1.6.2Principles of Chemistry
Common Ions — Edexcel International GCSE Science Double Award 4SD0 - Chemistry Revision Notes & Topical Questions
5 min read 11 parts Lesson 35 of 50
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 5Predicting simple ions from the periodic table
| Group | Outer electrons | Change | Ion charge | Examples |
|---|---|---|---|---|
| 1 | 1 | Lose 1 | 1+ | Li+, Na+, K+ |
| 2 | 2 | Lose 2 | 2+ | Mg2+, Ca2+, Ba2+ |
| 3 | 3 | Lose 3 | 3+ | Al3+ |
| 6 | 6 | Gain 2 | 2− | O2−, S2− |
| 7 | 7 | Gain 1 | 1− | F−, Cl−, Br−, I− |
Part 2 of 5Ions you must simply remember
Transition metal ions
- Transition metal ions These do not follow the group pattern and can have more than one charge.
- Common ones are Fe2+ and Fe3+, Cu2+, Zn2+ and Ag+;
- the Roman numeral in a name, such as iron(III), gives the charge.
Hydrogen and metal-like ions
- Hydrogen and metal-like ions Hydrogen forms H+ in acids.
- Ammonium, NH4+, is a positive ion made of non-metals.
Hydroxide
- Hydroxide The hydroxide ion, OH−, is found in alkalis and metal hydroxides.
Part 3 of 5Compound (molecular) ions
| Name | Formula | Charge |
|---|---|---|
| Hydroxide | OH− | 1− |
| Nitrate | NO3− | 1− |
| Carbonate | CO32− | 2− |
| Sulfate | SO42− | 2− |
| Ammonium | NH4+ | 1+ |
Part 4 of 5Naming negative ions
-ide endings
- -ide endings A single non-metal atom that has gained electrons ends in -ide: chloride, bromide, oxide, sulfide.
-ate endings
- -ate endings Ions that contain oxygen along with another element end in -ate: sulfate, nitrate, carbonate.
- Hydroxide is an exception that ends in -ide.
Group of atoms, one charge
- Group of atoms, one charge In a compound ion the charge belongs to the whole group, not to a single atom,
- which is why the brackets matter in later formulae.
Part 5 of 5Memory strategies
1
Learn the group pattern first: groups 1, 2 and 3 form 1+, 2+ and 3+ ions, and groups 6 and 7 form 2− and 1− ions.
2
Learn the five compound ions in the table, grouping them by charge: two with 1− (hydroxide, nitrate), two with 2− (carbonate, sulfate) and one with 1+ (ammonium).
3
Attach each transition metal to its usual charge, remembering that Fe and Cu can differ.
4
Test yourself by covering a column of the tables and writing it from memory.
Key terms
| Term | Meaning |
|---|---|
| Cation | A positive ion. |
| Anion | A negative ion. |
| Compound ion | A group of covalently bonded atoms that carries an overall charge, such as sulfate. |
| Transition metal | A metal in the central block of the periodic table, often forming ions with different charges. |
| Roman numeral | A number in brackets in a name that shows the charge on a metal ion, as in copper(II). |
Avoid these mistakes
1
Writing the nitrate ion as NO32−. It has a 1− charge, whereas carbonate and sulfate are 2−.
2
Assuming all transition metals form the same charge. Check the Roman numeral in the name.
3
Forgetting that ammonium is positive, even though it contains only non-metals.
4
Confusing sulfide (S2−) with sulfate (SO42−).
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