What Is an Ion Table and How Do You Use It to Find Ion Charges?

Updated

An ion table is a reference that lists common ions alongside their electrical charges, letting you look up the charge an element carries when it gains or loses electrons. You use it by finding the element, reading its listed charge, and then applying that charge to predict ionic compound formulas. It is most useful for main-group elements, where charge often follows a predictable pattern from the periodic table's group number. For transition metals, which can form several different ions, the table is essential because no single group rule applies.

What an Ion Table Shows

A standard ion table organizes ions into two broad categories and typically lists the ion symbol, its name, and its charge.

  • Cations — positively charged ions, formed when an atom loses electrons. Metals dominate this group.
  • Anions — negatively charged ions, formed when an atom gains electrons. Nonmetals dominate this group.

Each entry usually gives the element symbol with its charge as a superscript, such as Na⁺ or Cl⁻. Some tables also include polyatomic ions — groups of atoms that carry a charge as a unit, like SO₄²⁻ (sulfate) or NH₄⁺ (ammonium).

An interactive periodic table, such as Zperiod, presents 118 elements with ion information and 3D atom models, so you can move between the full table and ion data in one workspace. Note that Zperiod's full workspace is described as a desktop experience, with a separate iPhone version.

How to Read an Ion Charge from the Table

The fastest method depends on whether the element is a main-group metal, a nonmetal, or a transition metal.

Main-group metals (cations)

For metals in groups 1, 2, and 13, the most common ion charge follows the group:

Group Typical charge Example
1 1+ Na⁺
2 2+ Mg²⁺
13 3+ Al³⁺

Nonmetals (anions)

For nonmetals, the charge is often the group number minus 8:

Group Typical charge Example
15 3− N³⁻
16 2− O²⁻
17 1− Cl⁻

Transition metals

Transition metals can form more than one ion, so you cannot rely on a group rule. The table lists each common ion separately — for example, iron appears as both Fe²⁺ (iron(II)) and Fe³⁺ (iron(III)). Always check which one the table specifies for the context you need.

Using Ion Charges to Predict Compound Formulas

Once you know the charges, you can build the formula of a simple ionic compound by balancing positive and negative charge so the total equals zero.

Steps:

  1. Write the cation and anion with their charges (for example, Ca²⁺ and Cl⁻).
  2. Find the smallest whole-number ratio that makes the total charge zero.
  3. Use those numbers as subscripts in the formula.

Example: Ca²⁺ and Cl⁻. One Ca²⁺ needs two Cl⁻ to balance (2+ and 2−). The formula is CaCl₂.

Example: Al³⁺ and O²⁻. The least common multiple of 3 and 2 is 6, so you need two Al³⁺ and three O²⁻. The formula is Al₂O₃.

Common Mistakes When Reading Ion Charges

  • Confusing group number with charge. Group 17 elements form 1− ions, not 17− or 7−. The charge comes from how many electrons are gained or lost to reach a stable configuration, not the group number itself.
  • Assuming one charge for transition metals. Iron, copper, and others form multiple ions. Reading only the first entry can give the wrong formula.
  • Ignoring polyatomic ions. Compounds like Ca(NO₃)₂ use a polyatomic ion (NO₃⁻) that must be treated as a single unit, with parentheses when more than one is needed.
  • Dropping the sign. A charge of 2+ is not the same as 2−. Mixing them up reverses the compound.

When to Use an Ion Table

Reach for an ion table when you need to:

  • Find the charge of a specific ion quickly.
  • Predict the formula of an ionic compound.
  • Check whether an element forms more than one ion.
  • Study or review common cations, anions, and polyatomic ions.

For a full set of elements with ion data and 3D models in one place, an interactive periodic table like Zperiod combines the table, ion information, and chemistry tools in a single workspace.