Chapter 11 Chemical Bonds: The Formation of Compounds from Atoms Objectives: Describe the trends in the periodic table Describe the trends in the periodic

Chapter 11Chapter 11Chemical Bonds:Chemical Bonds:The Formation of Compounds from The Formation of Compounds from

AtomsAtomsObjectives:Objectives:

Describe the trends in the periodic tableDescribe the trends in the periodic tableKnow how to draw Lewis Structures of atomsKnow how to draw Lewis Structures of atomsUnderstand and predict the formation of ionic bondsUnderstand and predict the formation of ionic bondsUnderstand and predict covalent bondsUnderstand and predict covalent bondsDescribe electronegativityDescribe electronegativityKnow how to draw complex lewis structures of compoundsKnow how to draw complex lewis structures of compoundsUnderstand the formation of compounds containing polyatomic Understand the formation of compounds containing polyatomic ionsionsDescribe molecular shape, including the VSEPR modelDescribe molecular shape, including the VSEPR model

Periodic Trends in Atomic Periodic Trends in Atomic PropertiesProperties

Periodic table designed to show Periodic table designed to show trendstrends Use trends to predict properties and Use trends to predict properties and

reactions between elementsreactions between elements Trends include:Trends include:

Metals, nonmetals, metalloidsMetals, nonmetals, metalloids Atomic radiusAtomic radius Ionization energyIonization energy ElectronegativityElectronegativity

Metals, Nonmetals and Metals, Nonmetals and MetalloidsMetalloids

Metals:Metals: Lustrous, malleable, good conductors of Lustrous, malleable, good conductors of

heat and electricityheat and electricity Left-hand side of tableLeft-hand side of table Most elements are metalsMost elements are metals Tend to lose electrons and form positive Tend to lose electrons and form positive

ionsions


Nonmetals:Nonmetals: Nonlustrous, brittle, poor conductorsNonlustrous, brittle, poor conductors (Hydrogen displays nonmetallic (Hydrogen displays nonmetallic

properties under normal conditions but properties under normal conditions but is UNIQUE element)is UNIQUE element)


MetalloidsMetalloids Found along border between metals and Found along border between metals and

nonmetalsnonmetals

Metal + NonmetalMetal + Nonmetal Usually electrons are transferred from Usually electrons are transferred from

metal to nonmetal…metal to nonmetal…

Atomic RadiusAtomic Radius

Increases down each groupIncreases down each group

Decreases from left to right across a Decreases from left to right across a periodperiod Increase in positive charge = stronger Increase in positive charge = stronger

pull on electrons = gradual decrease in pull on electrons = gradual decrease in atomic radiusatomic radius

Atomic RadiusAtomic Radius

Ionization EnergyIonization Energy

The energy required to remove an The energy required to remove an electron from the atomelectron from the atom


Ionization energy in Group A Ionization energy in Group A elements elements

Ionization energy Ionization energy Nonmetals – tend to gain electrons Nonmetals – tend to gain electrons

(rather than give them up)(rather than give them up)


Lewis StructuresLewis Structures

Diagram that shows Diagram that shows valence valence electronselectrons Dots = number of s and p electrons Dots = number of s and p electrons Paired dots = Paired dots =

Simple way of showing electronsSimple way of showing electrons


When drawing:When drawing: ““3, 6, 9” = 3, 6, 9” =

Just like orbital filling diagram…Just like orbital filling diagram… Examples: draw Lewis Structures of Examples: draw Lewis Structures of

B, N, F, NeB, N, F, Ne


NN

BB

NeNe

FF

The Ionic BondThe Ionic Bond Ionic bond: Ionic bond:

Attraction between electrostatic charges Attraction between electrostatic charges

is a is a

The Ionic BondThe Ionic Bond

The Ionic BondThe Ionic Bond NOT A MOLECULENOT A MOLECULE

Bond not just Bond not just between between

The Ionic BondThe Ionic Bond

Typically metal + nonmetalTypically metal + nonmetal

Predicting Formulas of Ionic Predicting Formulas of Ionic CompoundsCompounds

In almost all stable chemical In almost all stable chemical compounds of representative compounds of representative elements, each atom attains a noble elements, each atom attains a noble gas electron configuration. This gas electron configuration. This concept forms the basis for our concept forms the basis for our understanding of chemical bonding.understanding of chemical bonding.


