In this lesson we will learn how ionic formulas reflect the ratio of positive and negative ions in ionic compounds.
By the end of this lesson you will be able to:
- Write the formula for ionic compounds containing only monatomic ions.
- Write the formula for ionic compounds containing polyatomic ions.
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- Although ionic compounds are composed of charged particles (ions), they have no overall charge.
- This is because the total amount of positive charge equals the total amount of negative charge.
- The formulas for ionic compounds do not represent molecules – they represent the ratio of positive and negative ions in the compound’s lattice structure.
- The ‘drag-and-drop’ method is a shorthand way of determining the formula for ionic compounds.
- It involves ‘dragging’ the number in front of each ion and ‘dropping’ it on the bottom right side (subscript) of the other ion.
- When there is more than one copy of a polyatomic ion in a formula, it needs to have brackets around it.
- When the size of the charge is the same for each ion in a compound (+1 and –1, +2 and –2, or +3 and –3), the drag-and-drop rule does not apply.
- The formula of the compound is simply a 1:1 ratio of the two ions.
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(Header image: Hanna, Adobe Stock)