NIS – CHEMISTRY

Lecture 34Formulas for Ionic Compounds

Ozgur Unal

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Formulas for Ionic CompoundsWhat do these formulas tell you about the ions in the compound?NaCl MgCl2Ca3(PO4)2In 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.

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Formulas for Ionic CompoundsBinary 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 7.7The 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.

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Formulas for Ionic CompoundsFormulas 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+a reacts with Y-b.

The ionic compound formed by these ions is: XbYa.

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Formulas for Ionic CompoundsMany 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.Because a 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.

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Formulas for Ionic CompoundsExample: The compound formed by NH4+ and O-2 is (NH4)2O.

Example: A compound formed by calcium ions and phosphate ions is often used in fertilizers. Write the compound’s formula.

Example: Write the formula of the ionic compound formed by sodium and nitrate.

NIS – CHEMISTRY

Lecture 35Names for Ions and Ionic Compounds

Ozgur Unal

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Names for Ions and Ionic CompoundsNaCl MgCl2Try to name these ionic compounds

KH2PO4 Na2S2O3 (NH4)2OTry 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.

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Naming an OxyanionAn 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- PerchlorateNO2- Nitrite ClO3- ChlorateSO4-2 Sulfate ClO2- ChloriteSO3-2 Sulfite ClO- HypochloriteBrO3- BromateIO4- Periodate IO3- Iodate

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Naming Ionic CompoundsFollow 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 of the polyatomic ion.

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Naming Ionic CompoundsExamples:

NaCl Sodium ChlorideMgCl2 Magnesium ChlorideFeO Iron (II) oxideFe2O3 Iron (III) oxide(NH4)2S Ammonium SulfideNaOH Sodium HydroxideCu(NO3)2 Copper (II) NitrateKClO4 Potassium Perchlorate