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
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