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Chapter 20 Section 3

Chapter 20 Section 3. Writing Formulas and Naming Compound. Binary Ionic Compounds. Binary compound – a compound that is composed of two elements Before you can write its formula, you need to know… Which elements are involved Oxidation number. Oxidation Numbers.

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Chapter 20 Section 3

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  1. Chapter 20 Section 3 Writing Formulas and Naming Compound

  2. Binary Ionic Compounds • Binary compound – a compound that is composed of two elements • Before you can write its formula, you need to know… • Which elements are involved • Oxidation number

  3. Oxidation Numbers • Oxidation number – positive or negative number that indicates how many electrons an atom has gained, lost, or shared to become stable • For ionic compounds the oxidation number is the same as the charge on the ion 1+ 0 2+ 3+ 4+ 3- 2- 1-

  4. Compounds Are Neutral • Although individual ions in a compound carry charges, the compound itself is neutral • The number of negative charges must equal the number of positive charges • Practice • Sodium and chlorine • Calcium and fluorine • Aluminum and oxygen

  5. Writing Formulas (Binary Compounds) • Write the symbol of the element with a positive oxidation number • Write the symbol of the element with a negative oxidation number • The charge (without the sign) of one ion becomes the subscript of the other ion. Reduce the subscripts to the smallest whole numbers that retain the ratio of ions

  6. Writing Names (Binary Compounds) • Write the name of the positive ion • Check to see if the positive ion is capable of more than one oxidation number • Write the root name of the negative ion (ex – “chlor” for chlorine or “ox” for oxygen) • Add “ide” to the end of the root name Practice CuCl CuO AlCl3

  7. Compounds with Complex Ions • Not all compounds are binary • Baking soda is NaHCO3 • Polyatomic ions – a positively or negatively charged, covalently bonded group of atoms • To create the name, write the name of the positive ion and follow it with the name of the negative polyatomic ion • Practice • K2SO4 • Sr(OH)2

  8. Writing Formulas (Polyatomic Ions) • Follow the rules for binary compounds, except… • When more than one polyatomic ion is needed, write parentheses around the polyatomic ion before adding the subscript • Practice • Barium chlorate • Ammonium phosphate

  9. Compounds with Added Water • Hydrate – a compound that has water chemically attached to its ions and written into its chemical formula • Before water is added • CoCl2 • Anhydrous (Cobalt chloride) • After water is added • CoCl2●6H2O • Cobalt chloride hexahydrate

  10. Naming Binary Covalent Compounds • Formed between nonmetals • Some elements may form more than one compound • N2O, NO, NO2, N2O5 • They would all be named the same with the ionic system! • Naming covalent compounds uses prefixes • N2O is dinitrogen oxide (or monoxide) • Practice • Also used for hydrates

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