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Compounds containing a metal ion with a variable charge

Most of the transition metals can form two or more cations with different charges. Compounds of these metals with nonmetals are named with the same method as compounds in the first category, except the charge of the metal ion is specified by a Roman numeral in parentheses after the name of the metal. The charge of the metal ion is determined from the formula of the compound and the charge of the anion. For example, consider binary ionic compounds of iron and chlorine. Iron typically exhibits a charge of either 2+ or 3+ (see [link] ), and the two corresponding compound formulas are FeCl 2 and FeCl 3 . The simplest name, “iron chloride,” will, in this case, be ambiguous, as it does not distinguish between these two compounds. In cases like this, the charge of the metal ion is included as a Roman numeral in parentheses immediately following the metal name. These two compounds are then unambiguously named iron(II) chloride and iron(III) chloride, respectively. Other examples are provided in [link] .

Names of Some Transition Metal Ionic Compounds
Transition Metal Ionic Compound Name
FeCl 3 iron(III) chloride
Hg 2 O mercury(I) oxide
HgO mercury(II) oxide
Cu 3 (PO 4 ) 2 copper(II) phosphate

Out-of-date nomenclature used the suffixes – ic and – ous to designate metals with higher and lower charges, respectively: Iron(III) chloride, FeCl 3 , was previously called ferric chloride, and iron(II) chloride, FeCl 2 , was known as ferrous chloride. Though this naming convention has been largely abandoned by the scientific community, it remains in use by some segments of industry. For example, you may see the words stannous fluoride on a tube of toothpaste. This represents the formula SnF 2 , which is more properly named tin(II) fluoride. The other fluoride of tin is SnF 4 , which was previously called stannic fluoride but is now named tin(IV) fluoride.

Naming ionic compounds

Name the following ionic compounds, which contain a metal that can have more than one ionic charge:

(a) Fe 2 S 3

(b) CuSe

(c) GaN

(d) CrCl 3

(e) Ti 2 (SO 4 ) 3


The anions in these compounds have a fixed negative charge (S 2− , Se 2− , N 3− , Cl , and SO 4 2− ), and the compounds must be neutral. Because the total number of positive charges in each compound must equal the total number of negative charges, the positive ions must be Fe 3+ , Cu 2+ , Ga 3+ , Cr 3+ , and Ti 3+ . These charges are used in the names of the metal ions:

(a) iron(III) sulfide

(b) copper(II) selenide

(c) gallium(III) nitride

(d) chromium(III) chloride

(e) titanium(III) sulfate

Check your learning

Write the formulas of the following ionic compounds:

(a) chromium(III) phosphide

(b) mercury(II) sulfide

(c) manganese(II) phosphate

(d) copper(I) oxide

(e) chromium(VI) fluoride


(a) CrP; (b) HgS; (c) Mn 3 (PO 4 ) 2 ; (d) Cu 2 O; (e) CrF 6

Got questions? Get instant answers now!

Erin brokovich and chromium contamination

In the early 1990s, legal file clerk Erin Brockovich ( [link] ) discovered a high rate of serious illnesses in the small town of Hinckley, California. Her investigation eventually linked the illnesses to groundwater contaminated by Cr(VI) used by Pacific Gas&Electric (PG&E) to fight corrosion in a nearby natural gas pipeline. As dramatized in the film Erin Brokovich (for which Julia Roberts won an Oscar), Erin and lawyer Edward Masry sued PG&E for contaminating the water near Hinckley in 1993. The settlement they won in 1996—$333 million—was the largest amount ever awarded for a direct-action lawsuit in the US at that time.

Figure A shows a photo of Erin Brockovich. Figure B shows a 3-D ball-and-stick model of chromate. Chromate has a chromium atom at its center that forms bonds with four oxygen atoms each. Two of the oxygen atoms form single bonds with the chromium atom while the other two form double bonds each. The structure of dichromate consists of two chromate ions that are bonded and share one of their oxygen atoms to which each chromate atom has a single bond.
(a) Erin Brockovich found that Cr(VI), used by PG&E, had contaminated the Hinckley, California, water supply. (b) The Cr(VI) ion is often present in water as the polyatomic ions chromate, CrO 4 2− (left), and dichromate, Cr 2 O 7 2− (right).

