Bonding: General Concepts

Bonding: General ConceptsBonding: General Concepts

Chapter 8Chapter 8

Types of Chemical BondsTypes of Chemical BondsBond Energy is _____________________ Bond Energy is _____________________

_________________________________._________________________________. Compounds always strive to be at the lowest energy Compounds always strive to be at the lowest energy

orientation possible. They will bond or not bond orientation possible. They will bond or not bond depending on whether or not it is favorable from an depending on whether or not it is favorable from an energy perspective.energy perspective.

A higher value for bond energy indicates a stronger A higher value for bond energy indicates a stronger bond. bond.

Ionic BondingIonic BondingAn ionic bond forms when electrons are An ionic bond forms when electrons are

_________ between atoms. When this _________ between atoms. When this happens both atoms become _____; one happens both atoms become _____; one positive (____ of e-), the other negative positive (____ of e-), the other negative (_____ of e-).(_____ of e-).

• This type of bonding occurs between a _________ This type of bonding occurs between a _________ and a _____________.and a _____________.• Elements bonded by an ionic bond form Elements bonded by an ionic bond form ionic compoundsionic compounds..

Coulomb’s LawCoulomb’s Law

Describes _____________ between two Describes _____________ between two particles.particles.

_______ values indicate attraction, while _______ values indicate attraction, while _______ values indicate repulsive forces._______ values indicate repulsive forces.

Ion pairs have lower energy (more favorable) Ion pairs have lower energy (more favorable) when they are ______________________.when they are ______________________.

E =

Bond LengthBond Length

Bond length is the distance between two ions Bond length is the distance between two ions that maximizes the favorable attractions and that maximizes the favorable attractions and minimizes the amount of repulsive forces.minimizes the amount of repulsive forces.

Favorable attractive forces:Favorable attractive forces:

Unfavorable attractive forces (repulsive forces):Unfavorable attractive forces (repulsive forces):

Covalent and Polar Covalent BondsCovalent and Polar Covalent Bonds

A Covalent Bond occurs when two nuclei A Covalent Bond occurs when two nuclei _________ electrons._________ electrons.

Occurs between two _____________ atoms.Occurs between two _____________ atoms.

Polar Covalent bonds occur when two Polar Covalent bonds occur when two nuclei _________________________.nuclei _________________________.

The dipoles (+ and – centers) that are formed give the The dipoles (+ and – centers) that are formed give the covalent bond more ionic character than normal.covalent bond more ionic character than normal.

Lower case delta (Lower case delta () is used to indicate partial charge.) is used to indicate partial charge.

ElectronegativityElectronegativity

Follows the trend for electron affinity Follows the trend for electron affinity (synonymous), which means that it (synonymous), which means that it increases as we move ________ a group increases as we move ________ a group and _________ a period on the periodic and _________ a period on the periodic table.table.

Electronegativity is __________________ Electronegativity is __________________ _________________________________._________________________________.

Electronegativity affects bondsElectronegativity affects bonds If bonded atoms have a large difference in electronegativity If bonded atoms have a large difference in electronegativity

(2.0 or greater), they are considered to have an _________ (2.0 or greater), they are considered to have an _________ bond because _____________________________________.bond because _____________________________________.

If bonded atoms have a moderate difference in electronegativity If bonded atoms have a moderate difference in electronegativity (0.5-1.6), they are considered to have a _______(0.5-1.6), they are considered to have a _______--__________ __________ bond because _____________________________________.bond because _____________________________________.

If bonded atoms have a negligible difference in electronegativity If bonded atoms have a negligible difference in electronegativity (below 0.5), they will be considered to have a ___________ (below 0.5), they will be considered to have a ___________ bond because ______________________________________.bond because ______________________________________.

If bonded atoms have a difference in electronegativity between If bonded atoms have a difference in electronegativity between 1.6 and 2.0, their identities have to be considered. If a metal is 1.6 and 2.0, their identities have to be considered. If a metal is involved, it will be deemed ionic. If 2 non-metals are bonded, it involved, it will be deemed ionic. If 2 non-metals are bonded, it will be considered polar-covalent.will be considered polar-covalent.

Bond Polarity and Dipole MomentsBond Polarity and Dipole Moments

Dipoles are formed in _________ bonds.Dipoles are formed in _________ bonds. If the dipoles (a form of force) are aligned to If the dipoles (a form of force) are aligned to

point in exactly equal and opposite point in exactly equal and opposite directions, they will _________________.directions, they will _________________.

This makes the molecule non-polar.This makes the molecule non-polar. The bond remains polar.The bond remains polar. Molecules must be symmetrical for the cancellation to Molecules must be symmetrical for the cancellation to

occur. Shapes that cancel are (draw them):occur. Shapes that cancel are (draw them):

1. 2. 3.

