CHEMICAL FORMULAS AND CHEMICAL COMPOUNDS

Chapter 7.1

Objectives:1. Explain the significance of a

chemical formula.2. Determine the formula of an ionic

compound formed between two given ions.

3. Name an ionic compound given its formula.

4. Using prefixes, name a binary molecular compound from its formula.

5. Write the formula of a binary molecular compound given its name.

Chemical names and Formulas There are millions of natural and

synthetic chemical compounds Calcium carbonate – limestone Sodium chloride – table salt Dihydrogen monoxide – water

These are their chemical and common names Chemical names help to describe the atomic

makeup of the compounds

Significance of a Chemical Formula Chemical formula

Indicates the relative number of atoms of each kind in a chemical compound.

Molecular formula Indicates the relative number of atoms of each

kind in a molecule. (Covalently bonded)

C8H18

Subscript indicates there are 8 atoms of carbon in a molecule of octane

Subscript indicates there are 18 atoms of hydrogen in a molecule of octane

Chemical formula for ionic compound Ionic compound consists of lattice of positive and

negative ions held together by mutual attraction. Chemical formula represented by one formula unit

Simplest ratio of the compounds positive and negative ions

Aluminum sulfate below consists of aluminum cations and sulfate ions

Al2(SO4)3

Subscript 2 refers to 2 Aluminum atoms

Subscript 4 refers to 4 oxygen atoms in the sulfate ion

Subscript 3 refers to everything inside the parentheses giving 3 sulfate ions, with a total of 3 sulfur atoms and 12 oxygen atoms

Note: when you only have one of an atom, no subscript is used

Note: parentheses are used to identify polyatomic ion as one unit

Monatomic ions Ions formed from a single atom

Examples Na+1 lose one electron Mg2+

S2- gain two electrons N-3

Cl1-

Not all main-group elements readily form ions Examples

Carbon & Silicon form covalent bonds d-block elements form variable charges

examples Copper, can be Cu+1 or Cu+2 Iron, can be Fe+2 or Fe+3

Lead, can bePb+2, Pb+3, or Pb+4

Naming Monatomic ions Positive ions

Name of element Ex: K+ Potassium

Mg+2 Magnesium Al+3 __________ Sr+2 __________

Negative ions Base of element + -ide ending

Ex: F-1 Fluoride N-3 Nitride

O-2 _______ Br-1 _______

Binary Ionic Compounds Compounds composed of two different

elements Total # of positive charges must be equal

to total # of negative charges Writing formulas, Ex: Aluminum oxide

1. Write the symbols for ions (Cation first)

Al+3 O-2

2. Cross over the charges as subscripts

Al2O3

3. Check to make sure total charges are equal, divide by largest number, to give smallest whole-number ratio

Al2O3

+3 -2

2 x (+3) = +6

3 x (-2) = -6

Naming binary ionic compounds

Nomenclature Naming system

Name Al2O3

Name cation first : full name of cation Aluminum

Name Anion last : base of anion + -ide oxide

Al2O3

aluminum oxide

Practice Naming and Writing Formulas

Name1. AgCl2. ZnO3. SrF2

Write the formulas for1. Zinc iodide2. Zinc sulfide3. Aluminum sulfide

silver chloride

zinc oxide

strontium fluoride

ZnI2

ZnS

Al2S3

Stock System of Nomenclature Some cations may have two or more different charges

Use stock system of naming (usually with d-block elements)

Roman numeral represents charge in parentheses Fe+2 Fe+3

Iron(II) Iron(III)

Some cations that commonly form only one cation Do not use roman numerals ( main group elements)

No Anions form more than one charge

CuCl2+2-1

copper(II)

chloride

Practice stock system Write formula and give name for

compound formed by ions Cr+3 and F-

1 CrF3

chromium(III) fluoride Write formulas and give name for

the following ionic compounds:CuBr2 copper(II)

bromideCu+2 and Br-1

Fe+2 and O-2

Fe+3 and O-2

FeO iron(II) oxide

Fe2O3 iron(III) oxide

Compounds containing Polyatomic Ions

All but NH4+, ammonium ion, are negatively

charged Most are oxyanions

Examples NO3

-1 NO2-1

nitrate nitrite

Most common anion has –ate ending Anion with one less oxygen has –ite ending

Anion with two less oxygen has hypo prefix and –ite ending

Anion with one extra oxygen has per prefix and –ate ending

ClO3-1 ClO2

-1 ClO-1 ClO4-1

chlorate chlorite hypochlorite

perchlorate

Naming Compounds with Polyatomic Ions

Same as naming for ionic compounds except Name polyatomic ion as one unit

Example: AgNO3

Use parentheses if more than one polyatomic ion Example

Al2(SO4)3

silver nitrate

Show 2 Al+3 ions and 3 SO4-

2 ionsaluminum sulfate

Writing Formulas and Naming Compounds with Polyatomic Ions Write the formula for these:

1. tin(IV) sulfate2. calcium chloride3. lithium nitrate4. calcium nitrite5. potassium perchlorate

Write the names for these:1. Ag2O

2. Ca(OH)2

3. NH4OH

4. FeCrO4

5. KClO

silver oxide

calcium hydroxide

potassium hypochlorite

ammonium hydroxideiron(II) chromate

Sn(SO4)2

CaCl2LiNO3

Ca(NO2)2

KClO4

Naming Binary Molecular Compounds May use stock system to name these

New system – must understand oxidation numbers

Prefix system Old system – must know numerical prefixes

1. mono-2. di-3. tri-4. tetra-5. penta-

6. hexa-7. hepta-8. octa-9. nona-10.deca-

Rules for prefix system of Nomenclature

1. less-electronegative element is given first

2. Second element is named by combining

a. Prefix indicating number of atomsb. Root of name of second elementc. -ide ending3. The o or a at the end of a prefix is usually dropped when the word following the prefix begins with another vowel

Ex: P4O10

Ex: tetra

• First element only gets a prefix if it has more than one

phosphorus

dec

oxide

The 6 binary compounds of Nitrogen and Oxygen

N2O

NONO2

N2O3

N2O4

N2O5

dinitrogen

monoxidenitrogen

dinitrogen

dioxidenitrogen

monoxide

dinitrogen

trioxide

tetroxide

pentoxide

dinitrogen•Name the

following molecular compounds1. SO3

2. ICl33. PBr5

1. carbon tetraiodide2. phosphorus

trichloride3. oxygen difluoride

•Write formulas for the following molecular compoundssulfur trioxide

iodine trichloridePhosphorus pentabromide

CI4PCl3OF2