Chromium compounds are widely used in industry, such as for chrome plating, in dye-making, as preservatives, and to prevent corrosion in cooling tower water, as occurred near Hinckley. In the environment, chromium exists primarily in either the Cr(III) or Cr(VI) forms. Cr(III), an ingredient of many vitamin and nutritional supplements, forms compounds that are not very soluble in water, and it has low toxicity. But Cr(VI) is much more toxic and forms compounds that are reasonably soluble in water. Exposure to small amounts of Cr(VI) can lead to damage of the respiratory, gastrointestinal, and immune systems, as well as the kidneys, liver, blood, and skin.

Despite cleanup efforts, Cr(VI) groundwater contamination remains a problem in Hinckley and other locations across the globe. A 2010 study by the Environmental Working Group found that of 35 US cities tested, 31 had higher levels of Cr(VI) in their tap water than the public health goal of 0.02 parts per billion set by the California Environmental Protection Agency.

Questions & Answers

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Archie Reply
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What is a mole?
Henry Reply
pls give me 3 type of transition metal
Destiny Reply
Copper, Scandium, Vanadium, Iron, Chromium, Cobalt
ion zinc hydrogen
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how do I name compounds
Stanley Reply
depends on the compound. as you may know there's transition metal compounds and there's organic compounds and so on and so forth.
what is electricity
Lorrita Reply
electricity refers to the flow electrons
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Gift Reply
When 1 or 2 chemicals react, they rearrange their atomic composition forming new compounds. The total mass before and after is the same/ constant. Chemical equations of same reactants react in same ratios e.g. 1 Na ion reacts with 1 water molecule or a multipier like 1 mole of Na ions react with 1
Mole of water molecules. In that example we multipied by 6.02*10^23 or avogadro constant (L). Or 2 Na+ ions with two water molecules. The arrow means '' to form '' Some times conditions or reactants are written above the arrow like H+ or enzyme or temper, sometimes physical states are written
Beside the chemical Aqueous (aq) which means solute dissolved on water. Solid (s) etc Some chemical equations are written next to it ΔH= # which means enthalpy change which describes if the reaction is endothermic (+) or exothermic (-).
Some are reversible and have half double arrow sign.
what is the meaning of atoma
Ibrahim Reply
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Michael Reply
what is chemical compound
A compound is the result of chemical bonding between 2 or more different elements.
Why is an atom electrically neutral?
the same number of electron , proton present in an atom.thats why it is electrically neutral
difference between Amine and amide
Amadu Reply
what is the difference between alkanal and alkanone
difference between alkanol and alkanal
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is organic compounds used for drying agent
Olawale Reply
Sulfuric acid is used as a drying agent.
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John Reply
An atom is the smallest part of an element, for instance gold atoms are the smallest part of gold that can enter a reaction. An atom must consist protons and electrons of equal number. You can think of those subatomic particles as spheres, but not orbiting randomly they move in specific way in
That was partially described mathematically. As a muslim, we believe that god created all matter from nothing. He is the Able, and only who can create matter in the begging in the big bang that was described in the Quran in chapter 17 verse 30, 1400 years ago, you can read it from internet.
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Olubodun Reply
Proton donor (H+). Like in lemons, oranges and some medicines.
what is titration? and how can i get my readings?
favor Reply
what is electrolysis?
favor Reply
what is the formula you use when calculating for gas law?
electro-means electricity while lysis-means splitting up so electrolysis simply means splitting up by means of electric current
good day. how may I see previous question asked in this chat, please?
Asha, A person named Favor asked what is meant by the term electrolysis
Practice Key Terms 4

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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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