fill their valence their valence levelslevels

Usually 8 (but Usually 8 (but only 2 for only 2 for hydrogen)hydrogen)

Single Covalent BondsSingle Covalent Bonds

Atoms held Atoms held together by sharing together by sharing one pair of one pair of electrons are said electrons are said to form a SINGLE to form a SINGLE COVALENT BONDCOVALENT BOND

Each atom donates Each atom donates one electron to the one electron to the bondbond


Cl

ClClCl


Cl

ClClCl

Single Bond

Lone Pairs

Covalent BondsCovalent Bonds

Electrons that do not take part in the Electrons that do not take part in the bond are called “lone pairs” or bond are called “lone pairs” or “unshared pairs”“unshared pairs”

Covalent BondsCovalent Bonds Different elements can form different Different elements can form different

numbers of bondsnumbers of bonds

Group 7A elements need one more electron, Group 7A elements need one more electron, and can form one bondand can form one bond

Group 6A elements need two more electrons Group 6A elements need two more electrons and can form two bondsand can form two bonds

Group 5A – three bondsGroup 5A – three bonds

Group 4A – four bondsGroup 4A – four bonds

There

are

exceptio

ns!

Hydrogen, Hydrogen, too!too!

Working With Covalent Working With Covalent BondsBonds

1.1. Draw the electron dot Draw the electron dot structures.structures.

2.2. Determine arrangement.Determine arrangement.

3.3. Replace shared pairs of Replace shared pairs of electrons with a line. (Leave electrons with a line. (Leave lone pairs.)lone pairs.)

Draw Structural Draw Structural FormulasFormulas

NHNH33

HH22SS

PBrPBr33


HH22OO

CHCH44

OFOF22


SClSCl22

NN22HH44

CClCCl44

CHClCHCl33

CC22HH66

HFHFUsually, the atom that can form MORE bonds will be in the center of

the molecule!

Draw Structural Draw Structural Formulas, Part 2Formulas, Part 2

OBrOBr22

PP22HH44

CICI44

CHBrCHBr33

CC22ClCl66

HClHClUsually, the atom that can form MORE bonds will be in the center of

the molecule!

Double and Double and Triple BondsTriple Bonds

Double Covalent BondsDouble Covalent Bonds

Atoms attain Atoms attain noble gas noble gas configuration configuration by sharing by sharing two pairs of two pairs of electrons electrons (four)(four)

Bond length Bond length is shorteris shorter


Oxygen has 6 valence electronsOxygen has 6 valence electrons

O (Group 6A) can form two bondsO (Group 6A) can form two bonds

O O


OCTET RULE NOT FULFILLED!OCTET RULE NOT FULFILLED!

O O


OCTET RULE FULFILLED!OCTET RULE FULFILLED!

O O

Other molecules with Other molecules with double covalent bonds are…double covalent bonds are… COCO22

Ethene, CEthene, C22HH44

Carbonyl, COHCarbonyl, COH22


When counting number of When counting number of valence electrons, double bonds valence electrons, double bonds count as 4 shared electrons.count as 4 shared electrons.

Hydrogen will not form double Hydrogen will not form double covalent bonds… why?covalent bonds… why?

Triple Covalent BondsTriple Covalent Bonds

Atoms attain noble gas configuration by Atoms attain noble gas configuration by sharing three pairs of electrons (six)sharing three pairs of electrons (six)

Bond length is even shorterBond length is even shorter


Nitrogen has 5 valence electronsNitrogen has 5 valence electrons

N (Group 5A) can form three bondsN (Group 5A) can form three bonds

N N


OCTET RULE NOT FULFILLED!OCTET RULE NOT FULFILLED!

N N


OCTET RULE FULFILLED!OCTET RULE FULFILLED!

N N

Other molecules with triple Other molecules with triple covalent bonds are…covalent bonds are…

Acetylene, CAcetylene, C22HH22

Hydrogen Cyanide, HCNHydrogen Cyanide, HCN

Propyne, CPropyne, C33HH44


When counting number of valence When counting number of valence electrons, triple bonds count as 6 electrons, triple bonds count as 6 shared electrons.shared electrons.

Diatomic Diatomic ElementsElements

Diatomic ElementsDiatomic Elements

Diatomic elements exist in their Diatomic elements exist in their atomic forms as binary molecular atomic forms as binary molecular compounds, since covalent bonds form compounds, since covalent bonds form between the atomsbetween the atoms

i.e. a “molecule” of oxygen gas is Oi.e. a “molecule” of oxygen gas is O22, , not Onot O

Diatomic ElementsDiatomic Elements

FF22

ClCl22

BrBr22

II22

HH22

NN22

OO22

Exceptions To Exceptions To The Octet RuleThe Octet Rule

ExceptionsExceptions Compounds cannot satisfy the Octet Rule for Compounds cannot satisfy the Octet Rule for

all atoms if the total number of valence all atoms if the total number of valence electrons is odd.electrons is odd.

