Ionic BondingIonic Bonding

akaaka Electrovalent bonds

Ionic BondIonic Bond

Chemical bond resulting from Chemical bond resulting from electrostatic attraction between electrostatic attraction between positivepositive and and negativenegative ions. ions.

– Goal: achieve stable octet of electrons Goal: achieve stable octet of electrons (noble gas configuration)(noble gas configuration)

Illustrate byIllustrate by– Orbital notationOrbital notation– Lewis Dot diagramsLewis Dot diagrams

Three Types of BondingThree Types of Bonding

IonicIonic – electrons are transferred.electrons are transferred.

CovalentCovalent– electrons are shared.electrons are shared.

MetallicMetallic– “ “sea of mobile electrons.”sea of mobile electrons.”

Identify Bond Type from FormulaIdentify Bond Type from Formula

Ionic CompoundsIonic Compounds– metal + nonmetalmetal + nonmetal

Covalent CompoundsCovalent Compounds – all nonmetalsall nonmetals

MetallicMetallic– all metalsall metals

Force of AttractionForce of Attraction

                                                                   

Show transfer of VALENCE electrons to achieve octet

A quantum mechanical representation of the electron transfer

But WHICH electrons (i.e. what orbitals) are involved?

Formation ofThe Octets

Na metal Na metal

Metals Metals loselose e e-

ClCl22 (g) (g)

Nonmetals gain e-

Ionic CompoundsIonic Compounds Composed of Composed of positivepositive and and negativenegative ions ions

combined so that compound is combined so that compound is NEUTRALNEUTRAL..

Most ionic compounds are …Most ionic compounds are …crystalline solids.crystalline solids.

Expressed as Expressed as Formula UnitsFormula Units, not , not molecules (which are covalent)!molecules (which are covalent)!– Simplest ratio of atoms (Simplest ratio of atoms (empirical formulaempirical formula))

Structure of Ionic CompoundsStructure of Ionic Compounds

Ions are attracted to each other by strong Ions are attracted to each other by strong electrostatic interactionselectrostatic interactions..

Form a Form a crystal latticecrystal lattice– a regular 3-D pattern or array.a regular 3-D pattern or array.– Ions are held in Ions are held in fixed positionsfixed positions in the solid state. in the solid state.

Unit CellUnit Cell = smallest repetitive unit in lattice = smallest repetitive unit in lattice

Electron is transferred from Na to Cl

Tiger Graphic

Ionic ReactionsIonic Reactions

Strength of Ionic BondStrength of Ionic Bond

Lattice EnergyLattice Energy– Energy Energy releasedreleased

when one mole of when one mole of an ionic crystalline an ionic crystalline compound is compound is formed from formed from gaseous ions.gaseous ions.

Na+(g) + Cl−(g) → NaCl(s)

The experimental lattice energy of NaCl is −787 kJ/mol.

Shown as negative value Exothermic

Trends in Lattice EnergyTrends in Lattice Energy

Lattice Energy* and Interionic Distance

700

750

800

850

900

950

1000

1050

1100

209 257 296

Interionic Distance (pm)

Lat

tice

En

erg

y (k

J/m

ol)

*

* positive values show n

Interionic Distance

Increases

as Lattice Energy

Decreases

LiF

LiCl

LiI

Trends in Lattice EnergyTrends in Lattice EnergyLattice Energy*and Compound Size

0200400600800

10001200

Ionic Compound

Lat

tice

En

erg

y (k

J/m

ol)

*

* positive values show n

State the trend here…

Factors that Affect Lattice EnergyFactors that Affect Lattice Energy

Related to the SIZE of the ions Related to the SIZE of the ions bonded.bonded.– Smaller ions generally have a Smaller ions generally have a moremore

negative (larger) lattice energy.negative (larger) lattice energy.

Affected by the CHARGE on the ion.Affected by the CHARGE on the ion.– Larger charged atoms generally have a Larger charged atoms generally have a

more negative (larger) lattice energymore negative (larger) lattice energy

Oxidation NumberOxidation NumberDetermines how many atoms are needed to form the ionic compound.

Ionic Bond FormationIonic Bond Formation

Release ENERGYRelease ENERGY

NaCl

Na + Cl

Pote

nti

al Energ

y

Decreasing energy

means greater stability!

Properties of Ionic CompoundsProperties of Ionic Compounds

HighHigh melting points melting points LowLow vapor pressures vapor pressures SolidsSolids do do notnot conduct electricity conduct electricity Melts (liquids) Melts (liquids) dodo conduct electricity conduct electricity SolutionsSolutions (aq)(aq) conduct electricity conduct electricity

– electrolytes: electrolytes: substances whose water solution substances whose water solution conducts an electric current.conducts an electric current.

Tend to be Tend to be hardhard and and brittlebrittle HighHigh solubilitysolubility in water. in water.

Linus PaulingLinus Pauling

1954 Nobel Prize Chemistry1954 Nobel Prize Chemistry

First to show that chemical First to show that chemical bonds could show bonds could show degreesdegrees of of both a covalent and ionic both a covalent and ionic nature.nature.

Led to the development of Led to the development of electronegativity valueselectronegativity values. .

Electronegativity DifferenceElectronegativity Difference

1.7

Electronegavitity DifferenceElectronegavitity Difference Bonding between atoms is a Bonding between atoms is a continuum continuum

from ionic to covalent.from ionic to covalent.

The The largerlarger the difference in the difference in electronegativity between two bonded electronegativity between two bonded elements, the more ionic in character the elements, the more ionic in character the bond bond has.has.

Which has more ionic character?Which has more ionic character?– CaO or KF or LiHCaO or KF or LiH

Crystal Coordination NumberCrystal Coordination Number

The The coordination numbercoordination number of an atom in a of an atom in a molecule or a crystal is the integer molecule or a crystal is the integer number of its nearest neighbors.number of its nearest neighbors.

Salt Crystals - CubicSalt Crystals - Cubic