5.9 Polyatomic Compounds

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Polyatomic Compounds Polyatomic compounds are pure substance that involve combinations of polyatomic ions with metals, hydrogen, and other polyatomic ions. metal hydrogen poly.ion

+ + +

poly.ion poly.ion poly.ion

= = =

poly.cmpd

Polyatomic ions are groups of atoms that tend to stay together and carry an overall charge. When a polyatomic compound is mixed with water the metal separates from the polyatomic ion.

Writing Formulas for Polyatomic Compounds (Use handout: Common Polyatomic Ions and Compounds) • • • •

Write the symbols Find the ionic charges Crisscross the charges (no need for the subscript 1) Reduce to lowest terms ***caution***

Examples: Sodium sulfate

Lead (IV) carbonate

Na+1(SO4)-2

Pb+4(CO3)-2

Na2(SO4)

Pb2(CO3)4 Pb(CO3)2

(reduced)

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Writing Names for Polyatomic Compounds • Name of metal / polyatomic ion / hydrogen • Name of polyatomic ion Typically, it is the positively cation followed by the negatively charged polyatomic anion.

Oxyacids Oxyacids are compounds formed when hydrogen combines whith polyatomic ions that contain oxygen. Examples: Nitric acid Nitrous acid Chloric acid Carbonic acid Sulfuric acid Sulfurous acid Phosphoric acid

HNO3 HNO2 HClO3 H2CO3 H2SO4 H2SO3 H3PO4

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COMMON IONS Symbols and Charges for Monoatomic Ions Fixed Charge Symbol

Name

Symbol

Name

H+ Li+ Na+ K+ Rb+ Cs+ Ag+ Be2+ Mg2+ Ca2+ Sr2+ Ba2+ Ra2+ Zn2+ Al3+

hydrogen ion lithium ion sodium ion potassium ion rubidium ion cesium ion silver ion beryllium ion magnesium ion calcium ion strontium ion barium ion radium ion zinc ion aluminum ion

HFClBrI-

hydride fluoride chloride bromide iodide

O2S2Se2Te2-

oxide sulfide selenide telluride

N3P3As3-

nitride phosphide arsenide

Symbols and Charges for Monoatomic Ions (Variable Charge) Symbol Cu+ Cu2+ Fe2+ Fe3+ Sn2+ Sn4+ Cr2+ Cr3+ Mn2+ Mn3+

Systematic name Common (Stock system) copper(I) mercurous copper(II) iron(II) iron(III) tin(II) tin(IV) chromium(II) chromium(III) manganese(II) manganese(III)

Common name

Systematic name Symbol

(Stock system)

cuprous

Hg22+

mercury(I)

cupric ferrous ferric stannous stannic chromous chromic manganous manganic

Hg2+ Pb2+ Pb4+ Co2+ Co3+ Au+ Au3+

mercury(II) lead(II) lead(IV) cobalt(II) cobalt(III) gold(I) gold(III)

Symbols and Charges for Polyatomic Ions Formula NO3NO2CrO42Cr2O72CNMnO4OHO22NH2CO32SO42SO32C2O42PO43PO33S2O32AsO43SeO42SiO32C4H4O62C2H3O2-

Name Formula Name nitrate ClO4perchlorate nitrite ClO3chlorate chromate ClO2chlorite dichromate ClOhypochlorite cyanide IO4periodate permanganate IO3iodate hydroxide IOhypoiodite peroxide BrO3bromate amide BrOhypobromite carbonate HCO3hydrogen carbonate (bicarbonate) sulfate HSO4hydrogen sulfate (bisulfate) sulfite HSO3hydrogen sulfite (bisulfite) oxalate HC2O4hydrogen oxalate (binoxalate) phosphate HPO42hydrogen phosphate phosphite H2PO4dihydrogen phosphate thiosulfate HShydrogen sulfide arsenate BO33borate selenate B4O72tetraborate silicate SiF62hexafluorosilicate tartrate acetate (an alternate way to write acetate is CH3COO-)

There is one positive polyatomic ion. It is NH4+ and is called the ammonium ion.

name mercuric plumbous plumbic cobaltous cobaltic aurous auric