Chapter 7 : Ionic Compounds And MetalsSection3 :Names and formulas of ionic

compounds

Objectives Relate a formula unit of an ionic compound to its composition.

Write formulas for ionic compounds and oxyanions

What are the names of the following compounds?

NaCl MgCl2

Formulas for Ionic Compounds:1. formula unit represents the simplest ratio of the ions

involved.For example, the formula unit of magnesium

chloride is MgCl 2 because the magnesium and chloride ions

exist in a 1:2 ratio. The overall charge of a formula unit is zero

It contains one Mg 2+ ion and two Cl - ions, for a total charge of zero.

Monatomic ion: is a one-atom ion, such as Mg 2+ or Br -

What is the formula for the calcium ion ? , sulfide ion? And hydrogen ion ?.

Table 7 indicates the charges of common monatomic ions

Oxidation numbers: The charge of a monatomic ion is equal to its oxidation number, or oxidation state.The oxidation number of an element in an

ionic compound equals the number of electrons transferred from the atom to anther.

For calcium floride

So ,Ca =2+ , F=1-

Transition metals . As shown in Table 8, most transition metals

and group 13 and 14 metals have more than one possible ionic charge.

Chemical formulas 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. If no subscript is written, it is assumed to be one.

Formulas for polyatomic ionic compounds:polyatomic ions are ions made up of more

than one atompolyatomic ion acts as an individual ion

Formulas for polyatomic ionic compounds:Thus, the formula for a polyatomic compound follows the same rules used for a binary compounds

Write the formula for the ionic compound formed from ammonium ion(NH4) and oxide ion (O 2- ) ?

Names for Ions and Ionic Compounds

An oxyanion is a polyatomic ion composed of an element, usually a nonmetal, bonded to one or more oxygen atoms.

For example

Now , what are sthe formulas for sodium nitrite, sodium sulfate and calcium

sulfite?

halogen oxynions have a special ruleschlorine forms four oxyanions

Are named according to the number of

oxygen atoms presentAs shown in Table 11Names of similar oxyanions formed

by other halogens follow the rules used for chlorine

For example, bromine forms (Br O 3 - )which is ………, and iodine forms the periodate ion (……..)

five rules for Naming ionic compounds 1. Name the cation followed by the anion.

Remember that the cation is always written first in the formula

2. For monatomic cations, use the element name.

3. For monatomic anions, use the root of the element name plus the suffix -ide.

Example:CsBr Cesium bromide

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.• For example : • F e 2+ and O 2- ions form FeO, known as

iron(II) oxide.• F e 3+ and O 2- ions form F e 2 O 3 ,

known as iron (III) oxide. 

Naming ionic compounds

Naming ionic compounds

5. When the compound contains a polyatomic ion, simply name the cation followed by the name of the polyatomic ion.

Examples:The name for NaOH is sodium hydroxide.The name for (N H 4 ) 2 S is ammonium

sulfide.