An ion is an atom that has gained or lost electrons. Electrons are negative, so:
- lose electrons → positive ion (a cation)
- gain electrons → negative ion (an anion)
One way to remember: cation has a t that looks like a plus sign.
The pattern by group
For the main groups you don't need to memorize charges one by one. The column tells you:
| Group | Typical ion | Example |
|---|---|---|
| 1 | +1 | Na⁺ |
| 2 | +2 | Mg²⁺ |
| 13 | +3 | Al³⁺ |
| 15 | −3 | N³⁻ |
| 16 | −2 | O²⁻ |
| 17 | −1 | Cl⁻ |
Metals on the left lose electrons; nonmetals on the right gain them.
Naming
- Positive ions keep the element's name: sodium ion.
- Single-element negative ions end in -ide: chloride, oxide, sulfide.
The exceptions: Roman numerals
Many transition metals can form more than one ion, so the name says which: iron(II) is Fe²⁺ and iron(III) is Fe³⁺; copper(I) is Cu⁺ and copper(II) is Cu²⁺. A few, like silver (Ag⁺) and zinc (Zn²⁺), only form one common ion, so they don't need a numeral.
Why it matters
Ionic compounds balance their charges to zero: Na⁺ and Cl⁻ make NaCl; Mg²⁺ and two Cl⁻ make MgCl₂.