a chemical reaction occurs when a sodium atom is combined with a chlorine
atom; the property of the resulting chemical compound is table salt. If the
sodium chloride (table salt) compound were broken down into its chemical ele-
ments, you would see that the atoms of sodium and chlorine remain unchanged.
Theoretically a chemical reaction can be reversed if the conditions are opti-
mal. A chemical reaction that is reversible is called a reversible reaction. (see
Fig. 2-6)
In practical use, same reactions can do this much easier than others. Some of
these reversible reactions occur due to the instability of the reactants and prod-
ucts, while others will only reverse under special conditions. Examples of spe-
cial conditions could be the presence of water or the application of heat.
CHAPTER 2 Chemical Elements of Microorganisms^33
Notation Description
Na+ The plus superscript indicates a positive ion.
Cl− The negative superscript indicates a negative ion.
Na++Cl−→NaCl The plus sign indicates synthesizing (combining) two
particles. The right arrow indicates that a chemical
reaction occurs towards the product.
NaCl →Na++Cl− Decomposing (breaking up) a molecule or chemical
compound.
NaOH +HCl →NaCl +H 2 O Exchange reaction where a chemical compound is de-
composed into its chemical elements and those chemi-
cal elements are synthesized into a new compound.
Here, sodium hydroxide (NaOH) and hydrochloric acid
(HCl) form salt (NaCL) and water (H 2 O).
Na++ Cl−←→NaCl Reversible reaction is noted with a right arrow over a
left arrow.
C – C Single covalent bond.
C = C Double covalent bond.
C ≡ CTriple covalent bond.
H 2 OAsubscript following a chemical symbol indicates the
number of atoms (two hydrogen atoms). If no subscript
is used, then it is implied there is one atom (here, one
oxygen atom).Table 2-2. Commonly Used Chemical Notations