9.1 Naming ions and 9.2 Naming and Writing Formulas for Ionic Compounds
In the play Romeo and Juliet William Shakespeare wrote “What’s in a name? That which we call a rose/by any
other name would smell as sweet.” A rose is rosa in spanish, Warda in Arabic, julab in Hindu, 玫瑰 in Chinese and
장미 in Korean. To understand a culture, you must first learn the language used in that culture. Similarly, to
understand chemistry, you must learn its language. Part of learning the language of chemistry involves
understanding how to name ionic compounds.
Monatomic Ions
Ionic compounds are made of a positive metal ion and a negative non-metal ion combined in a
proportion such that their charges add up to zero. Monatomic ions consist of a single atom with a
positive and negative charge resulting from the loss or gain of one or more valence electrons.
Question
In the compound
Calcium Chloride
(CaCl2), what is the
cation?
What is the anion in
calcium Chloride?
Answer
Metals in group 1,2, and 13 tend to lose electrons. When metals in groups 1A, 2A, 13/3A lose electrons
they form cations with positive charges equal to their group number. Non-metals tend to gain electron.
When they gain electrons, they have a negative charge, which makes them an anion. The charge of any
ion in from group 14-18 nonmetals is determined by subtracting 8 from the group number. For example,
Nitrogen has 5 valence electrons. 5-8 = -3 charge.
Determine the charge of the following elements, when they form ions by bonding with another element.
Element
Oxygen
Iodine
Aluminum
Magnesium
Cesium
Ionic charge
To name a cation in a compound made with just an alkali metal, alkaline earth metal or other metal, just
write the name of the element. For the anion, change the ending of the name of the anion to –ide. The
cation is written first. For example, NaBr is sodium bromide.
Name the following ionic compounds:
1. MgCl2 ____________________________
2. CaCl2 ____________________________
3. Na2O ____________________________
4. K3P ____________________________
5. MgS ____________________________
6. SrBr2 ____________________________
7. Al2O3 ____________________________
8. BaO ____________________________
9. BaBr2 ____________________________
10. Li2S ____________________________
11. CoCl ____________________________
12. CoCl2 ____________________________
Transition metals
Transition metals are a little different. The charges of the cations of many transition metal ions must be
determined from the number of electrons donated. Table 9.2 on page 255 shows a table of the metal
ions’ symbols and names. You must first determine the charge of the anion. Then, determine how many
electrons that the transition metal donated. For example, Copper and oxygen combine to form Copper II
oxide. Write a roman numeral of the charge of the transition metal charge. In Copper (II) oxide, the
charge is +2 because there is a roman numeral (II) after copper. We also know that the charge is two
because oxygen accepts two electrons, so if there is one oxygen, it took 2 electrons from copper.
Write the names of the ionic compounds below.
13. Mn2O7 ____________________________
14. Cr2S3 ____________________________
15. CrS3 ____________________________
16. Cu2O ____________________________
17. CuO ____________________________
18. FeO ____________________________
19. Fe2O3 ____________________________
Polyatomic ions
Polyatomic ions are composed of more than one atom. The names of most polyatomic ions end in –ite
or –ate. Polyatomic ions are a tightly bonded group of atoms that behave as a unit and carry a charge.
The charge of the polyatomic ion must be the same as the overall charge of the cations.
Use your reading from before with the polyatomic ions to write the chemical formula of the following
ionic compounds with polyatomic ions.
1.
2.
3.
4.
Chromium (III) nitrite:_______________________
Sodium perchlorate:__________________________
Calcium acetate:_____________________________
Magnesium bicarbonate:________________________________
5.
6.
7.
8.
9.
Sodium Carbonate:_________________________
Sodium phosphate:________________________
Magnesium Sulfate:__________________________
Silver (I) nitrate:___________________________
Sodium Hydroxide:_______________________________
Directions: Here are some more practice problems. Challenge yourself to do more problems.
The transition metals and polyatomic ions are mixed in, so you will have to look on the periodic
table to determine if they have a transition metal or polyatomic ion.
Name the following ionic compounds:
1)
NaBr __________________________________________
2)
CaO __________________________________________
3)
Li2S __________________________________________
4)
MgBr2 __________________________________________
5)
Be(OH)2 __________________________________________
Write the formulas for the following ionic compounds:
6)
potassium iodide __________________________________________
7)
magnesium oxide __________________________________________
8)
aluminum chloride __________________________________________
9)
sodium nitrate __________________________________________
10)
calcium carbonate __________________________________________
11)
lithium sulfate __________________________________________
12)
beryllium phosphide __________________________________________
13)
magnesium hydroxide _________________________________________
14)
sodium phosphate __________________________________________
15)
aluminum carbonate __________________________________________
16)
calcium chloride __________________________________________
17)
sodium cyanide __________________________________________
18)
aluminum oxide __________________________________________
19)
magnesium acetate __________________________________________
20)
ammonium chloride __________________________________________