OUTLINE
2-1 Atoms and Molecules
2-2 Chemical Formulas
2-3 Ions and Ionic Compounds
2-4 Names and Formulas of Some
Ionic Compounds
2-5 Atomic Weights
2-6 The Mole
2-7 Formula Weights, Molecular
Weights, and Moles2-8 Percent Composition and
Formulas of Compounds
2-9 Derivation of Formulas from
Elemental Composition
2-10 Determination of Molecular
Formulas
2-11 Some Other Interpretations of
Chemical Formulas
2-12 Purity of SamplesT
OBJECTIVES
After you have studied this chapter, you should be able to- Understand some early concepts of atoms
- Use chemical formulas to solve various kinds of chemical problems
- Relate names to formulas and charges of simple ions
- Combine simple ions to write formulas and names of some ionic compounds
- Recognize and use formula weights and mole relationships
- Interconvert masses, moles, and formulas
- Determine percent compositions in compounds
- Determine formulas from composition
- Perform calculations of purity of substances
T
he language we use to describe the forms of matter and the changes in its com-
position is not limited to use in chemistry courses; it appears throughout the
scientific world. Chemical symbols, formulas, and equations are used in such
diverse areas as agriculture, home economics, engineering, geology, physics, biology,
medicine, and dentistry. In this chapter we describe the simplest atomic theory. We shall
use it as we represent the chemical formulas of elements and compounds. Later, after
additional facts have been introduced, this theory will be expanded.
The word “stoichiometry” is derived from the Greek stoicheion,which means “first
principle or element,” and metron,which means “measure.” Stoichiometrydescribes the
quantitative relationships among elements in compounds (composition stoichiometry) and
among substances as they undergo chemical changes (reaction stoichiometry). In this chap-
ter we are concerned with chemical formulas and composition stoichiometry. In Chapter
3 we shall discuss chemical equations and reaction stoichiometry.
It is important to learn this
fundamental material well so that you
can use it correctly and effectively.Some minerals and gems, left to
right: Galena, PbS; aquamarine,
Be 3 AlSi 6 O 18 (colored by trace
amounts of iron); ruby, Al 2 O 3 (with
some Cr^3 ions replacing Al^3
ions); sulfur, S 8 ; silver, Ag; elbaite,
Na(Li,Al) 3 Al 6 Si 6 O 18 (BO 3 ) 3 (OH) 4
(the notation [Li,Al] indicates a
variable ratio of lithium and
aluminum among elbaite samples);
sapphire, Al 2 O 3 (with various
colors due to different metal ions
substituting for Al^3 ions);
fluorite, CaF 2 ; copper, Cu; azurite,
Cu 3 (CO 3 ) 2 (OH) 2 ; and malachite,
Cu 2 CO 3 (OH) 2.