AssignmentAssignmentArrange the bonds in each of the following Arrange the bonds in each of the following

set in order of increasing polarityset in order of increasing polarityC-F, O-F, Be-FC-F, O-F, Be-FO-Cl, S-Br, C-PO-Cl, S-Br, C-PC-S, B-F, N-OC-S, B-F, N-O

Using only the periodic table as a guide, Using only the periodic table as a guide, select select

A) the most electronegative element in group 6AA) the most electronegative element in group 6AB) The least electronegative element out of Al, Si, PB) The least electronegative element out of Al, Si, PC) The element in the group K, C, Zn, F that is most C) The element in the group K, C, Zn, F that is most

likely to form an ionic compound with Ba.likely to form an ionic compound with Ba.

Give three ions that are isoelectronic with Give three ions that are isoelectronic with argon. Place these ions in order of argon. Place these ions in order of increasing size.increasing size.

What two requirements must be satisfied for What two requirements must be satisfied for a molecule to be polar?a molecule to be polar?

Rank the following bonds in order of Rank the following bonds in order of increasing ionic character:increasing ionic character:

N-O, Ca-O, C-F, Br-Br, K-FN-O, Ca-O, C-F, Br-Br, K-F

Section 5:Section 5: Formation of Binary Ionic CompoundsFormation of Binary Ionic Compounds

Lattice energy: the energy required to Lattice energy: the energy required to combine elements to form an ionic combine elements to form an ionic compound. (amount released when bond compound. (amount released when bond forms)forms)

Lattice energy is negative. Lattice energy is negative. Elements must start as a gasElements must start as a gas The more exothermic (negative), the more likely the The more exothermic (negative), the more likely the

substance is to form spontaneously.substance is to form spontaneously.

Steps involved in forming ionic Steps involved in forming ionic bonds from elements.bonds from elements.

Vaporization of elements. (endo)Vaporization of elements. (endo)

LiLi(s)(s) Li Li(g)(g) F F2(g) 2(g) 2F 2F(g)(g)

Ionization of elements. (exo)Ionization of elements. (exo)

LiLi(g)(g) Li Li++ (g)(g) + e + e-- FF(g)(g) + e + e-- F F--(g)(g)

Formation of solid by combination of ions. Formation of solid by combination of ions. (very exo)(very exo)

LiLi++(g)(g) + F + F--(g)(g) LiF LiF(s)(s)

Energy DiagramEnergy Diagram

Partial Ionic Character of Covalent Partial Ionic Character of Covalent BondsBonds

100% xcharacterionicYdipoleXcalculated

YdipoleXmeasured

Any Compound That Conducts Electricity

When MeltedIs IONIC

Models of Chemical BondsModels of Chemical Bonds

Models do not equal reality…they are Models do not equal reality…they are merely something to help us visualize a merely something to help us visualize a concept near the truth.concept near the truth.

Models are often wrong because they Models are often wrong because they over-simplify.over-simplify.

Covalent Bond EnergyCovalent Bond Energy

Single bond = one pair shared electronsSingle bond = one pair shared electronsDouble bond = two pair shared electronsDouble bond = two pair shared electronsTriple bond = three pair shared electronsTriple bond = three pair shared electrons

As more pairs of electrons are shared, the bond length As more pairs of electrons are shared, the bond length shortens. (more orbitals have to overlap to allow the shortens. (more orbitals have to overlap to allow the sharing to happen)sharing to happen)

Single bonds usually contain the least amount of energy, Single bonds usually contain the least amount of energy, while triple bonds usually contain the most…as bond while triple bonds usually contain the most…as bond length shortens, bond energy increases.length shortens, bond energy increases.

Page 374 Tables 8.4 and 8.5

Covalent Bond Energy CalculationCovalent Bond Energy Calculation

HHbondbond = sum energies required to break old = sum energies required to break old

bonds (positive signs) plus the sum of bonds (positive signs) plus the sum of energies required to form new bonds energies required to form new bonds (negative signs)(negative signs)

HHbondbond = = bonds broken – bonds broken – bonds formedbonds formed

Use values in the tables on pg 374.Use values in the tables on pg 374.

Covalent Bond Energy CalculationCovalent Bond Energy Calculation

Using the bond energies listed in Table 8.4, Using the bond energies listed in Table 8.4, calculate the calculate the H for the reaction of methane H for the reaction of methane with chlorine and fluorine to give Freon-12 with chlorine and fluorine to give Freon-12 (CF(CF22ClCl22).).

