Grade 9 · Ions and Our Health · Ions
Cations and Anions
Naming, writing and predicting the charges of positive and negative ions.
Learning objectives
- Write correct symbols for common ions.
- Predict ion charge from group number.
- Explain why metals form cations and non-metals form anions.
NGSS alignment
HS-PS1-1
Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.
HS-PS1-2
Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.
HS-PS1-3
Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.
MYP criteria
- Criterion A — Knowing and Understanding
ENGAGE
Two ions, two very different jobs
EXPLAIN
Naming and writing ions
Cations are positive and keep the element name (sodium ion, Na+). Anions are negative and usually end in -ide (chloride, Cl-).
| Group | Typical ion | Charge | Type |
|---|---|---|---|
| 1 | Na+, K+, Li+ | 1+ | Cation |
| 2 | Mg2+, Ca2+ | 2+ | Cation |
| 16 | O2-, S2- | 2- | Anion |
| 17 | F-, Cl-, Br- | 1- | Anion |
Shortcut
For main-group elements, group 1 and 2 metals lose electrons; groups 16 and 17 non-metals gain electrons to complete their outer level.
Interactive simulation · PhET
Build an Atom
Make one cation and one anion, then compare their charges.
While you explore
- Which particle changes to form an ion?
- Why are metals more likely to form cations?
Practice questions
0/2 correct
Level 1
Which of these is a cation?
Level 2
An element in group 16 usually forms an ion with which charge?
Reflect & track
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