Chapter 22Chapter 22Compounds Between Metals and Compounds Between Metals and

Non-Metals – the Ionic BondNon-Metals – the Ionic Bond

Called SaltsCalled Salts

Near the boundary Near the boundary between metals and between metals and non-metalsnon-metals

semiconductorssemiconductors

Conduction and Conduction and valence bands do not valence bands do not overlapoverlap

Band GapBand Gap

valenceband

conductionband

band gap

E= h times frequency; E= h times frequency; c= wavelength times frequencyc= wavelength times frequency

Red longer wavelength means lower frequency, lower energy.

RedRed photons are emitted photons are emitted from a warm LED; from a warm LED; orangeorange photons are photons are

emitted when the LED is very cold. emitted when the LED is very cold. What happened?What happened?

A.A. The band gap shrinks when The band gap shrinks when the semiconductor gets cold.the semiconductor gets cold.

B.B. No “red” electrons get kicked No “red” electrons get kicked upstairs to fall back down.upstairs to fall back down.

C.C. The band gap increases when The band gap increases when the semiconductor gets cold.the semiconductor gets cold.

Did you read Did you read chapter 22 before coming to chapter 22 before coming to

class? Or do you have a class? Or do you have a Halloween costume?Halloween costume?

a)a) YesYes

b)b) NoNo

Which element Which element will react with water in a way will react with water in a way

most similar to Na?most similar to Na?a)a) OO

b)b) ClCl

c)c) LiLi

d)d) HgHg

Which of the Which of the following has the highest following has the highest

ionization energyionization energya)a) Na (Z=11)Na (Z=11)

b)b) Al (Z=13)Al (Z=13)

c)c) Cl (Z=17)Cl (Z=17)

d)d) Ne (Z=10)Ne (Z=10)

Ionization EnergiesIonization Energies Nobel gasses have largest ionization energies. Nobel gasses have largest ionization energies. Alkali metals have the least.Alkali metals have the least.

Compare and Contrast:Compare and Contrast:Ionic Compounds vs MetalsIonic Compounds vs Metals

Network Solids Network Solids High melting T’sHigh melting T’s Brittle solidsBrittle solids Don’t conduct heat and Don’t conduct heat and

electricity in solidelectricity in solid Often colorless and usually Often colorless and usually

transparent in big chunks transparent in big chunks (White when powdered) (White when powdered)

Network SolidsNetwork Solids High melting T’sHigh melting T’s Malleable Malleable Good conductors of heat and Good conductors of heat and

electricity in solidelectricity in solid OpaqueOpaque

Why???Many closely spaced energy levelswith mobile electronsWHY?

Compare and Contrast:Compare and Contrast:Metals vs Non-MetalsMetals vs Non-Metals

MetalsMetals Large atomsLarge atoms Few valence electronsFew valence electrons Low ionization Low ionization

energiesenergies

Non-metalsNon-metals Small atomsSmall atoms Many valence electronsMany valence electrons High ionization energiesHigh ionization energies

Why do metals and non-metals react?Principles of reactivity:materials react to lower energy and increase entropy of universe

For a given row

How can energy be lowered?How can energy be lowered?Metals lose valence electronsNon-metals gain valence electrons

Transfer of electron from Nato Cl is downhill energetically

Energy levelsnot drawn to scale.Cl levels muchlower in energy!

What about entropy change?What about entropy change?

2Na + Cl2Na + Cl22 = 2NaCl + lots of heat and light = 2NaCl + lots of heat and light

Heat and light – cause an increase in entropy of the surroundings

Quicktime Video of reaction

Na – speck Cl2 yellow gassand at bottom

What are the products? IONSWhat are the products? IONS

Positively chargedSodium ions(11 protons, 10 electrons)

Negatively chargedChloride ions

35 protons, 36 electrons

Electrons belong to individual ions; they are not shared among ions.

neutral atom

Positive ion

NeutralCl atom

NegativeCl ion

Examples of Ionic CompoundsExamples of Ionic Compounds

Ions: same charges

and similar sizes

NaCl

Ions: similar sizes,

but different charges

Na2O

Ions: different

charges and sizes

Al2O3

Describe the structure of each compound: Do ions of one type cluster together?What type of ion immediately surrounds a given ion?How do the answers to these two questions relate to the electric force law?

What prediction could you make about the arrangement of ions in any ionic compound?

Which structure is the form Which structure is the form adopted by Aladopted by Al22OO33 in nature? in nature?

A.

B.

What factor most likelyWhat factor most likely prohibits this structure? prohibits this structure?A.A. Strong repulsive forces Strong repulsive forces

between negative O ions between negative O ions and between positive Al and between positive Al ionsions

B.B. Not electrically neutralNot electrically neutral

C.C. Low entropy organizationLow entropy organization

Compare & Contrast Compare & Contrast Energy LevelsEnergy Levels

IONIC COMPOUND ENERGY LEVELS

many closely spaced levelsspread out over many nucleifew levels -- spaced very far apart

Metal Energy Levels

Energy Levels ExplainEnergy Levels Explain

Ionic SaltsIonic Salts

Transparent inTransparent in

Visible Region of Visible Region of Spectrum –Spectrum –

But absorb in UVBut absorb in UV(exception: salts containing (exception: salts containing

certain transition metal ionscertain transition metal ions

absorb in visible region.)absorb in visible region.)

