Chemistry Reference
In-Depth Information
One clear example of this can be found on your kitchen table. Elemen-
tal chlorine is a yellowish-green poisonous gas that was used as a weapon
in World War I. Elemental sodium is a highly reactive metal, which will
react violently with water, often with explosive results. When these two
potential deadly elements are combined in a chemical reaction, you get
sodium chloride or table salt, which you can put on your French fries and
safely eat. You see, elements that combine chemically to form a compound
lose their individual properties in the chemical reaction. The new substance
will have its own unique properties. See the reaction that follows.
Sodium and chlorine are elements, and they react to form sodium chlo-
ride, which is a compound. The reaction in Figure 1-1b shows that two
parts of the monatomic element so-
dium will react with one part of the di-
atomic element chlorine to form two
parts of sodium chloride. Notice that
diatomic chlorine is represented as Cl
2
,
whereas monatomic sodium is repre-
sented as Na, without a subscript. Chlo-
rine does not get a subscript when it is
part of the compound, NaCl, because
when we say that an element is di-
atomic, we mean in its elemental form.
You can also look at Figure 1-1b
and realize that, unlike elements, compounds can be decomposed into sim-
pler substances by ordinary chemical means. Following this paragraph is
the reverse reaction for the decomposition of the compound sodium chlo-
ride into its constituent elements, sodium and chlorine.
2NaCl
(s)
2Na
(s)
+ Cl
2(g)
sodium chloride yields sodium + chlorine
Do you know what the subscript “(s)” and “(g)” represent in the equa-
tion? They indicate the phase in which the substance in question is found
in. The sodium and the sodium chloride are found in a solid phase, as rep-
resented by the “(s)” subscript. The chlorine is followed by a “(g),” be-
cause it is found in a gas phase. If any of the substances were found in the
liquid phase, they would be followed by a subscript “(l).”
Other examples of compounds, which are chemical combinations of
two or more elements, include water (H
2
O), carbon dioxide (CO
2
), and
glucose (C
6
H
12
O
6
). Compounds that are only made up of two elements,
2Na
(s)
+ Cl
2(g)
2NaCl
(s)
Two atoms of monatomic sodium
react with one molecule of
diatomic chlorine to form two
formula units of sodium chloride.
Figure 1-1b
