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NIS – CHEMISTRY

NIS – CHEMISTRY. Lecture 34 Formulas for Ionic Compounds Ozgur Unal. Formulas for Ionic Compounds. In this lesson we will find out how to determine the formulas for ionic compounds.

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NIS – CHEMISTRY

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  1. NIS – CHEMISTRY Lecture 34 Formulas for Ionic Compounds OzgurUnal

  2. Formulas for Ionic Compounds • In this lesson we will find out how to determine the formulas for ionic compounds. • The chemical formula of an ionic compound, also called a formula unit, represents the simplest ratio of the ions involved. • Example: MgCl2 contains 1 Mg ion and 2 Chloride ions. • The total charge of MgCl2 is zero. • 1 Mg+2 and 2 Cl- form MgCl2. What do these formulas tell you about the ions in the compound? NaCl MgCl2 Ca3(PO4)2

  3. Formulas for Ionic Compounds Binary ionic compounds are composed of positively charged monoatomic ions of metal and negatively charged monoatomic ions of nonmetal. A monoatomic ion is a one-atom ion, such as Mg+2 and Br-. Check out Table 7.7 • The charge of a monoatomic ion is known as its oxidation number. • The oxidation number of an element in an ionic compound equals the number of electrons transferred from the atom to form the ion. • Example:NaCl. Na transfers one electron to Cl. • Oxidation number of Na is +1. • Oxidation number of Cl is -1.

  4. Formulas for Ionic Compounds Formulas for binary ionic compounds: In the chemical formula for any ionic compound, the symbol of the cation is always written first, followed by the symbol of the anion. Subscripts, which are small numbers to the lower right of a symbol, represent the number of ions of each element in an ionic compound. Ionic compounds have no charge: If you add the oxidation number of each ion multiplied by the number of these ions in a formula unit, the total must be zero. • Example:X+areacts with Y-b. • The ionic compound formed by these ions is: XbYa.

  5. Formulas for Ionic Compounds Many ionic compounds contain polyatomic ions, which are made up of more than one atom. Examples: OH- H2PO4- S2O3-2 O2-2 A polyatomic ion acts as an individual ion in a compound and that its charge applies to the entire group of atoms. Thus, the formula for a polyatomic compound follows the same rules used for a binary compound. • Becausea polyatomic ion exists as a unit, never change subscripts of the atoms within the ion. • If more than one polyatomic ion is needed, place parantheses around the ion and write the appropriate subscript outside the parantheses.

  6. Formulas for Ionic Compounds • Example: A compound formed by calcium ions and phosphate ions is often used in fertilizers. Write the compound’s formula. Example: The compound formed by NH4+and O-2is (NH4)2O. • Example: Write the formula of the ionic compound formed by sodium and nitrate.

  7. NIS – CHEMISTRY Lecture 35 Names for Ions and Ionic Compounds OzgurUnal

  8. Names for Ions and Ionic Compounds • KH2PO4 Na2S2O3 (NH4)2O • Try to name these ionic compounds. NaCl MgCl2 Try to name these ionic compounds • It is hard to call the ionic compounds using the names of the atoms in the compound. • In this lesson we will learn how to name ionic compounds.

  9. Naming an Oxyanion An oxyanion is a polyatomic ion composed of an element, usually nonmetal, bonded to one or more oxygen atoms. Example: SO3-2, NO2-etc. There can be more than one oxyanion for some nonmetals. Check out Table 7.10 for N and S, and Table 7.11 for Cl • Example: • NO3- Nitrate ClO4-  Perchlorate • NO2- Nitrite ClO3-  Chlorate • SO4-2 Sulfate ClO2-  Chlorite • SO3-2  Sulfite ClO- Hypochlorite • BrO3-  Bromate • IO4-  Periodate IO3-  Iodate

  10. Naming Ionic Compounds Follow the five rules: 1- Name the cation followed by the anion. Remember that the cation is always written first in the formula. 2- For monoatomic cations, use the element name. 3- For monoatomic anions, use the root of the element name plus the suffix –ide. 4- To distinguish between multiple oxidation numbers of the same element, the name of the chemical formula must indicate the oxidation number of the cation. Oxidation number is written as a Roman numeral in parantheses after the name of the cation. 5- When the compound contains a polyatomic ion, simply name the cation followed by the name ofthe polyatomic ion.

  11. Naming Ionic Compounds Examples: NaCl  Sodium Chloride MgCl2  Magnesium Chloride FeO  Iron (II) oxide Fe2O3  Iron (III) oxide (NH4)2S  Ammonium Sulfide NaOH  Sodium Hydroxide Cu(NO3)2  Copper (II) Nitrate KClO4  Potassium Perchlorate

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