Naming and Writing Formulas for Compounds

Chemistry                                                                         Guided Instructional Activity 4-1
Unit: Chemical Compounds and Reactions                                            Reading: Chapter 7

Working Mode: Pairs. Follow the instructions below, answer the questions on a piece of paper.  Each student should prepare his/her own sheet.

Learning Objectives:  To name compounds and acids from their formulas and write their formulas from the names.

PART 1: Ionic Compounds

Writing formulas from names:  e.g.  nickel (III) nitrate

Step 1: Write the ionic symbol of the cation and anion.     Ni³⁺  NO₃^-
            (For cations with more than one charge, the charge will be given as a roman
numeral.)

Step 2: Use the “criss-cross” method to determine the subscripts of each of the ion in the formula.   Ni ₍₁₎ NO_{3 (3)}  

(The criss-cross method helps one find the least common multiple of the charges.  An ionic compound formula is the least whole number ratio of ions in which the total positive charge equals the total negative charge of the cations and anions respectively.)

Step 3: Write the empirical formula (least whole number ratio of ions of the compound).  Ni(NO₃)₃ 

(Parentheses are used around polyatomic ions when more than one of the ion is required in the formula. 

Write the formulas for the following ionic compounds:

a.       silver sulfide

b.      tin(IV) sulfate

c.       potassium permanganate

d.      titanium (IV) oxide

e.       aluminum chloride

f.        indium selenide

Writing the name of ionic compounds from the formula:  e.g.  Fe₂(CO₃)₃

Step 1: Name the cation.  “iron (III)”

            (For cations with more than one charge, the charge needs to be included as a

roman numeral.  The charge is deduced from the subscripts of the ions in the

empirical formula, i.e. the reverse “criss-cross” method.)

Step 2: Name the anion.  “carbonate” 

(Polyatomic ions have names that the student has memorized.  Monoatomic anions end with the “-IDE” suffix.)

Step 3: Put the two names together:  “iron (III) carbonate” 

Name the following ionic compounds

1. Ba(ClO)₂
2. KBr
3. ZnSO₄
4. NH₄Cl
5. AuCl₃
6. Hg₂S
7. Li₃PO₃
   
    

PART 2: Covalent (or molecular) Compounds (binary only)

Writing formulas from names:  e.g.  dinitrogen monoxide

Step 1: Write the elemental symbols of the two elements:  N  O

Step 2: Make the greek prefix the element’s subscript   N₂O  

(Subscripts of “1” are never written.)

Write the formulas of the following molecular compound names:

a.       phosphorus pentabromide

b.      silicon tetrafluoride

c.       dicarbon disulfide

d.      nitrogen triiodide

e.       sulfur hexafluoride

f.        tetraarsenic decaoxide

Writing names from molecular formulas:  e.g.  CS₂

Step 1: Write the name of the first element as on the periodic table.     “carbon”

Step 2: Add a Greek prefix to this name if there is more than one of the element in the compound.

Step 3: Write the name of the second element ending with the “-IDE” suffix.  Always add a Greek prefix to indicate the number of the second element.

Write the names of the following molecules:

a.       NO₂

b.      N₂O₄

c.       P₂S₅

d.      BF₃

e.       P₄O₁₀

PART 3: Acids

Writing formulas from names and vice versa:  e.g. “HBr”  and “sulfuric acid”

Follow the guidelines for the relationship of the acid name to the non-hydrogen anion portion.

binary acids (acids with only two different elements):  “hydro _____-ic acid”

            (OR when anion portion ends with “-IDE”)

ternary acids (acids with polyatomic anions):

      “_________-ic acid”, when the polyatomic anion portion ends with “-ATE”

       “_________-ous acid”, when the polyatomic anion portion ends with “-ITE”

Step 1: Formulas to names: Identify the anion portion and name the acid accordingly.  

                        HBr – “Br” is bromIDE  à  “hydrobromic acid”

Step 2: Names to formulas: Determine the anion based on the above pattern and add an “H” per negative charge. (Assume that hydrogen, H, has a +1 charge in the compound, even though acids are usually made of non-metals, and therefore covalent.)

            sulfur-ic acid  à sulfate ion;  2 H⁺  +  SO₄^2-  à  H₂SO₄

Give the formula or name for the following acids:

a.       HF

b.      HClO₃

c.       H₃PO₃

d.      HC₂H₃O₂

e.       nitric acid

f.        hydrochloric acid

g.       perchloric acid

h.       sulfurous acid

1.                  ammonium sulfate

2.                  disulfur dichloride

3.                  lead (IV) oxide

4.                  hydroiodic acid

5.                  copper (II) cyanide

6.                  oxygen difluoride

7.                  scandium nitrite

8.                  chromic acid

9.                  aluminum chromate

10.              acetic acid

11.              arsenic pentachloride

12.              rubidium bicarbonate

13.              HgF₂

14.              Co(MnO₄)₂

15.              CdCO₃

16.              NF₃

17.              HNO₃

18.              HCl

19.              SnCO₃

20.              N₂O₂

21.              HBr

22.              BrF₇

23.              P₄O₆

24.              AgCN