Module 6: Lesson 3: Names & Formula for Ionic Compounds (pg 180)

​Module 6: Ionic Compounds and Metals (Notes)

Lesson 3: Names and Formula for Ionic Compounds (pg 180)

By Catherine LaFever

​A. Formulas for Ionic Compounds

The chemical formula for an ionic compound, called a FORMULA unit, represents the simplest ratio of the ions involved.

Example:

The formula unit of magnesium chloride is MgCl₂ because the magnesium and chloride ions exist in a 1:2 ratio.

The formula unit for MgCl₂ contains one Mg²⁺ ion and two Cl^– ions, for a total charge of zero.

Multiple Choice

calcium hydroxide - Ca(OH)₂

• atom

• molecule

• formula unit

Multiple Choice

dinitrogen trioxide - N₂O₃

• atom

• molecule

• formula unit

Multiple Choice

argon - Ar

• atom

• molecule

• formula unit

​B. Monatomic Ions:

A monatomic ion is a one-atom ion, such as Mg²⁺ or Br^–.

The table to the right gives the charges of common monatomic ions according to their location on the periodic table.

C. Oxidation Numbers:

The oxidation number of a monatomic ion, also called its oxidation state, is equal to the net charge on the ion.

D. Writing Formulas for Binary Ionic Compounds (BICs)

1. Write the cation (metal ion) first and the anion (nonmetal ion) second.

2. Determine the smallest whole number ratio of cations to anions that would make the charge 0.

D. Writing Formulas for Binary Ionic Compounds (BICs)

Main Group Element - To determine the ion formed for main group elements look at its placement on the periodic table.

Transition Metals - any elements in groups 3-12 have either a +2 or +3 charge. For now some will have to be memorized. Noble gasses do not form ions except in rare cases. **Hydrogen can either gain, lose, or share an electron depending on the other elements with which it combines.

D. Writing Formulas for Binary Ionic Compounds (BICs)

D. Writing Formulas for Binary Ionic Compounds (BICs)

D. Writing Formulas for Binary Ionic Compounds (BICs)

TRY THESE EXAMPLES ON YOUR OWN

Multiple Choice

Na ⁺  and  S ^-2

• Na₂S
• NaS₂
• Na₂S₂
• NaS

Multiple Choice

K ⁺  and  N^-3

• KN
• KN₃
• K₃N₃
• K₃N

Multiple Choice

What is the correct formula for aluminum sulfide

• Al₂S₃

• Al₃S₂

• AlS

• S₂Al₃

Multiple Choice

What is the formula for magnesium sulfide?

• Mg₂S₂

• MgS

• SMg

• S₂Mg₂

E. Writing Names for Binary Ionic Compounds (BICs)

There are two naming systems currently acceptable:

1. IUPAC – International Union of Practical and Applied Chemistry is the newest system-this system uses Roman numerals to give the charges or oxidation number of positive ions ONLY if the positive ion has variable charges. This is the system we will use.

2. Example: Copper I or Copper II

E. Writing Names for Binary Ionic Compounds (BICs)

There are two naming systems currently acceptable:

1. “ous” and “ic” system – oldest system and still very commonly used. May be used ONLY if the positive ion has a variable charge and exhibits only 2 oxidation numbers.

2. Example Cuprous and Cupric

   1. The correct full name of the cation (metal ion) is written first. (Do not forget about the roman numerals if it is a Cu, Fe, Sn, or Pb ion!)

   2. The last syllable in the anion (nonmetal ion) is dropped and –ide is added.

E. Writing Names for Binary Ionic Compounds (BICs)

There are two naming systems currently acceptable:

1. “ous” and “ic” system – oldest system and still very commonly used. May be used ONLY if the positive ion has a variable charge and exhibits only 2 oxidation numbers.

2. Example Cuprous and Cupric

   1. The correct full name of the cation (metal ion) is written first. (Do not forget about the roman numerals if it is a Cu, Fe, Sn, or Pb ion!)

   2. The last syllable in the anion (nonmetal ion) is dropped and –ide is added.

E. Writing Names for Binary Ionic Compounds (BICs)

E. Writing Names for Binary Ionic Compounds (BICs)

TRY THESE EXAMPLES ON YOUR OWN

Multiple Choice

 Li₂O

• Dilithium oxideDilithium oxide
  
• Lithium oxide
• Lithium dioxide

Multiple Choice

CsCl

• Monocesium monochloride
• Cesium monochloride
• Cesium Chloride

Multiple Choice

MgS 

• Magnesium sulfide
• Monomagnesium monosulfide
• Magnesium monosulfide

Multiple Choice

Al₂S₃

• Dialuminum Trisulfide
• Aluminum sulfide

Multiple Choice

What is the correct chemical formula for nickel (II) nitride?

• NiN
• Ni(NO₃)₂
• NiNO₃
• Ni₃N₂

F. Nomenclature – Ternary Ionic Compounds

Ternary Ionic Compounds – these are compounds containing polyatomic ions (It is imperative that you know the correct charges on these ions!!!!!)

Polyatomic Ions-two or more elements (usually nonmetals) bonded together that have collectively lost or gained electrons and now have a charge.

Examples:

• ammonium ion (NH⁴⁺)

• phosphate ion (PO₄^3-)

G. Writing Formulas for Ternary Ionic Compounds (TICs)

Compounds have a zero charge but a polyatomic ion has a charge. You must memorize several polyatomic ions (look at the Orange Formula Sheet).

1. Write the cation first and the anion second.

2. Determine the smallest whole number ratio of cations to anions that would make the charge 0. If a subscript must be added to a polyatomic ion, keep the polyatomic ion in parentheses.

