Naming Compounds and Molecules

• The FIRST thing you must do is decide if the compound is IONIC or COVALENT.

• Why? Each type of compound is named differently!

If it is Covalent…

• Follow the prefix method

• Affix the following prefixes to each element indicating how many there are.

• One Mono-• Two Di-• Three Tri-• Four Tetra-• Five Penta-• Six Hexa-• Seven Hepta-• Eight Octa-• Nine Nona-• Ten Deca-

Other Covalent Rules

• Name the element farther left on the periodic table first.

• If the first element only has one atom, the “mono-” is dropped.

• On the last word, the suffix is dropped and the ending –ide is added.

Covalent Examples

• CO2

• There is only one carbon, so the “mono-” is dropped.

• There are two oxygen atoms = DiCarbon Dioxide

• CO• There is only one carbon, so the “mono-” is

dropped. • There is one oxygen atom = mono

Carbon Monoxide

A few more Covalent Examples

• Tetracarbon Difluoride• There are four carbon atoms • There are two fluorine atoms

C4F2

• Dihydrogen Monoxide• There are two hydrogens • There is one oxygen

H2O

That was easy, Right?

Let’s try ionic compounds…

If it is Ionic…• Ionic compounds DO NOT have

prefixes.

• Example: Write the formula for Aluminum Fluoride

• How do you do it???

• Let’s think about it practically, first.

• How? Draw the Bohr model for each and figure out how many of each atom are needed.

Another Way to Think about It…• Aluminum needs to give 3 electrons away.

• Fluorine only needs one electron

• You need 3 fluorines to take all of aluminum’s electrons

AlF3

That Seems Like A lot of work. Is There Another Way to Think About

It???• YES!!!

• Step 1: Determine the Charge of the ion.–How? What would its charge be if

its outer energy level were full?–First, write the element’s symbol

and then its charge as a superscript–Example: Aluminum Fluoride

Aluminum• How many valence electrons does Aluminum

have?3

• What will Aluminum do with these?

Give them away.

13+ (protons)10- (electrons)

3+ (total charge)

Al+3

What about Fluorine?• How many valence electrons does fluorine have?

7• What does fluorine need to be like a noble gas?

One more electron

9+ (protons)

10- (electrons)

-1 (total charge)

F-1

• A positive ion is called a CATION.

• A negative ion is called an ANION.

• The metal is always listed first, the nonmetal second.

• The ending of the nonmetal is dropped and the ending –ide is added.

Now What?

• Step 2: Write each symbol and charge– write the metal first, the nonmetal second

Al F

• Step 3: Follow the Criss-Cross Rule– Aluminum’s charge becomes fluorine's subscript

and vice versa– The charge symbols are dropped (the + or -)

+3 -1

Final Formula

AlF3

Another Example: Sodium Oxide

• Step 1: Find the charges of the ions• Sodium has 1 valence electron• It gives the electron away• Charge is +1• Oxygen has 6 valence electrons• It needs two more electrons• Charge is –2

Na+1 O-2

Step 2: Write each symbol and charge

Na O

Step 3: Follow the Criss-Cross Rule

+1 -2

Final Formula for Sodium Oxide

Na2O

Another Way to Think About It: Using Lewis Dot Structures

• Draw the Lewis Dot for each element

• Sodium only has one electron to give.

• In order for oxygen to be like a noble gas, there must be two sodiums.

Na ONa

Na2O

Name the Following Ionic Compounds

• BaBr

• Remember, NO PREFIXES NEEDED!!

• Barium Bromide

• K3P

• Potassium Phosphide

• Rb2S

• Rubidium Sulfide

Transition Metals• Transition metals can often make more than

one ion. • The ion charge is written as a ROMAN

NUMERAL after the metal• The charges of metals are ALWAYS

positive.• Examples:

– Iron (III) Fe+3

– Copper (II) Cu+2

• Remember, when naming ionic compounds, if it is a transition metal, to include the roman numeral!

Example with a Transition Metal• Copper (II) Chloride

• Step 1: Find the charges of the ions

• We already know copper’s charge from the roman numeral (remember, metals always have a POSITIVE charge)

Cu+2

• Chlorine has 7 valence electrons

• Chlorine needs 1 electron

• Charge is –1

Cl-1

Step 2: Write the Symbols & Charges

Cu Cl

Step 3: Follow the Criss-Cross Rule

+2 -1

Final Formula for Copper (II) Chloride:

CuCl2

Another way to Think About it Using Lewis Dot Structures

• First, draw the Lewis Dot for each element.

• Copper gives away two electrons

• Chlorine needs one electron

• It takes 2 chlorines to take all of copper’s electrons.

CuCl

Cl

Final Answer: CuCl2

If it is Polyatomic…• You will recognize a polyatomic (in most cases) by

the ending of the last word in the name.• Many polyatomics DO NOT end in –ide• Examples: Sulfate, Nitrite, Carbonate• Examples that end in –ide: Hydroxide, Cyanide• Polyatomics already give you the charge of the ion

(just look it up on a chart)• Write the metal first, the polyatomic second, then

follow the rules of ionic bonding.• If more than one polyatomic is needed, put the entire

polyatomic in parentheses and put the subscript outside the parentheses.

Polyatomic Example

• Lithium Sulfate

• Step 1: Find the charges of the ions

• Lithium has 1 valence electron.

• Lithium gives the electron away = +1 charge

Li+1

• Sulfate…look it up on a chart

SO4-2

Step 2: Write the Symbols & Charges

Li SO4

Step 3: Follow the Criss-Cross Rule

+1 -2

Final Formula for Lithium Sulfate

Li2(SO4)1

OK, time for more practice.

See the practice sheet….