CHAPTER 5.1

IONIC COMPOUNDS

IONIC COMPOUNDS

• Charged ions with neutral cpd.• Water soluble• Metal with non metal• Brittle• Electric conductor• Tightly bound repeating patterns in crystals

• Cation: + charged ion• Anion: - charged ion

Types of Ionic CompoundsI. Binary Ionic Compounds• only contains 2 elements

(can have more than one ion of each element)

- Bi – Latin for “2”

Ex: NaCl sodium chloride - charges cancel each other - compound is neutral

- do not write charges of ions in formula

- 1:1 ratio of each element

Binary Ionic Compoundsex: CaFl2 calcium flouride

(1:2 ratio)

AlCl3 aluminum chloride (1:3 ratio)

K2S potassium sulfide (2:1 ratio)

Naming Binary Ionic Compounds

Rules 1. Write name of metal

( + cation)

2. Write name of non metal (- anion)

3. Change non metal name to end in “ide” (number of each element does not change

name)

Name the following binary compounds:

Mg2O3

magnesium oxide

KCl potassium chloride

Na2S sodium sulfide

LiI lithium iodide

TiBr titanium bromide

Writing FormulasRules

1. If more than one ion of an element is present, the subscript tells how many

2. Write subscript below and to the right of element (sub-below)

3. Write the formula unit (simplest ratio of elements)

Ex: FORMULA UNIT REPEATING PATTERNCaF2 Ca2F4 Ca3F6

NaCl Na2Cl2 Na6Cl6

Ga2S3 Ga4S6 Ga8S12

Write the formula units for the following:

Rb2F2

RbF

Mg3Cl9

MgCl3

Al6O18

AlO3

C12H24O12

CH2O

H4S2O8

H2SO4

Writing Binary Ionic FormulasRules

1. Write the symbol for the metal then the non-metal

2. Determine the oxidation number of each element (use periodic table)

oxidation number: charge on ion (superscript)- tells number of electrons atom gains

or loses

Oxidation NumbersMetals:

- always have + charge (lose negative electrons)

- charge equals group # on periodic tbl. (remove 1 in front of group 13)

Oxidation NumbersNon metals:

- always have – charge (gain negative electrons)- charge equals 8 minus group # (remove 1 in front of groups 15, 16, 17, 18)

3. Rewrite formula so compound is neutral (positive and negative charges must be equal)

ex: Mg2+ Br –

Are the charges equal? In order for the compound to be neutral we must have equal positive and negative charges.

CRISS-CROSS RULE 1. take number of metal’s superscript (number above element)

2. move this number to bottom right of non-metal symbol (now a subscript, loses charge)

3. do the same for the non-metal

Criss Cross Rule

Ex: Mg Br

Mg 2+ Br -

Mg1 Br

2

Final Formula (do not write charges on subscripts)Mg Br

2charges are equal, compound is neutralMg has 2+ charges x one atom = 2+ chargesBr has 1- charge x two atoms = 2- charges

II. Polyatomic Compounds compound that contains more than two elements

• Polyatomic Ion: Ion that has two or more different elements in a grouped unit which carries a charge

a. whole ion is charged, not last element listed

b. treated same as single element’s (monoatomic) ion

ex: ammonium cyanideNH

4+CN-

polyatomic polyatomicion ion

c. can contain:

1. one (+) metal bonded to (–) polyatomic ion

Na+OH-

metal nonmetal

2. (+) polyatomic ion bonded to one (-) non metal ion

NH4

+I-

polyatomic nonmetal ion

3. (+) polyatomic ion bonded to a (-) polyatomic ion

NH4

+NO3

-

polyatomic polyatomic

Naming Polyatomic Compounds

Rules

1. name + ion first, followed by name of – polyatomic ion

2. do not change ending of – polyatomic ion

ex: CaCO3

calcium carbonate

Name the following polyatomic compounds:

(use reference sheet)LiNO2lithium nitrate

MgSO4magnesium sulfate

CaPO4calcium phosphate

NaOHsodium hydroxide

* H3OCl hydronium chloride

* Remember to change non metal’s name to “ide”

NaCNsodium cyanide

AlSO3 aluminum sulfite

KNO3potassium nitrate

MgCr2O7magnesium dichromate

* NH4I ammonium iodide

Writing Polyatomic Formulas

Rules1. Use criss-cross method

2. Put parenthesis around polyatomic ion

3. Criss-cross superscript to bottom right of parenthesis around polyatomic ion

ammonium nitride NH4

+ N3-

(NH4) 3 N1

hydronium phosphide

H3O + P2-

(H3O)2P

Practice Problems

III. Transition Element Compounds (groups 3-12)

a. form + ions like metals

b. can have more than one type of + ion (have more than 1 oxidation number)

c. named by using name of element followed by oxidation number as Roman numeral in

parenthesis

ex: Cu(I)Cl copper I chloride Cu(II)Clcopper II chloride

IV. Hydratesionic compound that contains H2O molecules weakly bound in its crystals - when hydrates lose their water, the end compound has different properties than the original hydrate

ex: popcorn kernel popped corn yellow, hardwhite, soft

cobalt chloride cobalt chloride (anhydrous) (hydrate)

cement gel cement hardened

Hygroscopic substances:Ionic compounds that easily become hydrates (absorb

H2O)The thorny devil features hygroscopic grooves between the spines of their skin to capture water in their desert habitat.

Deliquescent substances:Substance that absorbs so much water it becomes liquid

salts

Dessicants:Absorb water vapor and keeps surrounding substance dry

silica gel packs inside electronics

Anhydrous compound:Hydrate with all water removed

anhydrous sodium sulfate

Naming Hydrates

Rules1. Write the name of the compound

2. Write the prefix of the number of water molecules

3. Add the word “hydrate” to the prefix

ex: Ba(NO3)2 . 4 H2O barium nitrite tetrahydrate

Prefixes for Naming Compounds

Number Prefix1 Mono-2 Di-3 Tri-4 Tetra-5 Penta-6 Hexa-7 Hepta-8 Octa-9 Nona-

10 Deca-

Name the following hydrates:

CaSO4 . 3 H2O

NaSO4 . 4 H2O

NiNo3 . 6 H2O

FeO2 . 7 H2O

NaOH . 9 H2O

LiPO4 . 10 H2O

AlSO3 . 5 H2O

MgCr2O7 . H2O

KCl . 2 H2O

BaOH . 8 H2O

Writing Hydrate FormulasRules1. Write the formula for the compound (must be

neutralized)

2. Place a dot after formula

3. Write the number of water molecules

ex: copper sulfate dihydrate CuSO4 . 2 H2O

sodium carbonate pentahydrate Na2CO3 . 5 H2O

Write the formulas for the following hydrates:

Beryllium sulfite pentahydrateCesium chloride trihydrateCopper (I) phosphate decahydrateBarium oxide octahydrateCalcium hydroxide dihydrateScandium (II) bromide trihydrateSodium carbonate nonahydratePotassium sulfide heptahydrateRadium flouride hexahydrateAmmonium cyanide monohydrate

Study for the test !