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WRITING IONIC FORMULAS

WRITING IONIC FORMULAS. Write the symbol for the cation, then the symbol for the anion. Balance the charges - use the crisscross method - by placing subscripts and “( )” for polyatomic ions if needed. Monatomic ions don’t need “( )”.

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WRITING IONIC FORMULAS

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  1. WRITING IONIC FORMULAS • Write the symbol for the cation, then the symbol for the anion. • Balance the charges - use the crisscross method - by placing subscripts and “( )” for polyatomic ions if needed. • Monatomic ions don’t need “( )”. • Net charges must be zero. Use ion sheet to get charges.

  2. DETERMINING THE CHARGE Monotomic Ions • An ion with only one atom; Mg+2, Na+1, O-2 • Most of the charges can be determined by the atom’s position on the periodic table. • It is the atom’s oxidation number. • Most transition elements have more than one oxidation number (see back of PT or cover of textbook)

  3. DETERMINING THE CHARGE Polyatomic Ions • An ion made up of more than one atom NH4+1, SO4-2, C2H3O2-1; • The charges given to polyatomic ions apply to the whole group of atoms. • NEVER change the subscripts of a polyatomic ion. • If more than one ion is needed, a parenthesis is placed around the ion and the subscript is written outside; Example: Al(OH)3

  4. Criss Cross for writing formulae • Determine the charges on the atoms in the formula • +ve Cation listed first and –ve Anion listed second • Criss Cross the charge each and use the charge as the subscript of the other.

  5. Ex. Aluminum chloride. Al and Cl. • What charge does Al get? +3 Cl ? -1 • Let’s write them down Al3+ Cl1- Al3 Cl1 Don’t need to record “1”s • Step 2 to get the neutral formula AlCl3 • Check to see if formula is neutral +3 -1 -1 -1 = 0 • Remember that if you have a polyatomic ion there will be a few atoms grouped together that have a charge together. So use parenthesis.

  6. MULTIPLE OXIDATION NUMBERS Cations can have more than one oxidation number. Example: Cu+1 and Cu+2. It is important to distinguish which ion is in the compound. There are two ways used in chemistry.

  7. MULTIPLE OXIDATION NUMBERS Stock SystemClassical (Latin) Cu+1 copper (I) cuprous Cu+2 copper (II) cupric Sn+2 tin(II) stannous Sn+4 tin (IV) stannic Hg2+2 mercury (I) mercurous Hg+2 mercury (II) mercuric The lower charge ends in –ous and the higher charge ends in –ic.

  8. MULTIPLE OXIDATION NUMBERS You are only responsible for only the Stock system but I just wanted you to see the other.

  9. MULTIPLE OXIDATION NUMBERS You are only responsible in class for the Stock system but I wanted to make you familiar with the classic.

  10. Examples cupric sulfate/copper (II) sulfate CuSO4 ferrous oxide/iron (II) oxide FeO cobaltic chloride/cobalt (III) chloride CoCl3 mercurous nitrate/mercury (I) nitrate Hg2(NO)2

  11. PRACTICE • lithium fluoride • magnesium chloride • calcium bromide • lithium iodide • lithium oxide • calcium sulfate • barium cyanide • Iron (II) oxide • barium sulfate • aluminum oxide

  12. PRACTICE • sodium nitrate • iron(III) sulfate • copper (II) sulfite • tin (IV) fluoride

  13. PRACTICE • lithium fluoride LiF • magnesium chloride MgCl2 • calcium bromide CaBr2 • lithium iodide LiI • lithium oxide Li2O • calcium sulfate CaSO4 • barium cyanide BaCN • Iron (II) oxide FeO • barium sulfate BaSO4 • aluminum oxide Al2O3

  14. PRACTICE • sodium nitrate NaNO3 • iron(III) sulfate Fe2(SO4)3 • copper (II) sulfite CuSO3 • tin (IV) fluoride SnF4

  15. WRITING FORMULAS • Potassium fluoride • Potassium iodide • Potassium iodate 11. Iron (II) hydroxide • Beryllium chloride 12. Iron (III) oxalate • Beryllium oxide. • Beryllium nitride • Beryllium hydroxide • Sodium acetate • Sodium sulfate • Copper (II) sulfate

  16. Putting It Altogether You need to make sure that you can distinguish between ionic, covalent, and acid compounds.

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