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 !
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