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Writing and Naming Chemical Formulas for Ionic Compounds: Part 1

Writing and Naming Chemical Formulas for Ionic Compounds: Part 1. Science 10. Chemical Formulas. A chemical formula provides you with TWO important pieces of information: 1. The elements that make up the compound. 2. The number of atoms of each element that are present in the

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Writing and Naming Chemical Formulas for Ionic Compounds: Part 1

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  1. Writing and Naming Chemical Formulas for Ionic Compounds: Part 1 Science 10

  2. Chemical Formulas A chemical formula provides you with TWO important pieces of information: 1. The elements that make up the compound. 2. The number of atoms of each element that are present in the compound.

  3. Number of Atoms • In an ionic compound, the formula represents the ratio of each atom present in a compound. • Example: In the compound Li2O, there are 2 lithium atoms for every 1 oxygen atom.

  4. How many atoms are shown? • Example 1:LiNO3 • 5 atoms • Example 2:Mg(OH)2 - 5 atoms • Example 3: (NH4)3PO4 • - 20 atoms

  5. Valence Numbers • We have already used Lewis structures to determine the chemical formulas of compounds, but this can get to be quite tedious (especially with large compounds). • We will now use the shorthand method of determining chemical formulas ~ using combining capacities (AKA: valence numbers).

  6. Valence Numbers (Continued) • A positive valence number indicates the loss of electrons. • A negative valence number indicates the gaining of electrons. • The number next to the + or – indicates HOW MANY electrons are lost or gained to achieve a stable octet, and therefore form a compound.

  7. Writing Chemical Formulas for Simple Ionic Compounds • Write the atom’s symbols with their combining capacities (as superscripts). • Crisscross the combining capacities, and write them (WITHOUT the + or -) as subscripts. • Write the final chemical formula. - If there are any 1’s, remove them. - If the subscripts are multiples of each other, reduce them.

  8. Examples: • calcium fluoride CaF2 2. zinc oxide ZnO 3. Potassium sulphide K2S 4. barium phosphide Ba3P

  9. Naming Simple Ionic Compounds • Write the name of the metal first. • Followed by the name of the non-metal). • Remove the ending of the non-metal and add “ide”.

  10. Examples: • KCl Potassium chloride 2. CaO Calcium Oxide

  11. Multivalent Transition Metals • Are multivalent (have more than one combining capacity or valence) • Roman numerals are used to indicate which combining capacity is to be used

  12. Writing Chemical Formulas for Compounds Containing Transition Metals • Write the atom’s symbols with their combining capacities (as superscripts). - Please note that the combining capacity that you use for the transition metal is indicated by the Roman numeral in the name. 2. Crisscross the combining capacities, and write them (WITHOUT the + or -) as subscripts. 3. Write the final chemical formula. - If there are any 1’s, remove them. - If the subscripts are multiples of each other, reduce them.

  13. Examples: • iron (III) oxide Fe2O3 2. iron (II) oxide FeO 3. Lead (IV) sulphide PbS2 4. mercury (II) oxide HgO

  14. Naming Multivalent Compounds Step 1: Write the names of the metal and non-metal, leaving a space after the metal for a roman numeral Step 2: Reverse ‘criss cross’, this will give you the ion charge of the metal. The non-metal charge is always constant (look at periodic table) Step 3: Write formula including roman numeral for metal. **NOTE watch for reducing**

  15. Example: FeCl3 • Step 1: write names of elements Iron Chloride • Step 2: - reverse criss cross Iron – Ion charge of 3+ (from formula), Chlorine – ion charge of 1- (always and forever) • Step 3: Iron(III)Chloride

  16. Examples: • Fe2O3 - Iron(III)Oxide 2. MnS - Manganese(II)Sulphide 3. MnS2(Watch out for LOWEST TERMS!) - Manganese(IV)Sulphide

  17. Try the Magic Formula!!!! • Fe2O3 Answer - Iron (III) Oxide 2. MnS – watch for reducing – -hint S is always 2- Answer – Manganese (II) Sulphide 3. MnS2 Answer – Manganese (IV)Sulphide – again check for reducing – Sulphide is 2-, Manganese was reduced from 4+

  18. Homework • Do practice problems pages 188,190,191 – copy question on a separate sheet of paper – check answers in back of book • Worksheets • One common ion charge • Multiple ion charges • Mixing it up

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