Ionic Compounds

Cheatsheet Content

### Ionic Compounds Overview Ionic compounds are formed when electrons are transferred from a metal atom to a non-metal atom, creating oppositely charged ions that attract each other. This strong electrostatic force forms an ionic bond. * **Cations:** Positively charged ions (formed by metals losing electrons). * **Anions:** Negatively charged ions (formed by non-metals gaining electrons). ### Common Cations (Positive Ions) These are common positive ions (metals) and their valencies (charge). | Ion Name | Symbol | Valency (Charge) | | :---------- | :---------- | :--------------- | | Sodium | $Na^+$ | 1 | | Potassium | $K^+$ | 1 | | Silver | $Ag^+$ | 1 | | Hydrogen | $H^+$ | 1 | | Ammonium | $NH_4^+$ | 1 | | Magnesium | $Mg^{2+}$ | 2 | | Calcium | $Ca^{2+}$ | 2 | | Zinc | $Zn^{2+}$ | 2 | | Copper(II) | $Cu^{2+}$ | 2 | | Iron(II) | $Fe^{2+}$ | 2 | | Aluminium | $Al^{3+}$ | 3 | | Iron(III) | $Fe^{3+}$ | 3 | | Lead(II) | $Pb^{2+}$ | 2 | ### Common Anions (Negative Ions) These are common negative ions (non-metals or polyatomic ions) and their valencies (charge). | Ion Name | Symbol | Valency (Charge) | | :----------------- | :--------------- | :--------------- | | Chloride | $Cl^-$ | 1 | | Bromide | $Br^-$ | 1 | | Iodide | $I^-$ | 1 | | Fluoride | $F^-$ | 1 | | Hydroxide | $OH^-$ | 1 | | Nitrate | $NO_3^-$ | 1 | | Bicarbonate | $HCO_3^-$ | 1 | | Oxide | $O^{2-}$ | 2 | | Sulphide | $S^{2-}$ | 2 | | Sulphate | $SO_4^{2-}$ | 2 | | Carbonate | $CO_3^{2-}$ | 2 | | Phosphate | $PO_4^{3-}$ | 3 | | Nitride | $N^{3-}$ | 3 | ### Forming Ionic Compounds (Criss-Cross Method) To write the chemical formula for an ionic compound, follow these steps: 1. **Write the symbols** of the cation (metal) first, followed by the anion (non-metal or polyatomic ion). 2. **Write the valency** (charge) of each ion above its symbol. 3. **Criss-cross the valencies:** The numerical value of the cation's valency becomes the subscript for the anion, and the numerical value of the anion's valency becomes the subscript for the cation. Ignore the positive and negative signs. 4. **Simplify and write the formula:** * If the valencies are the same, they cancel out (e.g., $Na^1Cl^1 \rightarrow NaCl$). * If a polyatomic ion requires a subscript greater than 1, enclose the polyatomic ion in parentheses (e.g., $Mg(OH)_2$). * Subscript '1' is usually omitted. **Example: Forming Aluminium Oxide** * **Step 1:** $Al$ (Aluminium) and $O$ (Oxygen) * **Step 2:** $Al^{3+}$ and $O^{2-}$ * **Step 3:** Criss-cross valencies: $Al_2O_3$ * **Step 4:** Final Formula: $Al_2O_3$ ### Examples of Ionic Compounds Here are common ionic compounds, their constituent ions, valencies, and final formulas, similar to what your teacher might ask in the activity. | Compound Name | Cation | Anion | Cation Valency | Anion Valency | Formula | | :-------------------- | :---------- | :-------------- | :------------- | :------------ | :---------------- | | Sodium Chloride | $Na^+$ | $Cl^-$ | 1 | 1 | $NaCl$ | | Magnesium Oxide | $Mg^{2+}$ | $O^{2-}$ | 2 | 2 | $MgO$ | | Aluminium Oxide | $Al^{3+}$ | $O^{2-}$ | 3 | 2 | $Al_2O_3$ | | Calcium Chloride | $Ca^{2+}$ | $Cl^-$ | 2 | 1 | $CaCl_2$ | | Sodium Sulphate | $Na^+$ | $SO_4^{2-}$ | 1 | 2 | $Na_2SO_4$ | | Ammonium Chloride | $NH_4^+$ | $Cl^-$ | 1 | 1 | $NH_4Cl$ | | Magnesium Hydroxide | $Mg^{2+}$ | $OH^-$ | 2 | 1 | $Mg(OH)_2$ | | Iron(III) Chloride | $Fe^{3+}$ | $Cl^-$ | 3 | 1 | $FeCl_3$ | | Potassium Nitrate | $K^+$ | $NO_3^-$ | 1 | 1 | $KNO_3$ | | Calcium Carbonate | $Ca^{2+}$ | $CO_3^{2-}$ | 2 | 2 | $CaCO_3$ | | Aluminium Phosphate | $Al^{3+}$ | $PO_4^{3-}$ | 3 | 3 | $AlPO_4$ | | Zinc Sulphate | $Zn^{2+}$ | $SO_4^{2-}$ | 2 | 2 | $ZnSO_4$ | | Copper(II) Sulphide | $Cu^{2+}$ | $S^{2-}$ | 2 | 2 | $CuS$ | | Sodium Nitride | $Na^+$ | $N^{3-}$ | 1 | 3 | $Na_3N$ | | Lead(II) Sulphate | $Pb^{2+}$ | $SO_4^{2-}$ | 2 | 2 | $PbSO_4$ | | Potassium Bromide | $K^+$ | $Br^-$ | 1 | 1 | $KBr$ | | Magnesium Nitrate | $Mg^{2+}$ | $NO_3^-$ | 2 | 1 | $Mg(NO_3)_2$ | | Calcium Phosphate | $Ca^{2+}$ | $PO_4^{3-}$ | 2 | 3 | $Ca_3(PO_4)_2$ |