1. Writing Formulas and Naming Compounds
Section 3
Writing Formulas and Naming Compounds

2. Essential Questions How are oxidation numbers determined?
How are formulas for ionic and covalent compounds written?
How are ionic and covalent compounds named?

3. Review Vocabulary
ion: an atom that has gained or lost electrons

4. New Vocabulary
oxidation number
binary compound
polyatomic ion
hydrate

5. Writing Chemical Formulas
To write a chemical formula, you need to know the elements involved and the number of electrons they gain, lose, or share to become stable. This last piece of information is what chemists refer to as an element’s oxidation number. An oxidation number is a positive or negative number that indicates how many electrons an atom has gained, lost, or shared to become stable.
©Bettmann/Corbis

6. Look at Pg.566 Figure 17: You are familiar with these oxidation number for the A-Team.
II. The B- Team elements can have more than one oxidation number. Some common ones are in Table 2 at the bottom of the page.
III. Binary Compounds are the easiest ones to name. We use the steps on Pg.567 to do this.
Let do the practice problems at bottom of this page:

7. Compounds With Complex Ions
Not all compounds are binary. Many common compounds contain more than two atoms. Baking soda—used in cooking, as a medicine, and for brushing your teeth—has the formula NaHCO3. This is an example of an ionic compound that is not binary. Some compounds, including baking soda, contain polyatomic ions. The prefix poly– means “many,” so the term polyatomic means “having many atoms.” A polyatomic ion is a positively or negatively charged, covalently bonded group of atoms. Polyatomic ions as a whole contain two or more elements. Even though polyatomic ions contain more than one element, they act like individual ions in forming compounds. The polyatomic ion in baking soda is the hydrogen carbonate ion (HCO3–), which is commonly called bicarbonate.

8. Lets name the following compounds:
NH4Cl
LiC2H3O2
Ca CO3
Mg3(PO4)2

9. Naming Binary Covalent Compounds
Covalent compounds are those formed between elements that are nonmetals. Some pairs of nonmetals can form more than one compound with each other. For example, nitrogen and oxygen can combine to form a number of different compounds, including N2O, NO, NO2 , and N2O5 . In the system of naming using oxidation numbers that you have just learned, each of these compounds would be called nitrogen oxide. From that name, you would not know the composition of the compound. So, a different system of naming must be used for covalent compounds.

10. Now we can write molecular formulas: Let practice. I have a handout
Now we can write molecular formulas: Let practice. I have a handout. We will do this on the board and you on your paper.

11. Compounds with Added Water
Some compounds have water molecules as part of their structures. These compounds are called hydrates. A hydrate is a compound that has water chemically attached to its atoms and written into its chemical formula.
Giovanni Guarino/age fotostock

12. Assessment 1. Which is a binary ionic compound? O2 NaF H2SO 4 Cu(NO3)2
CORRECT
H2SO 4 C
Cu(NO3)2 D

13. Assessment 2. Which of these is an example of an anhydrous compound?
CaSO4 B
CORRECT
CuSO4 · 5H2O C
CaSO4 · 2H2O D

14. Assessment 3.
Which of the following is an atom that has gained an electron?
negative ion A
CORRECT
positive ion B
polar molecule C
nonpolar molecule D