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Names and formulas for ionic compounds

Names and formulas for ionic compounds. Chapter 7.3. Formulas for ionic compounds. Ionic compounds are made up of ions arranged in a repeating pattern Formula unit: chemical formula for an ionic compound Represents the simplest ratio of the ions involved

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Names and formulas for ionic compounds

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  1. Names and formulas for ionic compounds Chapter 7.3

  2. Formulas for ionic compounds • Ionic compounds are made up of ions arranged in a repeating pattern • Formula unit: chemical formula for an ionic compound • Represents the simplest ratio of the ions involved • Formula unit of magnesium chloride = MgCl2 • Magnesium and chloride ions exist in a 1:2 ratio • Overall charge is zero

  3. Monatomic ions • One-atom ions • Examples: Mg2+, Br-, Al3+, O2- • Binary ionic compounds are composed of two parts: • Positively charged monatomic ion of a metal • Negatively charged monatomic ion of a nonmetal

  4. Oxidation numbers • The charge of a monatomic ion • Example: Mg2+- oxidation number = 2+ • The oxidation number of an element in an ionic compound is the number of electrons transferred from or to the atom to form the ion

  5. Formulas for binary ionic compounds • In the chemical formula for any ionic compound, the symbol of the cation (+) is written first, followed by the symbol of the anion (-) • Subscripts (small numbers on the lower right of the symbol) represent the number of ions of each element in the ionic compound. If no subscript is written, it is assumed to be one. • Example – MgCl2 Remember that the overall charge of the compound in zero (neutral) 1 Mg2+cation 2 Cl - anions

  6. Formulas for polyatomic ionic compounds • Polyatomic ions: made up of more than one atom • A polyatomic ion acts as an individual ion in a compound and its charge applies to the ENTIRE group of atoms • Never change the subscripts of the atoms within the ion • If more than one is needed to form a compound, place parentheses around the ion and write the appropriate subscript outside of the parentheses • Example – Ca(OH)2 1 Ca2+cation 2 OH- polyatomic anions

  7. Names for ions and ionic compounds • Oxyanion: a polyatomic ion composed of an element, usually a nonmetal, bonded to one or more oxygen atoms • Names for oxyanions containing sulfur & nitrogen • Identify the ion with the greatest number of oxygen atoms. This ion is named using the root of the nonmetal and the suffix –ate • Identify the ion with the fewer number of oxygen atoms. This ion is named using the root of the nonmetal and the suffix –ite • Examples: • NO3- = nitrate ; NO2- = nitrite • SO42- = sulfate ; SO32- = sulfite

  8. Names for ions and ionic compounds • Names for oxyanions containing chlorine • Greatest number of oxygen atoms: Perchlorate = ClO4- • One fewer oxygen atom: Chlorate = ClO3- • Two fewer oxygen atoms: Chlorite = ClO2- • Three fewer oxygen atoms: Hypochlorite = ClO-

  9. Naming ionic compounds • Name the cation ( + ) followed by the anion ( - ) • For monatomic cations, use the element name • For monatomic anions, use the root of the element name plus the suffix –ide CsBr --- Cesium bromide

  10. Naming ionic compounds • To distinguish between multiple oxidation numbers of the same element (transition metals), the chemical formula number must indicate the oxidation number of the cation in roman numerals • Applies only to transition metals and metals on the right side of the periodic table (NOT group 1 and group 2 metals) • Fe2+ and O2- form FeO – iron (II) oxide • Fe3+ and O2- form Fe2O3 – iron (III) oxide

  11. Naming ionic compounds • When a compound contains a polyatomic ion, simply name the cation followed by the name of the polyatomic ion • NaOH = sodium hydroxide • (NH4)2S = ammonium sulfide

  12. NaBr Binary ionic compound: Composed of 2 monatomic ions Sodium bromide Ending with -ide Root of the element Bromine

  13. Cu(NO3)2 Transition metal & Polyatomic ion Copper nitrate Check Table 7.8 (page 219) Some metal ions have multiple oxidation numbers. If one does, you must indicate it when naming the compound that it is in (II) Oxidation number of copper Polyatomic anion

  14. Ag2CrO4 Transition metal & Polyatomic ion Check Table 7.8 (page 219) Some metal ions have multiple oxidation numbers. If one does, you must indicate it when naming the compound that it is in Silver chromate Polyatomic anion

  15. NH4ClO4 Two Polyatomic ions Ammonium perchlorate Polyatomic anion Polyatomic cation

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