How many electrons must be gained How many electrons must be gained or lost to achieve noble gas or lost to achieve noble gas configuration?configuration?


Elements in a family usually form Elements in a family usually form compounds with the same atomic compounds with the same atomic ratiosratios


The formula for sodium oxide is The formula for sodium oxide is Predict the formula for Predict the formula for

Sodium sulfide Sodium sulfide Sodium [Ne]3sSodium [Ne]3s11 must must Sulfur [Ne]3sSulfur [Ne]3s223p3p44 must must So…formula must So…formula must


Rubidium OxideRubidium Oxide Rubidium [Kr]5sRubidium [Kr]5s11 must must Oxygen [He]2sOxygen [He]2s222p2p44 So…formula must be So…formula must be This makes sense b/c rubidium is in This makes sense b/c rubidium is in

same family as sodiumsame family as sodium

The Covalent BondThe Covalent Bond A pair of electrons A pair of electrons Most common type of bondMost common type of bond Electron orbital expands to include Electron orbital expands to include

both nucleiboth nuclei

The Covalent BondThe Covalent Bond


Atoms may share more than one pair of Atoms may share more than one pair of electronselectrons Double bond – Double bond – Triple bond – Triple bond – Multiple bonds are Multiple bonds are

Covalent bonding between identical atoms Covalent bonding between identical atoms

means electrons are means electrons are Covalent bonding between different atoms Covalent bonding between different atoms

leads to leads to

ElectronegativityElectronegativity

The attractive force that an atom of an The attractive force that an atom of an element has for shared electronselement has for shared electrons

Atoms have different Atoms have different electronegativitieselectronegativities Electrons will spend more time near atom Electrons will spend more time near atom

with stronger (larger) electronegativitywith stronger (larger) electronegativity So…one atom assumes a So…one atom assumes a The other assumes a The other assumes a


Electronegativity trends and periodic Electronegativity trends and periodic tabletable See table 11.5 page 237See table 11.5 page 237 Generally increases from left to rightGenerally increases from left to right Decreases down a group Decreases down a group Highest is fluorine (4.0)Highest is fluorine (4.0) Lowest is francium (0.7)Lowest is francium (0.7)


ElectronegativityElectronegativity Polarity is determined by difference Polarity is determined by difference

in electronegativityin electronegativity Nonpolar covalentNonpolar covalent

Polar covalentPolar covalent

Ionic compoundIonic compound



If the electronegativity difference is If the electronegativity difference is greater than 1.7-1.9 then the bond greater than 1.7-1.9 then the bond will be more ionic than covalentwill be more ionic than covalent

Above 2.0 = Above 2.0 = Below 1.5 = Below 1.5 = See Continuum on page 239See Continuum on page 239


Polar bonds form between two atomsPolar bonds form between two atoms Molecules can also be polar or nonpolarMolecules can also be polar or nonpolar

DipoleDipole

PolarPolar

NonpolarNonpolar

Lewis Structures of Lewis Structures of CompoundsCompounds

Convenient way of showing ionic or Convenient way of showing ionic or covalent bondscovalent bonds

Usually the single atom in a formula Usually the single atom in a formula is the central atomis the central atom

The Ionic BondThe Ionic Bond LEWIS STRUCTURES of ionic bondsLEWIS STRUCTURES of ionic bonds

The Covalent BondThe Covalent Bond LEWIS STRUCTURES of covalent LEWIS STRUCTURES of covalent

bondsbonds Use dashes instead of dots…Use dashes instead of dots…



1)1) Obtain the total number of valence Obtain the total number of valence electronselectrons

1)1) Add the valance electrons of all atomsAdd the valance electrons of all atoms

2)2) Ionic – add one electron for each Ionic – add one electron for each negative charge and subtract one negative charge and subtract one electron for each positive chargeelectron for each positive charge


2)2) Write the skeletal arrangement of Write the skeletal arrangement of the atoms and connect with a single the atoms and connect with a single covalent bondcovalent bond

3)3) Subtract two electrons for each Subtract two electrons for each single bond single bond

1)1) This gives you the net number of This gives you the net number of electrons available for completing the electrons available for completing the structurestructure


4)4) Distribute pairs of electrons around Distribute pairs of electrons around each atom to give each atom a each atom to give each atom a noble gas structurenoble gas structure

5)5) If there are not enough electrons If there are not enough electrons then try to form double and triple then try to form double and triple bonds bonds