G. Writing Formulas for Ternary Ionic Compounds (TICs)

G. Writing Formulas for Ternary Ionic Compounds (TICs)

TRY THESE EXAMPLES ON YOUR OWN

Multiple Choice

Which formula correctly represents the compound magnesium cyanide?

• MgCN

• Mg(CN)₂

• MgCN₂

• Mg₂CN

Multiple Choice

The proper formula for aluminum nitrate:

• AlNO₃
• Al₂(NO₃)₃
• Al(NO₃)₃
• Al₃NO₃

Multiple Choice

The proper formula for tin (IV) sulfite

• Sn₂SO₃
• Sn₂SO₂
• SnSO
• Sn(SO₃)₂

H. Writing Names for Ternary Ionic Compounds (TICs)

1. The correct full name of the cation (metal ion or polyatomic ion) is written first. (Do not forget about the roman numerals if it is a Cu, Fe, Sn, or Pb ion!)

2. The correct full name of the anion (polyatomic ion or nonmetal ion) is written second. If the anion is a polyatomic ion do not change the ending. If the anion is a nonmetal ion then the ending is dropped and –ide is added.

H. Writing Names for Ternary Ionic Compounds (TICs)

TRY THESE EXAMPLES ON YOUR OWN

Multiple Choice

Name the following ionic compound: MgSO₄

• magnesium sulfoxide
• magnesium sulfide
• magnesium sulfate
• magnesium oxide

Multiple Choice

Name the following ionic compound: LiNO₃

• lithium nitrate
• lithium III nitrate
• lithium nitride
• lithium oxide

Multiple Choice

What is the name of the compound Sc(OH)₃?

• Scandium (III) hydroxide

• Scandium (I) hydroxide

• Scandium (II) hydroxide

• Scandium hydroxide

Multiple Choice

Name the following ionic compound: Cr(NO₂)₃

• chromium nitrite
• chromium nitride
• chromium III nitride
• chromium III nitrite

Multiple Choice

What is the name of the compound Na₂(SO₄)?

• Sodium sulfate

• Sodium sulfide

• Sodium sulfite

• Sodium sulfuroxide

J. Writing Names for Hydrates

Hydrated ionic compounds (i.e., hydrates) have a specific number of water molecules in their chemical formulas. In the solid, these water molecules (also called "waters of hydration") are part of the structure of the compound.

A compound with NO water in it is anhydrous, meaning "without water," a term crucial in chemistry for substances that are dry.

Multiple Choice

A compound is a hydrate when it...

• is composed of only hydrogen and oxygen
• is a state of water
• traps water inside of the compound
• repels water from the compound

Multiple Choice

How are anhydrous compounds different from hydrates?

• Anhydrous compounds contain more water molecules than hydrates

• Anhydrous compounds and hydrates are the same

• Anhydrous compounds do not contain water molecules, unlike hydrates

• Anhydrous compounds use Greek letters to indicate the number of water molecules present

J. Writing Names for Hydrates

• Rule 1. The ionic compound (without the waters of hydration) is named first by using the rules for naming ionic compounds (e.g., Ba(OH)₂•8H₂O = "barium hydroxide").

• Rule 2. Greek prefixes are attached to the word "hydrate" to indicate the number of water molecules per formula unit for the compound (e.g., Ba(OH)₂•8H₂O; 8 water molecules = "octahydrate").

J. Writing Names for Hydrates

• Rule 3. When the chemical formula for a hydrated ionic compound is written, the formula for the ionic compound is separated from the waters of hydration by a centered "dot".

J. Writing Names for Hydrates

TRY THESE EXAMPLES ON YOUR OWN

Multiple Choice

What is the correct name for the compound CuSO4·8H2O?

• Copper(I) sulfate octahydrate

• Copper(II) sulfate octahydrate

• Cupric sulfate octahydrate

• Copper(II) sulfate octahydrate

Multiple Choice

Name the following ionic compound: MgSO₄*7H₂O

• magnesium sulfate * hexahydarte
• magnesium sulfate hexahydarte
• magnesium sulfate heptahydrate
• magnesium sulfate* heptahydrate

Multiple Choice

Na₂CO₃ · 10H₂O is known as sodium sulfate ______

• Hydroxide
• Hydrate
• Decahydrate
• None of the above

Multiple Choice

Name the following hydrate:  NaCl * 5H₂O

• sodium chloride 
• sodium monochloride pentahydrate
• sodium chloride pentahydrate
• pentahydrate

K. Writing Formulas for Hydrates

• Rule 1: Include the water at the end of the formula. There is a dot separating the regular compound formula and the water.

• Rule 2: Put a number after the dot and before the H₂O to indicate how many water molecules are associated with the compound.

K. Writing Formulas for Hydrates

TRY THESE EXAMPLES ON YOUR OWN

Multiple Choice

What is the chemical formula for calcium sulfate hexahydrate?

• CaSO₄ * 6H2O

• Ca2(SO4)3 * 6H2O

• Ca(SO4)2 * 6H2O

• Ca3(SO4)3 * 6H2O

Multiple Choice

What is the formula for Copper(II) sulfate pentahydrate?

• CuSO4

• CuSO4·5H2O

• CuSO4·H2O

• Cu2SO4·5H2O

Multiple Choice

What is the chemical formula for magnesium bromide tetrahydrate?

• Mg2Br2·5H2O

• MnBr2·6H2O

• MgBr2·4H2O

• MgBr·3H2O

Multiple Choice

What is the correct formula for Nickel (II) Sulfate dihydrate?

• NiSO4·5H2O

• NiSO4·3H2O

• NiSO4·7H2O

• NiSO4·2H2O

Notes Key for Lesson 3: Names and Formulas for Ionic Compounds