Writing and Naming Chemical Formulas

Writing and Naming Chemical Formulas

Writing formulas

Steps:

1.       Write the symbols for the ions.

2.       Crisscross the numbers and write them as subscripts.

A.      Binary compounds

It consists of two elements which are formed by metals and non-metals.

                Examples:

·         K⁺   and   Cl^-                    KCl

·         Ca²⁺  and   Br^-                       CaBr₂

·         Mg²⁺ and  N^3-                  Mg³N²

Exercises:

Write the formula for the following:

1.       Strontium fluoride

2.       Calcium sulfide

3.       Calcium phosphate

Naming Formulas

1.       In naming binary compounds containing metals with fixed oxidation number,  the metal is named first, followed by the nonmetal with the ending –ide.

               Example:

              Ca₃N_{2  -}  calcium nitride

             Exercises:

1.        CaBr₂                              4. KCl

2.       Mg₃N₂                              5. Na₂O

3.       Al₂S₃

2.       In naming binary compounds containing metals with variable oxidation numbers, the oxidation number must be specified.

Two types of naming system:

1.       Stock system – the oxidation number is indicated by Roman numeral in parentheses.

2.       Classical system – the suffixes –ous and -ic are used to denote the lower and higher oxidation states. 

Cu²⁺ O^2-     Cu₂O

                      Copper (I) oxide

                      Cuprous oxide

                Exercises:

1.       Fe²⁺   and  Cl^-                     4. Pb²⁺   and   I^-

2.       Sn⁴⁺   and   F^-                      5. Hg²⁺  and   Br^-

3.       Cu²⁺  and O^2-

B.      Binary compounds containing two non-metals

Prefixes are used

CO – carbon monoxide

CO₂ – carbon dioxide

Exercises:

1.       Name the following compounds

1.       NO                         4. P₂O₅

2.       SO₂                        5. PCl₅

3.       CCl₄

2.       Write the chemical formulas of the following:

1.       Nitrogen dioxide                        4. sulfur trioxide  

2.       Dinitrogen trioxide                    5. Diphosphorus pentoxide

3.       Carbon disulfide

C.      Metals with Polyatomic Ions

·         Polyatomic ion is a stable group of atoms that carries an overall electrical charge.

·         Parentheses are placed around the polyatomic ion and subscript is written just after the close parenthesis whenever a multiple polyatomic ion is necessary.

                 Mg²⁺ OH^-      Mg(OH)₂

·          Parentheses are not used when single polyatomic ion is present.

                                KKClO₃                  CaCO₃                 NaHCO₃

  Exercises:

                   Write the correct formula for

1.       Strontium bicarbonate                     4. Magnesium phosphate

2.       Ammonium nitrate                           5. Copper (III) carbonate

3.       Iron (III) sulfate

Give the name of the following:

1.       K₂CrO₄                                               4. FeSO₄

2.       Zn(NO₃)₂                                             5. Sn(OH)₄

3.       CuClO₃

D.      Acids

1.       Binary

Hydrogen and a Nonmetal

·         The word hydrogen comes first; then the second word is made by affixing the

suffix  –ide to the root word of the nonmetal.

HCl   hydrogen chloride

·         When these substances are dissolved in water, they become aqueous acids. The prefix hydro is attached to the root word of the nonmetal and the suffix –ic is added. The word acid becomes the last term.

H₂S (aq)     hydrosulfuric acid

HCl (aq)    hydrochloric acid

2.       Tertiary/ ternary/ oxyacids

·         -ite – ous acid     phosphorous acid (H₃PO₃)

·         -ate – ic acid       Sulfuric acid (H₂SO₄)

E.       Bases –(OH)

Fe(OH)₂  - ferrous hydroxide

Mn(OH)₃ – manganic hydroxide

Sn(OH)₂ – Tin (II) hydroxide