Download Ionic Compounds Ions of Representative Elements Rules For

Ionic Compounds
Ions of Representative Elements
 Compound composed of ions
 Formed from metal and nonmetal
 Can use periodic table to predict ion charges
 Exception: Contains NH4+ ion
 Infinite array of alternating ions
 Conducts electricity in molten or
aqueous state; ions are free to move
Na + Cl
Na+ + Cl
NaCl(s)
e
 Metals  Cation (+) = group#
 Nonmetals  Anion (-) = 8 – group#
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Rules For Writing Ionic Formulas
1.Cation given first in formula
2.Subscripts in formula must
produce electrically neutral formula
unit
3.Subscripts must be smallest
whole numbers possible
4.Charges on ions not included in
finished formula unit of substance
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Determining Ionic Formula
Ex. Formula of ionic compound formed
when magnesium reacts with oxygen
 Mg: Metal Group 2A  Mg2+
 O: Nonmetal Group 6A  O2–
 To get electrically neutral formula unit,
need 1:1 ratio of Mg2+ and O2–
 Formula: MgO
 If no subscript, then 1 implied
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Shortcut: Ionic Formula
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Your Turn!
What is the correct formula for the formula unit
composed of potassium and sulfide ions?
“Criss-cross” rule
 Make magnitude of charge on one ion into
subscript for other
K1+ S2–
 When doing this, make sure that subscripts are
reduced to lowest whole number.
K2S
What is the correct formula for the formula unit
composed of lithium and nitride ions?
Ex. What is the formula of ionic compound
formed between aluminum and oxygen
ions?
Al3+ O2–
Al2O3
Li1+ N3–
Li3N
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Cations of Transition Metals
Cations of Post-transition Metals
Center (shorter) region of periodic table
Much less reactive than group 1A and 2A
Number of electrons transferred less clear
Form more than one positive ion
Can form more than one compound with
same non-metal
e.g. Fe and Cl
Fe2+
Fe3+
FeCl2 or FeCl3
 Appear after transition metals and before
metalloids
 Tin (Sn) and Lead (Pb)





 Both have two possible charges
 Bismuth (Bi)
 Only has +3 charge
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Learning Check
Polyatomic Ions
 Ions composed of two or more atoms
linked by molecular bonds
e.g.
SO32SO42-
Ex. What is the formula of the ionic compound
formed between ammonium and phosphate
ions?
 Ammonium = NH4+
Sulfite
Sulfate typo on notes
 Phosphate = PO43–
NH4+ PO43–
 Strontium = Sr2+
 Nitrate = NO32–
Sr2+ NO3–
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Learning Check:
Determine The Formula
Ex. What is the formula of the ionic compound
formed between calcium and carbonate ions?
 Calcium hydroxide
 Ca(OH)2
 Manganese(II) bromide
 MnBr2
 Ammonium phosphate
 (NH4)3PO4
 Magnesium nitride
 Mg3N2
 Calcium = Ca2+
 Carbonate = CO32– charges cancel out
CaCO3
Ex. Between aluminum ion and sulfite ion?
 Aluminum = Al3+
 Sulfite = SO32–
Al3+ SO32-
Sr(NO3)2
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Learning Check
Ca2+ CO32–
(NH4)3PO4
Ex. Between strontium ion and nitrate ion?
What’s the difference between –ite and –ate?
 Compounds with polyatomic ions may
use parentheses.
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Al2(SO3)3
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