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WRITING FORMULAS AND NAMING COMPOUNDS

WRITING FORMULAS AND NAMING COMPOUNDS. Many compounds are ionic. That means they are made up of ions, which are charged particles or charged atoms. Ionic compounds contain one or more positively charged ions and one or more negatively charged ions. RULES FOR WRITING FORMULAS.

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WRITING FORMULAS AND NAMING COMPOUNDS

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  1. WRITING FORMULAS AND NAMING COMPOUNDS Many compounds are ionic. That means they are made up of ions, which are charged particles or charged atoms. Ionic compounds contain one or more positively charged ions and one or more negatively charged ions.

  2. RULES FOR WRITING FORMULAS • Positive and negative charges must balance • Write the symbol of the positive ion first (without the charge) • Write the symbol of the negative ion (without the charge) • Use subscripts to balance the positive and negative charges.

  3. SUBSCRIPTS • A number written to the right and slightly below the symbol of an element indicating how many “atoms” of that element are required to make one neutrally charged “molecule”.

  4. EXAMPLES OF IONIC COMPOUNDS • Make a compound with Ag and Cl • Look on the periodic table to find the charge on an Ag ion and a Cl ion. • Ag is 1+ Cl is 1- • Balance the positive and negative charge with subscripts. • AgCl

  5. EXAMPLES OF IONIC COMPOUNDS • Make a compound with Mg and Cl • Mg 2+ Cl 1- • 1 : 1 ratio will not work • Subscript 2 is needed for the Cl ion. • MgCl2 • Make a compound with chromium III and oxygen. • Cr 3+ O 2- • Subscripts • Find the lowest common multiple between 3 and 2 • 2 X 3 =6 3 X 2 = 6 • Cr2O3

  6. POLY ATOMIC IONS • Ions may be composed of more than one element. • These are called polyatomic ions or radical. • Radicals are groups of atoms that usually remain together during a chemical reaction. • Treat a radical as a single element. • If subscripts are required to balance the charges, the subscript applies to all elements in the radical.

  7. EXAMPLES OF POLYATOMICS • Combine the magnesium ion and the hydroxide ion • Mg 2+ OH 1- • Mg(OH)2 • Parentheses are required on the hydroxide ion in order to distribute the subscript to all atoms in the ion. • Combine ammonium and sulfide • NH4 1+ S 2- • (NH4)2S

  8. TRY THESE • Aluminum and carbonate • Copper II and sulfate • Silver phosphate • Lead II chloride • Ammonium acetate

  9. ANSWERS • Al2(CO3)3 • CuSO4 • Ag3PO4 • PbCl2 • NH4C2H3O2

  10. PREFIX METHOD OF NAMING COMPOUNDS • This method is used when the elements in the compound do not appear to be positive and negative ions. • These are called molecular compounds. • The prefix tells how many atoms of an element are in one molecule of the compound.

  11. 1 mono 2 di 3 tri 4 tetra 5 penta 6 hexa 7 hepta 8 octa 9 nona 10 deca NUMERICAL PREFIXES

  12. MOLECULAR COMPOUND EXAMPLES (PREFIX METHOD) • SO3 sulfur trioxide • N2O3 dinitrogen trioxide • Try these: • PCl3 • CCl4 • CO • CO2

  13. ANSWERS • PCl3 phosphorus trichloride • CCl4 carbon tetrachloride • CO carbon monoxide • CO2 carbon dioxide

  14. RULES FOR NAMING COMPOUNDS • Write the name of the positive ion first including the Roman numeral if appropriate. • Write the name of the negative ion next.

  15. EXAMPLES • NaCl sodium chloride • MgF2 magnesium fluoride (no matter how many negative ions) • Cr2O3 chromium III oxide • Try these: • K2S • CaCO3 • MnCl4

  16. ANSWERS • K2S potassium sulfide • CaCO3 calcium carbonate • MnCl4 manganese IV chloride

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