NONO22 – total number of valence electrons is 17 – total number of valence electrons is 17

O ON

More Exceptions…More Exceptions… Nonmetals in the Nonmetals in the

third period and third period and beyond can form beyond can form more than 4 bonds, more than 4 bonds, since they have since they have empty empty dd orbitals orbitals where they can where they can “promote” or “store” “promote” or “store” extra extra s s oror p p electrons.electrons.

Ex.: Phosphorus can Ex.: Phosphorus can form 5 bonds.form 5 bonds.

Naming Binary Naming Binary Molecular Molecular

CompoundsCompounds

Naming Molecular Naming Molecular CompoundsCompounds

CO and COCO and CO22 are very different are very different compoundscompounds

How can we distinguish them in their How can we distinguish them in their names?names?


1.1. Confirm that the compound is Confirm that the compound is molecular, not ionic.molecular, not ionic.

2.2. Name the elements in the order Name the elements in the order listed in the formula.listed in the formula.

3.3. Add prefixes to identify the Add prefixes to identify the numbers of each atom in the numbers of each atom in the compound.compound.

Prefixes UsedPrefixes Used

Mono-Mono- 11

Di-Di- 22

Tri-Tri- 33

Tetra-Tetra- 44

Penta-Penta- 55

Hexa-Hexa- 66

Hepta-Hepta- 77

Octa-Octa- 88

Nona-Nona- 99

Deca-Deca- 1010


4.4. Omit the prefix “mono-” on the Omit the prefix “mono-” on the first element in the name.first element in the name.

5.5. Add “-ide” as a suffix at the end Add “-ide” as a suffix at the end of the second element’s name.of the second element’s name.

ExamplesExamples

NN22OO

Nitrogen oxygenNitrogen oxygen

Dinitrogen monoxygenDinitrogen monoxygen

DINITROGEN MONOXIDEDINITROGEN MONOXIDE

Practice: Write the Practice: Write the Molecular FormulaMolecular Formula

Nitrogen trichlorideNitrogen trichloride

Carbon tetrabromideCarbon tetrabromide

Diphosphorus trisulfideDiphosphorus trisulfide

Practice: Write the NamePractice: Write the Name

ClCl22OO88

PHPH33

NN22OO44

SFSF66

HH22OO

SS22FF1010

PClPCl55

NN22FF66

Polar Bonds and Polar Bonds and MoleculesMolecules

ElectronegativityElectronegativity

A measure of how well A measure of how well an atom attracts an atom attracts electronselectrons

Measured in Measured in “Paulings”“Paulings”

In a molecule, some In a molecule, some atoms more forcefully atoms more forcefully attract electrons than attract electrons than othersothers

ElectronegativityElectronegativity Decreases from top to Decreases from top to

bottombottom

Increases from left to Increases from left to rightright

Polar BondsPolar Bonds

Polar bond – covalent Polar bond – covalent bond in which electrons bond in which electrons are shared UNEQUALLYare shared UNEQUALLY

Difference in Difference in electronegativity values electronegativity values controls whether bond controls whether bond is nonpolar, polar, or is nonpolar, polar, or ionicionic


Differences:Differences:

0.0-0.4 0.0-0.4 nonpolar nonpolar covalentcovalent

0.4-2.0 0.4-2.0 polar polar covalentcovalent

2.0+ 2.0+ ionic ionic


Greek letter Delta Greek letter Delta (δ) represents the (δ) represents the partial charge partial charge acquired by acquired by atoms in a polar atoms in a polar bondbond

HH22OO HFHF COCO22

Intermolecular Intermolecular AttractionsAttractions

Polar molecules Polar molecules attracted to one attracted to one another (called another (called dipole interactions)dipole interactions)

Hydrogen bonds Hydrogen bonds are attractions that are attractions that occur between occur between hydrogen and hydrogen and unshared electrons unshared electrons on another on another moleculemolecule

Test ReviewTest Review

Test ReviewTest Review

Covalent bonds – definitionsCovalent bonds – definitions Molecular vs. ionic compoundsMolecular vs. ionic compounds Writing structural formulasWriting structural formulas Writing molecular formulas Writing molecular formulas

(from name or from structure)(from name or from structure) Writing compound namesWriting compound names Information on Polar Bonds (pg. Information on Polar Bonds (pg.

237-240)237-240)

covalent bonding sch3u1 general panet hs. sections 8.1, 8.2, 9.3, and 8.4 sections 6.1 16.1, 6.5...

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covalent bonding sch3u1 general panet hs. sections 8.1, 8.2, 9.3, and *8.4* sections 6.1 16.1, 6.5...

covalent bonding sch3u1 general panet hs. sections 8.1, 8.2, 9.3, and 8.4 sections 6.1 16.1, 6.5...