MetalsMetals

Opaque – absorb inOpaque – absorb in

IR, Visible and UVIR, Visible and UV

l20newcrystal.swf l20photon.swf

Compare and ContrastCompare and ContrastElectron Locations & MobilitiesElectron Locations & Mobilities

Sea of Electrons – mobile; electron density is spread out over many nuclei, delocalized.

+

+

+

+

+

++

+

+

Electrons – localized on individual nucleus (spherically shapedelectron clouds in most ions)

IONIC COMPOUNDS METALS AND ALLOYS

How does the model explain properties How does the model explain properties of salts (ionic compounds) ?of salts (ionic compounds) ?

High melting and High melting and boiling temperatures?boiling temperatures? Strong attractions Strong attractions

between + and – ions between + and – ions Attractive forces act over Attractive forces act over

fairly large atomic fairly large atomic distancesdistances

Brittleness?Brittleness? Strong repulsions when Strong repulsions when

ions with like charge ions with like charge come together; material come together; material shatters to relieve the shatters to relieve the stress.stress.

ELECTRICAL CONDUCTIVITY: ELECTRICAL CONDUCTIVITY: FFlow of electricity requires charge carriers of electricity requires charge carriers that are that are free to movefree to move..

In solid, ions are fixed rigidly in place. No Current can flow!

Melting frees up ions so that they can move, completing the electricalcircuit.

Dissolving salt in water also frees up ions. Current flows!

Even More PropertiesEven More Properties

Why are some ionic materials colored?Why are some ionic materials colored? Because they contain “transition” metals with Because they contain “transition” metals with

more energy levels for electronsmore energy levels for electrons• Example: RubyExample: Ruby

Absorbs blue photons

Absorbs green photons

Doesn’t absorb red photons: reflects red

What Ions Usually Form? What Ions Usually Form? Using the Periodic Table to make predictions.Using the Periodic Table to make predictions.Valence Electrons of Main Group ElementsValence Electrons of Main Group Elements

Unreactive noble gasesdon’t form ions.

Metals LOSE their valence electrons.

Non-metals GAIN enough valence electrons to become “noble”.

The octet ruleThe octet rule

Atoms will most likely form an ion that has Atoms will most likely form an ion that has the the nnss22nnpp66 configuration of the closest configuration of the closest noble gas atom.noble gas atom. Metals take on this configuration by losing Metals take on this configuration by losing

electronselectrons Non-metals take on this configuration by Non-metals take on this configuration by

gaining electronsgaining electrons

FamiliesFamilies

Chlorine and Fluorine will form the same types of Chlorine and Fluorine will form the same types of compounds since their valence electrons are the compounds since their valence electrons are the same number and same orbital type.same number and same orbital type.

1s

2s2p

3d3p3s

1s

2s2p

3d3p3s

9F 17Cl

When Mg When Mg loses its two loses its two electrons, it has the same valence electrons, it has the same valence

electron configuration aselectron configuration as

A.A.He, 1sHe, 1s22

B.B.Ne, 2sNe, 2s222p2p66

C.C.Ar, 3sAr, 3s223p3p66

D.D.Kr, 4sKr, 4s224p4p66

When Br gains one When Br gains one electron, it has electron, it has the same valence electron configuration asthe same valence electron configuration as

1.1. He, 1sHe, 1s22

2.2. Ne, 2sNe, 2s222p2p66

3.3. Ar, 3sAr, 3s223p3p66

4.4. Kr, 4sKr, 4s224p4p66

Beryllium (Be) will Beryllium (Be) will most likely form an ion most likely form an ion

with what charge?with what charge?

a)a) -1-1

b)b) -2-2

c)c) +1+1

d)d) +2+2

What would the What would the chemical formula for magnesium chemical formula for magnesium fluoride (a salt of Mg and F) be? fluoride (a salt of Mg and F) be?

a)a) MgFMgF

b)b) MgMg22FF

c)c) MgFMgF22

d)d) MgFMgF33

Ionic compounds are Ionic compounds are neutral neutral (no net charge). (no net charge). What are the ionic What are the ionic charges in the following compounds?charges in the following compounds?

NaClNaCl

KBrKBr

MgFMgF22

AlAl22OO33

NaNa+1+1 and Cl and Cl-1-1

KK+1+1 and Br and Br-1-1

MgMg+2+2 and F and F-1-1

AlAl+3+3 and O and O-2-2

Naming convention for saltsNaming convention for salts

The metal comes first with its name The metal comes first with its name unchangedunchanged

The nonmetal comes second, with the The nonmetal comes second, with the suffix “ide” appendedsuffix “ide” appended