Ch.3 - Chemical ReactionsSee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds
Jules Bruno

Polyatomic ions are tightly bound groups composed of multiple elements that possess an overall charge. The positively charged ions are called cations, while the negatively charged ions are called anions. 

The charts below show some of the most common polyatomic ions grouped by their respective charges. Unfortunately when it comes to learn them all you will have to seat down and memorize. 

The one major +1 charge polyatomic ion is the ammonium ion. 

NH4-Ion-AmmoniumAmmonium Ion

The +2 charge cation is the mercury (I) ion, which is composed of two mercury ions that are bonded together to form a dimer.  

Mercury-I-Ion-Hg2+-cationMercury (I) Ion

There are many - 1 charge anions and these are the most commonly recognized. 

Acetate-CH3CO3-C2H3O2-CN-OH-NO3-NO2-HCO3-HSO3-HSO4-H2PO4-SCN-OCN-MnO4-H2PO3-1 Charge Polyatomic Anions

Polyatomic ions containing halogens are referred to as oxyhalogens or halogen oxyanions. 

Perchlorate-chlorate-chlorite-hypochlorite-HClO-HClO2-HClO3-HClO4Halogen Oxyanions

The most common – 2 charge polyatomic ions are: 

C2O4-CO3-CrO4-Cr2O7-HPO4-O2-SO3-SO4-SiO3-S2O3-2 Charge Polyatomic Anions

The most common – 3 charge polyatomic ions are: 

PO4-PO3-AsO4-Phosphate-phosphite-arsenite-3 Charge Polyatomic Anions

Memorizing these polyatomic ions will be essential later on when dealing with naming binary molecular compounds, ionic compounds, and oxyacids. In addition our review on the various charges will be further discussed when calculating oxidation states and oxidation numbers, 


Jules Bruno

Jules felt a void in his life after his English degree from Duke, so he started tutoring in 2007 and got a B.S. in Chemistry from FIU. He’s exceptionally skilled at making concepts dead simple and helping students in covalent bonds of knowledge.


Additional Problems
The ion MnO4– is called permanganate, which would you expect the formula of the manganate ion to be?
The chemical name of the ion IO3- is: a) periodate b) hypoiodite c) iodate d) iodide e) iodite
Which of the following does not have a charge of –1? (A) nitrate (B) hydroxide (C) ammonium (D) chloride (E) acetate
The chemical name of the ion IO3– is: a. periodate b. hypoiodite c. iodate d. iodide e. iodite
Polyatomic ions are compounds made up of different elements, usually only NONMETALS, and possess a CHARGE. 
Which of the following has a charge of –1? (A) ammonium (B) carbonate (C) phosphate (D) sulfate (E) acetate
Bearing in mind the relationship between sulfate and sulfite or nitrate and nitrite, what is the formula of phosphite? (A) PO43- (B) HPO43- (C) PO42- (D) PO33- (E) PO32-
The correct formula for bromite is: A. BrO2- B. BrO- C. BrO3- D. BrO5- E. BrO4-
The ion NO2– is named A) nitrogen dioxide ion. B) nitrogen(II) oxide ion. C) nitrite ion. D) nitrate ion. 
Polyatomic ions are compounds made up of different elements that possess a CHARGE.  
Recall that metals possessing multiple charges are referred to as Type II Metals. Below we have the formal or IUPAC name of some of the most common Type II metals as well as their older latin derived name. 
Breaking News: At 11 am this morning NASA announced that they have evidence liquid water still flows on Mars. Water can stay liquid at such low temperature because of the high concentration of salt dissolved in the water, and some scientists believe perchlorate ions play a major role.   Write a formula for the perchlorate ion.
Give the chemical formula for chlorite ion.
Give the chemical formula for chloride ion.
Give the chemical formula for chlorate ion.
Give the chemical formula for perchlorate ion.
Give the chemical formula for hypochlorite ion.
What information is conveyed by the endings -ide, -ate, and -ite in the name of an anion?
Elements in the same group of the periodic table often form oxyanions with the same general formula. The anions are also named in a similar fashion. Based on these observations, suggest a chemical formula or name, as appropriate, for each of the following ions.hydrogen tellurate ion.
The correct name for the ClO3- ion isa) perchlorate ionb) hypochlorite ionc) chlorite iond) chlorate ione) chlorine trioxide ion
Dimensional AnalysisHow many milligrams in 125.0 gram   ____________________The boiling point of H2 is -253°C, what is the boiling point in Kelvin. ________________Oil has a density of 0.916 g/ml. What is the mass of 225 mL of the oil? ________________What is the formula and charge of the phosphate ion? ___________________ 
What is the name of the following polyatomic ion, BrO 3 – ?a) Bromateb) Bromidec) Perbromated) Hypobromite Based on the previous question, the compound HBrO 3 is correctly named as:a) Hydrobromic acidb) Bromous acidc) Bromic acidd) Perbromic acid
What is the charge of the sulfide ion?  ________________
The prefix “bi” is added to anion names to indicate an extra positive hydrogen, as for example, in bicarbonate compared to carbonate. Which of the following anions would be known as biphosphate?(A) HP-(B) (PO4)22-(C) HPO32-(D) HPO42-(E) HPO43-
In K2O2, the oxygen is called aa. dioxideb. oxidec. peroxided. peroxitee. superoxide
Elements in the same family often form oxyanions of the same general formula. The anions are named in a similar fashion. What are the names of the oxyanions of selenium and tellurium:SeO42–, SeO32–, TeO42–, TeO32–?
Give the chemical formula for (a) chlorite ion
Give the chemical formula for (b) chloride ion
Give the chemical formula for (c) chlorate ion
Give the chemical formula for (d) perchlorate ion
Give the chemical formula for (e) hypochlorite ion
Selenium, an element required nutritionally in trace quantities, forms compounds analogous to sulfur. Name the following ions: (a) SeO42–
The preferred name for HSO4- is hydrogen sulfate. What is the common name for this ion?A) bisulfateB) disulfateC) bisulfideD) disulfide
The naming of polyatomic anions, while seemingly random, actually does have some rules. Two in particular concern the use of the prefix “bi” , which is used to indicate an extra positive hydrogen, and the difference between the suffices "ite" and "ate," which is based on number of oxygen atoms ("ite" means one less than "ate"). These are exemplified by the differences between carbonate and bicarbonate and sulfite and sulfate, respectively! Given this, what is the formula of biphosphite?(A) HP-(B) (PO4)22-(C) HPO32-(D) HPO42-(E) PO33-
Write the ions present in solution of {Cu(C2H3O2)2}
Elements in the same group of the periodic table often form oxyanions with the same general formula. The anions are also named in a similar fashion. Based on these observations, suggest a chemical formula or name, as appropriate, for each of the following ions.arsenate ion
What is the formula for the carbonate ion? 
What is the formula for the chlorate ion?
What is the charge of cobalt in Co(NO3)3?a. -3b. -1c. +1d. +2e. +3
What is the name for SO42-? The ____________ ion.