CHAPTER 5: TYPES OF

COMPOUNDS

Section 5.1: Ionic Compounds

Objectives: Apply ionic charge to writing formulas for ionic compounds, Apply formulas to name ionic compounds, Interpret the information in a chemical formula

Ionic Compound Formulas

BINARY COMPOUNDS: Contain only two elements

 

Can contain more than one ion of each element (ex: CaF2), but are not composed of three or more different elements.

Ionic Compound Formulas

Naming Binary Ionic Compounds:

1) Write the name of the positively charged ion (metal)

2) Add the name of the negatively charged ion (nonmetal), modified to end in –ide

Ex: Potassium, Chlorine →

Potassium Chloride

Magnesium, Oxygen → Magnesium Oxide

Ionic Compound Formulas

Try these:

1) Li2O

2) CaCl23) Sulfur and Sodium

4) Potassium and Sulfur

5) Fluorine and Sodium

Formulas for Ionic Compounds

Compounds are electrically neutral – the sums of the charges in an ionic compound equal 0

Add subscripts to the element symbols (ions) until the sum of the ions’ charge is 0.

The smallest subscript is 1. However, no subscript needs to be written - the 1 is understood.

Example: NaCl - 1 Sodium, 1 Chlorine

Formulas for Ionic Compounds

If more than one ion of a given element is in a compound, the subscript indicates how many ions are present

Example: CaF2 - 1 Calcium, 2 Fluorine ions

Formulas for Ionic Compounds

In an ionic compound, a formula represents the smallest ratio of atoms or ions in the compound

Ex. CaF2 not Ca2F4

In a covalent compound, the smallest unit of the compound is a molecule

Ex. H2O

  A formula is the simplest possible ratio of ions

present.

Formulas for Ionic Compounds

FORMULA UNIT: Simplest ratio of ions in a compound.

Charges on Ions

Metals tend to lose electrons and become positive ions

Nonmetals tend to gain electrons and become negative ions

OXIDATION NUMBER: Charge on an ion

Charges on Ions Oxidation numbers for elements are can

be predicted by group number.

Ex: F is in group 17, it gains one outer electron

Al is in group 13, it loses three outer electrons

However, oxidation numbers for elements in groups 3-12 (transition elements) cannot be predicted by group

Get out periodic table and make notes!

Writing a simple formula

Write the formula for an ionic compound containing sodium and sulfur.

1)What are the elements involved?

2) What are the oxidation numbers of each?

3) Sum of the ions must be zero. (add some if necessary

4) Write the symbols and numbers (subscripts) for each element, positive ion (metal) first.

Writing a simple formula

Practice Problems

1) lithium oxide

→ Li2O

2) calcium bromide

→ CaBr2

 3) barium and oxygen

→ BaO

4) strontium and iodine

→ SrI2

Writing a simple formula

More Practice

5) Barium and oxygen

6)Strontium and iodine

7) Lithium and chlorine

8) Radium and chlorine

POLYATOMIC ION

Ion that has 2 or more different elements

  In a polyatomic ion, a group of atoms is

covalently bonded together when the atoms share electrons.

  Although the individual atoms have no

charge the group as a whole has a charge.

Examples: nitrite NO22-, sulfate SO4

2-

POLYATOMIC IONFormulas for polyatomic ions: Treat the polyatomic ion as if it were a single-

element ion by keeping it together as a unit. The sum must equal zero. Multiples of a polyatomic ion in a formula can

be indicated by placing the entire polyatomic ion in parentheses.

