chapter 7.3 names and formulas for ionic compounds

Chapter 7.3

NAMES AND FORMULAS FOR IONIC COMPOUNDS

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

MONATOMIC IONS

• One-atom ions

• Examples: Mg2+, Br -, Al3+, O2-

• Binary ionic compounds are composed of two parts:

1. Positively charged monatomic ion of a metal

2. Negatively charged monatomic ion of a nonmetal

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

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

1 Mg2+ cation 2 Cl - anions

Remember that the overall charge of the compound in

zero (neutral)

POLYATOMIC IONS• Ions containing more than one atom• Examples

• Page 221 Table 7.9

• Make flashcards for every polyatomic ion

• Quizzes on these can occur at any time for the rest of the year

• You must know the names, formulas & charges

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

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 ; SO3

2- = sulfite

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 -

NAMING IONIC COMPOUNDS

1. Name the cation ( + ) followed by the anion ( - )

2. For monatomic cations, use the element name

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

CsBr --- Cesium bromide

NAMING IONIC COMPOUNDS

4. 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

NAMING IONIC COMPOUNDS

5. 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

NaBr

Sodium bromideRoot of the

element Bromine

Ending with -ide

Binary ionic compound:Composed of 2 monatomic ions

Cu(NO3)2

Copper nitrateOxidation number of

copper

Polyatomic anion

Transition metal&

Polyatomic ion

(II)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

Ag2CrO4

Silver chromatePolyatomic

anion

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

NH4ClO4

Ammonium perchloratePolyatomic

anion

TwoPolyatomic ions

Polyatomic cation