From Wikipedia, the free encyclopedia
Chemical formula of a unit of an ionic compound or covalent network solid
In
chemistry
, a
formula unit
is the smallest unit of a non-molecular substance, such as an
ionic compound
,
covalent network solid
, or
metal
.
[1]
[2]
It can also refer to the
chemical formula
for that unit. Those structures do not consist of discrete molecules, and so for them, the term formula unit is used. In contrast, the terms
molecule
or molecular formula are applied to molecules.
[3]
The formula unit is used as an independent entity for
stoichiometric
calculations.
[4]
[5]
Examples of formula units, include ionic compounds such as
NaCl
and
K
2
O
and covalent networks such as
SiO
2
and
C
(as
diamond
or
graphite
).
[6]
In most cases the formula representing a formula unit will also be an empirical formula, such as
calcium carbonate
(
CaCO
3
) or
sodium chloride
(
NaCl
), but it is not always the case. For example, the ionic compounds
potassium persulfate
(
K
2
S
2
O
8
),
mercury(I) nitrate
Hg
2
(NO
3
)
2
, and
sodium peroxide
Na
2
O
2
, have empirical formulas of
KSO
4
,
HgNO
3
, and
NaO
, respectively, being presented in the simplest whole number ratios.
[7]
In
mineralogy
, as minerals are almost exclusively either ionic or network solids, the formula unit is used. The number of formula units (Z) and the dimensions of the
crystallographic
axes are used in defining the
unit cell
.
[8]
References
[
edit
]
- ^
Peter Atkins, Julio de Paula, Ronald Friedman, Physical Chemistry: Quanta, Matter, and Change, 2nd Edition
- ^
"Does the term Formula Unit apply to giant covalent networks composed of one type of atom, like Diamond or Graphene which have formula C?"
.
- ^
"Chapter 4 ? Covalent Bonds and Molecular Compounds"
.
wou.edu
. Retrieved
2023-10-08
.
- ^
"Formula Units vs Empirical Formula - CHEMISTRY COMMUNITY"
.
lavelle.chem.ucla.edu
. Retrieved
2023-09-10
.
- ^
"2.2: Chemical Formulas"
.
Chemistry LibreTexts
. 2015-01-27
. Retrieved
2023-09-10
.
- ^
Steven S. Zumdahl; Susan A. Zumdahl (2000),
Chemistry
(5 ed.), Houghton Mifflin, pp. 470-6,
ISBN
0-618-03591-5
- ^
"Is Formula Unit usually an empirical formula but not always? - Chemical Forums"
.
chemicalforums.com
. Retrieved
2023-10-06
.
- ^
Smyth, Joseph R. and Tamsin C. McCormick, 1995,
Crystallographic Data for Minerals,
American Geophysical Union
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