CHCH4(g)4(g) + 2Cl + 2Cl2(g)2(g) + 2F + 2F2(g)2(g) CF CF22ClCl2(g)2(g) + 2HF + 2HF(g)(g) + 2HCl + 2HCl(g)(g)

The VSEPR ModelThe VSEPR Model

Valence Shell Electron Pair RepulsionValence Shell Electron Pair RepulsionA model of molecular structure based on A model of molecular structure based on

the idea that ideal structures minimizes the idea that ideal structures minimizes electron pair repulsions.electron pair repulsions.

Draw and evaluate Lewis StructuresDraw and evaluate Lewis Structures

Molecular Geometry ModelsMolecular Geometry Models We look at the molecular geometry of a single We look at the molecular geometry of a single

atom, not of an entire molecule.atom, not of an entire molecule. Constituent groups are the things bonded to the Constituent groups are the things bonded to the

atom under scrutiny.atom under scrutiny. Dashed lines represent a bond behind the plane Dashed lines represent a bond behind the plane

of the paper; wedged lines represent a bond of the paper; wedged lines represent a bond coming toward you (in front of the paper plane)coming toward you (in front of the paper plane)

Bent

2 Constituents1 Lone Pair

Bond Angle: <120o

Trigonal Planar


Bond Angle: 120o

Linear

1-2 Constituents0 Lone Pair

Bond Angle: 180o

Planar GeometryPlanar Geometry

Tetrahedral

4Constituents0 Lone Pair

Bond Angle: 109.5o

Trigonal Pyramidal


Bond Angle: 107.3o

Bent


Bond Angle: 104.5o

Tetrahedral and DerivativesTetrahedral and Derivatives

Trigonal Bipyramidal


Bond Angle: 90o, 120o

See-Saw


Bond Angle: <90o, <,120o, <180o

T-Shaped


Bond Angle: <90o, <180o

Linear


Bond Angle: 180o

Trigonal Bipyramidal and DerivativesTrigonal Bipyramidal and Derivatives

Square Planar


Bond Angle: 90o

Square Pyramidal


Bond Angle: <90o

Octahedral


Bond Angle: 90o

Octahedral and DerivativesOctahedral and Derivatives

Hybridization of OrbitalsHybridization of Orbitalsaka Localized Electron Modelaka Localized Electron Model

Natural orbitals overlap to form hybridized orbitals Natural orbitals overlap to form hybridized orbitals during bonding.during bonding.

2 types of bonding2 types of bonding Sigma (Sigma ( bonds = take equatorial positions, can be hybridized. bonds = take equatorial positions, can be hybridized. Pi (Pi () bonds = take axial positions, exist in non-hybridized ) bonds = take axial positions, exist in non-hybridized

orbitalsorbitals

Possibilities for hybridization:Possibilities for hybridization:spsp3 3 spsp22 spspdspdsp33 dd22spsp33

How to become HybridHow to become Hybrid

Orbitals in which bonding electrons exist will Orbitals in which bonding electrons exist will become degenerate (equal energy).become degenerate (equal energy).

2p ___2p ___ ______ ______ __ __ __ __ __ __ __ __

spsp33

2s ___2s ___

By becoming equal energy, they also acquire By becoming equal energy, they also acquire same shape.same shape.

spsp3 3 HybridizationHybridization

Atoms with 4 constituent groupsAtoms with 4 constituent groupsTetrahedral shapesTetrahedral shapes

spsp22 hybridization hybridization

3 constituent groups3 constituent groupsTrigonal planarTrigonal planar

spsp22 continues continues

One p orbital remains un-hybridized. This One p orbital remains un-hybridized. This orbital has the ability to house lone pairs orbital has the ability to house lone pairs as well as form a double bond (pi bond!)as well as form a double bond (pi bond!)

sp hybridizationsp hybridization2 constituents2 constituentsLinearLinear

Now 2 extra p remain un-hybridized. Now 2 extra p remain un-hybridized. 2 double bonds, or 1 triple bond can form.2 double bonds, or 1 triple bond can form.

dspdsp33 and d and d22spsp33 hybridization hybridization

dspdsp33 allows for 5 constituent groups allows for 5 constituent groups trigonal bipyramidaltrigonal bipyramidal

dd22spsp33 allows for 6 constituent groups allows for 6 constituent groupsoctahedraloctahedral

Molecular Orbital TheoryMolecular Orbital Theory

This is an alternative to the idea of This is an alternative to the idea of hybridized orbitals.hybridized orbitals.

Essentially, when two atoms come Essentially, when two atoms come together their orbitals merge and form two together their orbitals merge and form two completely new orbitals.completely new orbitals.

Bonding orbital (low energy, electrons fill first)Bonding orbital (low energy, electrons fill first)Anti-bonding orbital (high energy, electrons fill last)Anti-bonding orbital (high energy, electrons fill last)

Homonuclear Diatomic Homonuclear Diatomic Molecular OrbitalsMolecular Orbitals

The number of The number of molecular orbitals should molecular orbitals should equal the number of equal the number of orbitals you start with. orbitals you start with.