Lewis Structures of Lewis Structures of Compounds Compounds

Write the Lewis Structure for methane Write the Lewis Structure for methane CHCH44

1)1) Total number of valence electrons is eightTotal number of valence electrons is eight2)2) Draw skeletal structureDraw skeletal structure

1)1) Dashes equal two electrons being sharedDashes equal two electrons being shared

3)3) Subtract the eight electrons shown as Subtract the eight electrons shown as dashesdashes

4)4) Check that all atoms have a noble gas Check that all atoms have a noble gas structurestructure


Methane, CHMethane, CH44


Carbon Dioxide, COCarbon Dioxide, CO22

Total valence electrons = 16Total valence electrons = 16

Not Enough! Must try double bonds…

Complex Lewis StructuresComplex Lewis Structures

Some molecules and polyatomic ions Some molecules and polyatomic ions have strange behaviors…have strange behaviors… No single Lewis structure is consistentNo single Lewis structure is consistent If multiple structures are possible the If multiple structures are possible the

molecule shows molecule shows resonanceresonance Resonance structures – show all possibilitiesResonance structures – show all possibilities

Complex Lewis StructuresComplex Lewis Structures Carbonate ion, COCarbonate ion, CO33

2-2-

Carbon only has 6 electrons – try double bonds – more than one location…..form resonant structures…

Compounds ContainingCompounds ContainingPolyatomic IonsPolyatomic Ions

Polyatomic ion: stable group of atoms Polyatomic ion: stable group of atoms that has a positive or negative chargethat has a positive or negative charge Behaves as a single unit in many Behaves as a single unit in many

chemical reactionschemical reactions Sodium carbonate (NaSodium carbonate (Na22COCO33))

Carbonate ion (coCarbonate ion (co33) has covalent bonds) has covalent bonds Sodium atoms are ionically bonded to Sodium atoms are ionically bonded to

carbonate ioncarbonate ion

Compounds ContainingCompounds ContainingPolyatomic IonsPolyatomic Ions

Easier to dissociate ionic bond than Easier to dissociate ionic bond than break covalent bondbreak covalent bond More in chapters 6 and 7More in chapters 6 and 7

Molecular ShapeMolecular Shape Three-dimensional shape of molecule Three-dimensional shape of molecule

importantimportant Explains Explains

Helpful to know how to predict the Helpful to know how to predict the geometric shape of molecules…geometric shape of molecules… Linear?Linear? V-shaped?V-shaped? Trigonal planar?Trigonal planar? Tetrahedral?Tetrahedral?

The VSEPR ModelThe VSEPR Model

Valence Shell Electron Pair Repulsion Valence Shell Electron Pair Repulsion ModelModel Make predictions about shape Make predictions about shape Electron pairs will Electron pairs will


Linear StructureLinear Structure 180180oo apart apart

The VSEPR ModelThe VSEPR Model Trigonal Trigonal

PlanarPlanar 120120oo apart apart

The VSEPR ModelThe VSEPR Model Tetrahedral Tetrahedral

structurestructure 109.5109.500 apart apart When drawing:When drawing:

Wedged line to show Wedged line to show atom protruding from atom protruding from page; dashed line to page; dashed line to show atom receding show atom receding from pagefrom page


Pyramidal shapePyramidal shape Four pairs of Four pairs of

electrons on central electrons on central atom BUT only three atom BUT only three shared…shared…

Electrons are Electrons are tetrahedral but tetrahedral but actual shape is more actual shape is more of a pyramidof a pyramid


Electron pairs determine shape BUT Electron pairs determine shape BUT name for shape is determined by name for shape is determined by position of atomsposition of atoms

The VSEPR ModelThe VSEPR Model V-shaped or bentV-shaped or bent

Four electron pairs Four electron pairs but only two sharedbut only two shared

Electron arrangement Electron arrangement is is

But, molecule is But, molecule is WaterWater Helps explain some Helps explain some

propertiesproperties


Predict the shape for .Predict the shape for . Draw the Lewis StructureDraw the Lewis Structure Count the electron pairs and determine Count the electron pairs and determine

the arrangement that will minimize the arrangement that will minimize repulsionsrepulsions

Determine the positions of the atoms Determine the positions of the atoms and name the structureand name the structure

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Chapter 11 Chemical Bonds: The Formation of Compounds from Atoms Objectives: Describe the trends in the periodic table Describe the trends in the periodic