Nomenclature (naming & formulas of compounds).

The general procedure for naming and writing molecular formulas is:

First: Recognize the type of compound (the type dictates the rules-ionic or covalent.

Do not skip this step ever!

An ion is a charged atom or molecule produced by the addition or removal of electrons. The ion has a non-zero net charge, which must be included when writing a stand-alone ion.

Cation: positive charge, formed by species losing negatively charged e-

Anion: negative charge, formed by species gaining negatively charged e-

While stand-alone ions are charged, ionic compounds are neutral; i.e., the net charge is zero. This information enables you to write the chemical formula, given the ions.

Rules for naming and writing chemical formulas

I. Recognition of compound type. DO NOT SKIP THIS STEP EVER!

A. General strategy.  Look at the name or chemical formula:

1. Is the cation a metal?

• If YES → the compound is ionic.

B. Recognize the type of compound (cation is metal = ionic), then apply the appropriate system of naming.

1. If the cation is a metal, the compound is ionic and uses this system of ionic compound naming.

2. If the cation is not metal, use the system of naming covalent compounds.

C. In the formula (and the name):  cation first, anion second (ALWAYS this order)

2. If NO → the compound should only be nonmetals/metalloids, and it is covalent.

D. EXAMPLE:  CaO

1. Recognize type:  metal - nonmetal (ionic)

2. Identify.            cation:  Ca²⁺                        anion:   O^2-

3. Name ions. Metal is Grp II, no Roman numeral.             

calcium                              oxygen= oxide

4. Name compound:         calcium oxide

If variable charges for metal (transition), Roman numeral tells you the charge.

E. Procedure (name → formula)

1. Recognize the type.

2. Identify the cation & anion (and charges).

3. Write the ions (with charges).

4. Are charges are equal & opposite?  Otherwise, calculate how many of each ion are required to give net charge = 0.

F. EXAMPLE:  manganese(IV) oxide

1. Recognize type:  metal cation (ionic)

2. Identify: cation:  manganese(IV)    anion:  oxide

3. Write ions (with charges): Mn⁴⁺                       O^-2

4. Apply subscripts:  Need to combine 1 Mn⁴⁺and 2 O^-2to give a net charge of zero:  MnO₂

G. Polyatomic Ions

1. Find the ions listed on table 4.4 names, formulas, & charges. This table is given in the test.

2. Identify: cation: anion: 

3. Write ions (with charges):                        

4. Apply subscripts:

Example:  Calcium phosphate

5. Identify: Cation: Calcium: group 2 : Ca²⁺. no Roman numeral.

anion :PO₄^-3From table 4.4

Write ions (with charges): Ca²⁺                         PO₄^-3

Apply subscripts:  Need to combine 3 Ca²⁺and 2 PO₄^-3 to give a net charge of zero:  Ca₃ (PO₄)₂

5. Covalent compounds.

H. Procedure (formula → name)

1. First element =element name

2. Second element = stem name +   -ide

3. From each subscript (denoting # of those atoms in molecule), add correspondingprefix to each element

i. Note that "mono" is not usually used unless more than one binary compound can be formed between those two elements.

ii. Example:  CO (carbon monoxide); CO₂ (carbon dioxide)

I. EXAMPLE:  N₂O₅

1. First element:  nitrogen

2. second element:  oxygen = oxide

3. Add prefixes:  dinitrogen (from subscript 2)                      

4. pent(a)oxide  (from subscript 5)

5. Name:  dinitrogen pentoxide

DO NOT use prefix system with ionic compounds! This is a common mistake...be careful! For example, CaCl₂ is NOT calcium dichloride (it is calcium chloride). How do you know? The first step in naming is to recognize the type of compound-ionic, covalent. Then apply the rules. CaCl₂ is metal-nonmetal, thus, an ionic compound, and ionic compounds never use prefixes.  Be aware that if there is already a prefix as part of the polyatomic ion (e.g., dichromate), then you must retain the prefix. Just don't add prefixes to ionic compounds.

Name the following compounds (be sure to include prefixes and roman numerals WHEN necessary): Hint: Decide Ionic or Covalent fist