11

Mr. Shields Regents Chemistry U09 L02

22

Ionic compounds form Crystalline structuresof alternating atoms forming geometric patterns

Multiple repeating units Are the basis of crystal formation

33

The Formula unit of an ionic compounds can goOn an indefinite no. of times, for example NaxClx

Many naturalGems such as Rubies, saphiresAnd emeraldshave uniquecrystalline patternsBased on Al2O3

When we write NaCl We are using what is knownAs an Empirical formula i.e. the formula unit.

44

Emeralds

Sapphires & Rubies

55

Properties of IONIC CompoundsProperties of IONIC CompoundsPROPERTY IONIC COMPOUND

Simplest Component Formula UnitStructure CrystallineHardness HardWorkability Shatters if workedElectrical Conductivity Good Conductor ONLY if

molten or in solutionMelting Point High (NaCl – 801 deg C)Boiling Point High (NaCl – 1413 deg C)Ease of Phase Change Difficult – Low VP / High MP &

BP’s / High Hf

Solubility in Water Soluble – Covers range from very soluble to insolubleNaCl = 37.5g/100g water

66

Conductivity of Ionic compounds

When ionic compoundsAre dissolved or meltedThe crystal lattice breaksDown.

In the crystal lattice ions are not free to move.

When dissolved or molten these ions can move.- If a voltage is applied cations will flow to one electrode and anions will flow to the other

- this movement of ions means there is a flow flow of electricity

77

Lewis dot structuresLewis dot structures

• For For CATIONS (+) CATIONS (+) we draw the ion with only the we draw the ion with only the symbol & charge & sometimes with Brackets symbol & charge & sometimes with Brackets NaNa++ ( or [Na] ( or [Na]+ + ) Fe) Fe3+3+

• For For ANIONSANIONS we draw the ion with its valence electrons enclosed we draw the ion with its valence electrons enclosed in in bracketsbrackets and the charge indicated outside the brackets and the charge indicated outside the brackets

[ O ] 2-

• What does the lewis dot structure of an What does the lewis dot structure of an ionic compoundionic compound look like?look like?

88

Lewis dot structuresLewis dot structuresWriting Lewis dot structures for Ionic compounds follow theWriting Lewis dot structures for Ionic compounds follow theSame rules with some additionsSame rules with some additions

The The CationCation (+) is written (+) is written firstfirst

The AnionThe Anion (-) is written (-) is written secondsecond

Number of ions are specified as a prefix in front of Number of ions are specified as a prefix in front of brackets brackets OROR the ion is written twice. the ion is written twice.

99

Lewis dot structure examplesLewis dot structure examples

[ Br ] -K+

-[ Cl ]3[Al]3+

[ Br ] -

[ Br ] -Ca2+

[ O ] 2-2[Na]+[ O ] 2-[Na]+

[Na]+

Ca2+ 2 [ Br ] - or

KBr

AlCl3

CaBr2

Na2O or

1010

PolyatomicsPolyatomicsWe’ve discussed the formation ionic compounds betweentwo elements, one being + and the other –

for ex. NaCl, CaF2, K2O, Al2O3 or AlCl3

These are called binary compounds (two elements)

However ionic compoundscan also form betweenMultiple elements

for ex. CuSO4 , K3PO4, K2CrO4 or NH4NO3

So what’s the difference between these2 types of ionic compounds?

Very pretty!

1111

PolyatomicsPolyatomicsThese multi atom ionic compounds are formedWith ions known as POLYATOMICS

Polyatomic Ions can have either + or – charge

They are groups of atoms joined together bycovalent bonds that behave as charged ions.Therefore they can form Ionic compounds

- example: Na+ + NO3- NaNO3

(We’ll discuss covalent bonds in the next unit)

1212

These are theCommon Polyatomic Anions and Cations

You need tolearn their names &formulasAnd to recognizeThem as polyatomics!

Dimercury (I) Hg22+

Hydronium ion H3O+

Look at table E in your reference table

To cations add:

1313

PolyatomicsPolyatomicsNotice there are many more anions(-) than cations (+).

Some polyatomics ALSO contain a Metal and nonmetal

example: Chromate CrO42-, or Permangenate MnO4

-

And remember Polyatomics form ionic compounds withmetals just like any other binary compound

2K+ + CrO4 2- K2CrO4 (Potassium Chromate)

1414

What are the names of the following polyatomics?

1. OH-

2. NH4+

3. ClO-

4. H3O+

5. CN-

6. NO3-

What are the formulas of these polyatomics?

1. Nitrite2. Sulfate

3. Perchlorate4. Hydronium

5. Phosphate6. Carbonate

1515

Polyatomic Lewis Dot Polyatomic Lewis Dot StructuresStructures

Writing Lewis dot structures for Ionic compounds Writing Lewis dot structures for Ionic compounds containing containing Polyatomic IonsPolyatomic Ions (such as the nitrate ion) (such as the nitrate ion)in Cu(NOin Cu(NO33))22 is a little more complicated is a little more complicated

This additional complexity arises because This additional complexity arises because polyatomicpolyatomicions containions contain covalentcovalent bonds bonds

We’ll talk about these later after we discuss We’ll talk about these later after we discuss covalentcovalentBonds.Bonds.