In the case of p orbitals, In the case of p orbitals, one is a sigma orbital, one is a sigma orbital, and two are pi orbitals. and two are pi orbitals.

Ones with stars are anti-Ones with stars are anti-bonding orbitals.bonding orbitals.

Determining Bond OrderDetermining Bond Order

You can use molecular orbitals to You can use molecular orbitals to determine bond order to a much more determine bond order to a much more specific degree than you can with a Lewis specific degree than you can with a Lewis Dot Diagram.Dot Diagram.

Delocalized ElectronsDelocalized Electrons

Alternating double and single bonds Alternating double and single bonds around a molecule can lead to available around a molecule can lead to available unused p orbitals that create a cloud of unused p orbitals that create a cloud of available space for electrons to sit in.available space for electrons to sit in.

This is very stable.This is very stable.

Complex Ions andComplex Ions andCoordination CompoundsCoordination Compounds

Highly colored compoundsHighly colored compoundsParamagnetic (unpaired electrons)Paramagnetic (unpaired electrons)Made of a Transition Metal and LigandsMade of a Transition Metal and Ligands

How do they do that?How do they do that?

Transition metals have two sets of valence Transition metals have two sets of valence electrons.electrons.Primary valence electrons affect oxidation Primary valence electrons affect oxidation

state (charge in ions) and allow for trading of state (charge in ions) and allow for trading of electrons (ionic bonds).electrons (ionic bonds).

Secondary valence electrons affect Secondary valence electrons affect coordination number (number of ligands) and coordination number (number of ligands) and allow for ligands to share electrons with the allow for ligands to share electrons with the transition metal.transition metal.

LigandsLigands

Ligands are molecules or ions that have a Ligands are molecules or ions that have a lone pair of electrons available to lone pair of electrons available to coordinate with the transition metal. coordinate with the transition metal.

Rule of Thumb: The coordination number Rule of Thumb: The coordination number of a metal can generally be assumed as of a metal can generally be assumed as twice its charge. twice its charge.

Ex: CoEx: Co+3+3 can have a coordination number of 6. can have a coordination number of 6.

Naming Complex IonsNaming Complex Ions

Name cations firstName cations firstChange ending of ligands to –oChange ending of ligands to –oUse prefixes to tell how many.Use prefixes to tell how many.List oxidation state of metal using Roman List oxidation state of metal using Roman

NumeralsNumeralsList ligands in alphabetical orderList ligands in alphabetical order If complex ion is an anion, end metal If complex ion is an anion, end metal

name with –ate.name with –ate.

ExamplesExamples

[Al(OH)[Al(OH)44]]--

[Co(NH[Co(NH33))44 ] ]2+2+ Amminetetraaquachromium(II) sulfate Potassium hexacyanoferrate(III)

IsomersIsomers

A set of compounds with the same A set of compounds with the same chemical formula that exhibit decidedly chemical formula that exhibit decidedly different properties.different properties.

Structural Isomer = the same atoms are present in each Structural Isomer = the same atoms are present in each molecule, but they are bonded to different things.molecule, but they are bonded to different things.

Stereoisomer = bonds are between same atoms, but Stereoisomer = bonds are between same atoms, but have a different spatial relationship with each other.have a different spatial relationship with each other.

Concept MapConcept Map

ISOMERS

STEREOISOMERS

OpticalCoordination

IsomersLinkage Isomers

Geometric

STRUCTURAL These are the ones we care about.

Geometric IsomersGeometric Isomers

Come in two forms: cis and transCome in two forms: cis and transcis- prefix represents that similar cis- prefix represents that similar

constituent groups are on the SAME side.constituent groups are on the SAME side. trans- prefix represents that similar trans- prefix represents that similar

constituent groups are on OPPOSITE constituent groups are on OPPOSITE sides.sides.

More Complicated cis-, trans-More Complicated cis-, trans-

Optical IsomersOptical Isomers

Two forms of the molecule have different Two forms of the molecule have different effects on plane polarized light. (one form effects on plane polarized light. (one form creates destructive interference)creates destructive interference)

These isomers are These isomers are non-super non-super imposable mirror imagesimposable mirror images. .

Each isomer is referred to as an Each isomer is referred to as an ENANTIOMER. ENANTIOMER.

The chemical formula is said to have The chemical formula is said to have CHIRALITY.CHIRALITY.

Bonding: General Concepts

Documents

bond polarity

stronger bond

bond lengthbond length

bondsif bonded atoms

ionic character

lower energy

energy perspective

large difference