The Foundations of Chemistry

In modern terminology, O 2 is named dioxygen, H 2 is dihydrogen, P 4 is tetraphospho-

rus, and so on. Even though such terminology is officially preferred, it has not yet gained

wide acceptance. Most chemists still refer to O 2 as oxygen, H 2 as hydrogen, P 4 as phos-

phorus, and so on.

Molecules of compounds are composed of more than one kind of atom. A water mol-

ecule consists of two atoms of hydrogen and one atom of oxygen. A molecule of methane

consists of one carbon atom and four hydrogen atoms. The shapes of a few molecules are

shown in Figure 2-4.

Atoms are the components of molecules, and molecules are the stable forms of many

elements and compounds. We are able to study samples of compounds and elements that

consist of large numbers of atoms and molecules. With the scanning tunnelling micro-

scope it is now possible to “see” atoms (Figure 2-5). It would take millions of atoms to

make a row as long as the diameter of the period at the end of this sentence.

Methane is the principal component of
natural gas.

50 CHAPTER 2: Chemical Formulas and Composition Stoichiometry

P

P

P P

(a)

S S S S

SS S

S

(c)

S S

S

S S

S S

S

(b)

Figure 2-3 (a) A model of the P 4 molecule of white phosphorus. (b) A model of the S 8

ring found in rhombic sulfur. (c) Top view of the S 8 ring in rhombic sulfur.

Figure 2-4 Formulas and models for molecules of some compounds.

H 2 O

(water)

CO 2

(carbon dioxide)

CH 4

(methane)

C 2 H 5 OH

(ethyl alcohol)