Example: Mg(NO3)2

Note: Never change the subscripts within the polyatomic ion

POLYATOMIC ION

Sample problems

1) Write a formula for Li+ and CO32-

Because CO3 has a –2 charge, two Li are needed to balance

Li2CO3

Check charges: 2(1+) +1(2-) = 0 (sum must equal zero)

POLYATOMIC ION

2) Write a formula for Al3+ and SO42-

Find the least common multiple of 2 and 3 → 6

Two Al3+ will be needed: 2 (3+) = 6 Three SO4

2- will be needed: 3 (2-) = -6

Al2(SO4)3

Check charges: 2 (3+) + 3 (2-) = 0

POLYATOMIC ION

3) Ammonium (NH4+) and sulfite (SO32-)

Because SO3 has a –2 charge, two NH4 are needed to balance

(NH4)2SO3

Check Charges: 2 (1+) + 1 (2-) = 0

POLYATOMIC ION

4) Sodium (Na+) and Phosphate (PO43-)

Because PO4 has a –3 charge, 3 Na are needed to balance

Na3PO4

Check Charges: 3 (1+) + 1 (3-) = 0

POLYATOMIC ION

Formulas:

1) Aluminum and cyanide

2) Lithium and peroxide

3) Ammonium and phosphate

4) Calcium and carbonate

5) Rubidium and nitrate

Names:

1) BaSO4 2) MgCO3 3) Li2SO3

4) K3PO4 5) Al(CN)3

Transition Elements

Can have more than one oxidation number, except Zn2+ and Ag+ only have one type of ion

Examples: Cu+ Cu2+ Fe2+ Fe3+

Show Video

Transition Elements

Naming compounds formed from transition elements:

Use a Roman numeral to indicate the oxidation number of the transition element

Roman numerals are placed in parentheses after the name of the element

Examples: Cr2+ Chromium (II)

Cr3+ Chromium (III)

Cr6+ Chromium (VI)

Show Video

Transition Elements

Examples

1) Write the formula for Copper (I) and Sulfite

Cu+ and SO32-

Because SO3 has a –2 charge, 2 Cu will be needed to balance

Cu2SO3

Transition Elements

2) Write the name for Pb(NO3)2

Because NO3 has a –1 charge and there are 2 of them, the oxidation state of Pb must be +2

lead (II) nitrate

Transition Elements

Practice Problems: Gold (III) sulfate Nickel (II) fluoride MnS Cu2SO3

SnF4

Au(CN)3

HYDRATE

Compound in which there is a specific ratio of water to ionic compound

In hydrates, the water molecules are chemically bonded to ionic compounds (• H2O)

Ex CuSO4 • H2O

HYDRATE

HYGROSCOPIC substances: Ionic compounds can easily become hydrates by absorbing water molecules from water vapor in the air

Example: Na2CO3

DELIQUESCENT substances: So hygroscopic that they take up enough water from the air to dissolve completely and form a liquid solution

Example: NaOH

HYDRATE

Compounds that form hydrates are often are used as drying agents (desiccants)

  Heating hydrates can drive off water.

  ANHYDROUS compound: One in which

all of the water has been removed.

 

HYDRATE

To write the formula for a hydrate,

1) Write the formula for the compound

2) Place a dot followed by the number of water molecules per formula unit of compound

Ex. CuSO4 • 5H2O

HYDRATE

To name hydrates,

1) Write the regular name for the compound

2) Use prefix to indicate the number of water molecules present in front of the word hydrate

Ex Copper (II) sulfate pentahydrate

HYDRATEPrefixes to Use in Naming Hydrates:

Molecules of water Prefix

1 mono-

2 di-

3 tri-

4 tetra-

5 penta-

6 hexa-

7 hepta-

8 octa-

9 nona-

10 deca-

 

HYDRATE

Examples: Calcium chloride pentahydrate Aluminum oxide octahydrate Li3N∙ 3H2O

BaS∙ 4H2O

Interpreting Formulas

To represent more than one formula unit of a compound- place a coefficient before the formula

Example: two formula units of NaCl – 2NaCl

 

 

Formulas summarize how many atoms of each element are present:

Examples: (NH4)2SO4

2 N, 8H, 1S, 4O

Interpreting Formulas

Try this: 3Al2(CrO4)3

6 Al, 9 Cr, 36 O

5Ba3(PO4)2

15 Ba, 10 P, 40 O