Lesson 10: Types of Chemicals (Objectives 5-7)
Let's continue our examination of types of chemicals by working through examples illustrating Objectives 5-7.
Objective 5 | Objective 6 | Objective 7
Objective 5. From the name of an element, determine the formula (if different from the symbol).
The only elements for which we have to deal with the formula being different from the symbol are the diatomic elements. The diatomic elements are hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine and iodine. Remember, these nonmetals are found across the top of the periodic table, plus the halogens. (You could also remember S8 and P4 and other elements in their families, but the formulas of their molecules can change with conditions, and they are usually represented by their symbols rather than their formulas.) With that information, try your hand at exercise 5.
Exercises
Give the formula for each of the following elements if it is different than the symbol for the element.
a. hydrogen
b. sodium
c. silicon
d. nitrogen
e. oxygen
f. fluorine
g. neon
Answers to Exercises
Give the formula for each of the following elements if it is different than the symbol for the element.
a. hydrogen - The formula is H2.
b. sodium - Sodium does not have a different formula, so we just use the symbol Na.
c. silicon - For silicon, we use the symbol Si.
d. nitrogen - Nitrogen has the formula N2.
e. oxygen - Oxygen has the formula O2.
f. fluorine - Fluorine has the formula F2.
g. neon - For neon we use the symbol Ne.
Objective 6. From the name of a compound, determine whether it is ionic or covalent.
There is more than one step to this process. From the name of the compound, you have to be able to figure out whether you have metal and nonmetal combined with one another, in which case you would have an ionic material, or whether you have only nonmetals, in which case you generally have covalent bonding. There are some exceptions to those generalities. The exceptions involve the polyatomic ion ammonium. Ammonium is a polyatomic cation and contains only nonmetals. So it is possible to have nonmetals that are found in ammonium, nitrogen and hydrogen, in the form of NH4 with a positive charge, combined with anions that are negatively charged and have an ionic compound and still have no metals atoms contained in it. You do have to be aware of that particular exception. In general, however, if you see that the compound contains metal with nonmetal, you have an ionic material and if it has only nonmetals, then you are dealing with a covalent material.
Exercises
Which of the following compounds are ionic and which are covalent?
a. water
b. ammonia
c. sodium oxide
d. potassium nitrate
e. sulfur(VI) oxide
f. manganese(IV) sulfide
g. carbon tetrachloride
Worked-Out Examples (a,b,c)
(a) Water contains hydrogen and oxygen, which are both nonmetals, therefore water is a covalent compound.
(b) Ammonia has the formula NH3. Because ammonia contains nitrogen and hydrogen, which are both nonmetals, it is a covalent material. It has covalent bonding.
Part (c) - sodium oxide contains a metal, sodium, and a nonmetal, oxygen and therefore it would be an ionic material. It would have ionic bonding.
Answers to Exercises
Which of the following compounds are ionic and which are covalent?
a. water - covalent
b. ammonia - covalent
c. sodium oxide - ionic
d. potassium nitrate - ionic
e. sulfur(VI) oxide - covalent
f. manganese(IV) sulfide - ionic
g. carbon tetrachloride - covalent
Objective 7. From the name of a compound, determine whether it is network or molecular.
Again, the guideline for this is dependent on what kind of bonding you have. In a compound, you will either have ionic bonding or covalent bonding. If you have ionic bonding, you will be dealing with a network material. On the other hand, if you have covalent bonding, you will probably have a molecular material. The exceptions, again, are boron, carbon (in the form of graphite and diamond), silicon and silicon dioxide. The only one of these exceptions that is a compound is the silicon dioxide. So if you have silicon dioxide, which is also called quartz, then that would be a network covalent material. Other covalent materials (at least the ones we deal with in this course) will be molecular.
Exercises
Which of the following compounds are network materials and which are molecular materials?
a. carbon dioxide
b. silicon dioxide
c. nitrogen dioxide
d. sodium chloride
e. hydrogen sulfide
f. ferrous bromide
g. water
Worked-Out Examples (f,g)
(f) Ferrous bromide contains iron and bromine, a metal and a nonmetal, so it would have ionic bonding and therefore it would be a network material.
(g) Water contains hydrogen and oxygen, both nonmetals, therefore it has covalent bonding. It is not one of the exceptions that happens to be network covalent, therefore, it will be a molecular covalent material.
Answers to Exercises
Which of the following compounds are network materials and which are molecular materials?
a. carbon dioxide - molecular
b. silicon dioxide - network
c. nitrogen dioxide - molecular
d. sodium chloride - network
e. hydrogen sulfide - molecular
f. ferrous bromide - network
g. water - molecular