6.2: Ions With Variable Charges
- Page ID
- 366502
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)- Given the symbol for a monatomic, variable-charge ion write the systematic name.
- Given the systematic name for a monatomic, variable-charge ion write the symbol.
Up until now, we have looked at elements that form ions with fixed charges. By fixed charge, we mean that we can always predict the charge on the ion. An oxide ion, for example, always has a charge of -2. It is impossible for oxygen to form an ion with a -1 charge or a -3 charge.
Many metals, on the other hand, form ions that have variable charges. Saying an ion has variable charges means that the same element can form ions with different charges. For example, it is possible for copper to form both an ion with a +1 charge and to form an ion with a +2 charge. The large majority of transition metals form ions with variable charges. There is also a small block of main group metals that form ions with variable charges as well (see Figure \(\PageIndex{1}\) below). There is no need to memorize the charges of metals that form ions with variable charges, as the charges may be identified by using Roman numerals. When writing the name of the ion, the name of the metal is immediately followed by parentheses (no space) within which is a Roman numeral equal to the magnitude of charge on the ion.
For example,
- the iron(II) ion has a chemical formula of Fe2+.
- the iron(III) ion has a chemical formula of Fe3+.
Figure \(\PageIndex{1}\): The periodic table showing elements that form ions with variable charges.
For a reminder about how to write Roman numerals, see Table \(\PageIndex{1}\) below. Be especially careful with four (IV in Roman numerals) and six (VI in Roman numerals).
| charge | Roman numeral |
|---|---|
| +1 | I |
| +2 | II |
| +3 | III |
| +4 | IV |
| +5 | V |
| +6 | VI |
Table \(\PageIndex{1}\): Roman numerals used to represent charges.
If the chemical formula of an ion is provided, write the name. If the name of an ion is provided, write the chemical formula.
- Mn3+
- copper(I) ion
- lead(IV) ion
- Cu2+
- Answer A
- manganese(III) ion
- Answer B
- Cu+
- Answer C
- Pb4+
- Answer D
- copper(II) ion
When writing names for compounds containing metals that form ions with variable charges, the name must include the Roman numeral that shows the charge on the metal ion. It is incorrect to use the term chromium ion, for example, since chromium can form both an ion with a +2 charge and an ion with a +3 charge. Roman numerals must not be included when the metal only forms ions with fixed charges. It is not correct, for example, to call a calcium ion a calcium(II) ion. Table \(\PageIndex{2}\) lists the cations that form ions with fixed charges. These need to be memorized.
| ion | charge |
|---|---|
| any group 1 ion | +1 |
| silver ion | +1 |
| any group 2 ion | +2 |
| cadmium ion | +2 |
| zinc ion | +2 |
| aluminum ion | +3 |
| gallium ion | +3 |
| scandium ion | +3 |
Table \(\PageIndex{2}\): Ions with Fixed Charges
If the formula of an ion is provided, write the name. If the name of an ion is provided, write the formula.
- Zn2+
- Co3+
- Sn2+
- Ag+
- Answer A
- zinc ion
- Answer B
- cobalt(III) ion
- Answer C
- tin(II) ion
- Answer D
- silver ion
Contributions & Attributions
- Lance S. Lund (Anoka-Ramsey Community College)
Henry Agnew (UC Davis)