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What is the meaning of the dot notation in chemical formulas?
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Ooi Teng He
What is the meaning of the dot notation in chemical formulas?
Let's mention a formal definition for this notation from the IUPAC Nomenclature of Inorganic chemistry Recommendations (Red Book 2005) (external links added):
IR-2 GRAMMAR
IR-2.5 DOTS, COLONS, COMMAS AND SEMICOLONS
(…)
(c) Centre dots in formulae of (formal) addition compounds, including hydrates, adducts,
clathrates, double salts and double oxides, separate the individual constituents. The dot is
written in the centre of the line to distinguish it from a full stop (period).
Examples:
$\ce{BF3.NH3}$
$\ce{ZrCl2O.8H2O}$
$\ce{CuCl2.3Cu(OH)2}$
$\ce{Ta2O5.4WO3}$
(Please note that according to the original text typography, there should be no whitespace around the dot and around the following numeral – stoichiometric coefficient; here it comes (if it does) from the chemical formatting script, which is not 100% perfect)
Let's mention a formal definition for this notation from the IUPAC Nomenclature of Inorganic chemistry Recommendations (Red Book 2005) (external links added):
IR-2 GRAMMAR
IR-2.5 DOTS, COLONS, COMMAS AND SEMICOLONS
(…)
(c) Centre dots in formulae of (formal) addition compounds, including hydrates, adducts, clathrates, double salts and double oxides, separate the individual constituents. The dot is written in the centre of the line to distinguish it from a full stop (period).
Examples:
$\ce{BF3.NH3}$
$\ce{ZrCl2O.8H2O}$
$\ce{CuCl2.3Cu(OH)2}$
$\ce{Ta2O5.4WO3}$
(Please note that according to the original text typography, there should be no whitespace around the dot and around the following numeral – stoichiometric coefficient; here it comes (if it does) from the chemical formatting script, which is not 100% perfect)
Let's take the example of copper sulfate penta-hydrate: $\ce{CuSO4. 5H2O}$. The dot here is used essentially as an expression of
ignorance to indicate that, though the parts of the
molecule separated by the dot are bonded to one another in some fashion, the exact structural details of that interaction are not fully expressed in the resulting
formula.
Using Alfred Werner’s coordination
theory that indicates
that four of the five water molecules are actually
bonded directly to the $\ce{Cu}$ in the form of a complex
aquo ion $\ce{[Cu(H2O)4]^2+}$, then the formula is better
expressed
as $\ce{[Cu(H2O)4][SO4].H2O}$
So, the dot here signifies ignorance of how the
subunits of a formula are structurally related.
The use of dots in phase diagrams
Let's take the example of the ternary phase diagram of $\ce{Na2O}$,$\ce{Al2O3}$,$\ce{SiO2}$. The formulas of
the various resulting complex sodium aluminosilicates
are all expressed in the form $\ce{a Na2O.b Al2O3.c SiO2}$
in which it is implicitly understood that these initial starting components do not exist as such within the resulting compounds. They represent the combining ratios of the binary/ternary starting materials required for the synthesis of the compound.
Let's take the example of copper sulfate penta-hydrate: $\ce{CuSO4. 5H2O}$. The dot here is used essentially as an expression ofignorance to indicate that, though the parts of themolecule separated by the dot are bonded to one another in some fashion, the exact structural details of that interaction are not fully expressed in the resultingformula.
Using Alfred Werner’s coordinationtheory that indicatesthat four of the five water molecules are actuallybonded directly to the $\ce{Cu}$ in the form of a complexaquo ion $\ce{[Cu(H2O)4]^2+}$, then the formula is betterexpressedas $\ce{[Cu(H2O)4][SO4].H2O}$
So, the dot here signifies ignorance of how thesubunits of a formula are structurally related.
The use of dots in phase diagrams
Let's take the example of the ternary phase diagram of $\ce{Na2O}$,$\ce{Al2O3}$,$\ce{SiO2}$. The formulas ofthe various resulting complex sodium aluminosilicatesare all expressed in the form $\ce{a Na2O.b Al2O3.c SiO2}$ in which it is implicitly understood that these initial starting components do not exist as such within the resulting compounds. They represent the combining ratios of the binary/ternary starting materials required for the synthesis of the compound.
By writing $\ce{AB.xCD}$ chemists mean that there are CDs are found in the crystalline framework of AB. The most common example of this is water trapped inside the crystal structure of ionic compounds. (See water of crystallization in wikipedia)
An example that's often taught is $\ce{CuSO4.5H2O}$. See that 5 that's a representative of $x$? It means that water can be bound only with intermolecular interactions, but it exists in the structure in a stoichiometric ratio.
In summary, when a dot is used to break a formula into subunits, it may signify ignorance of how the subunits are structurally related, as in our inorganic example; or it may correspond to actual significant structural subunits, as in our organic example; or it may represent the combining ratios of the binary starting materials required for the synthesis of the compound, as in our phase diagram example.
As a result, for example in direct addition reactions, where there is ignorance about the structural relation of the compounds, we use a dot.
By writing $\ce{AB.xCD}$ chemists mean that there are CDs are found in the crystalline framework of AB. The most common example of this is water trapped inside the crystal structure of ionic compounds. (See water of crystallization in wikipedia)
An example that's often taught is $\ce{CuSO4.5H2O}$. See that 5 that's a representative of $x$? It means that water can be bound only with intermolecular interactions, but it exists in the structure in a stoichiometric ratio.
In summary, when a dot is used to break a formula into subunits, it may signify ignorance of how the subunits are structurally related, as in our inorganic example; or it may correspond to actual significant structural subunits, as in our organic example; or it may represent the combining ratios of the binary starting materials required for the synthesis of the compound, as in our phase diagram example.
As a result, for example in direct addition reactions, where there is ignorance about the structural relation of the compounds, we use a dot.
@Apurva copper(II) sulfate pentahydrate is a crystalline solid. Water does not form a separate phase, and its molecules are trapped inside the gaps in the crystal. If you heat it, the lost water would then be water vapor (with a white $\ce{CuSO4}$ powder), but nothing of the sort can be said before it happens.More
Let's mention a formal definition for this notation from the IUPAC Nomenclature of Inorganic chemistry Recommendations (Red Book 2005) (external links added):
(Please note that according to the original text typography, there should be no whitespace around the dot and around the following numeral – stoichiometric coefficient; here it comes (if it does) from the chemical formatting script, which is not 100% perfect)
Let's mention a formal definition for this notation from the IUPAC Nomenclature of Inorganic chemistry Recommendations (Red Book 2005) (external links added):
(Please note that according to the original text typography, there should be no whitespace around the dot and around the following numeral – stoichiometric coefficient; here it comes (if it does) from the chemical formatting script, which is not 100% perfect)
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The use of dots in inorganic chemistry
Let's take the example of copper sulfate penta-hydrate: $\ce{CuSO4. 5H2O}$. The dot here is used essentially as an expression of ignorance to indicate that, though the parts of the molecule separated by the dot are bonded to one another in some fashion, the exact structural details of that interaction are not fully expressed in the resulting formula.
Using Alfred Werner’s coordination theory that indicates that four of the five water molecules are actually bonded directly to the $\ce{Cu}$ in the form of a complex aquo ion $\ce{[Cu(H2O)4]^2+}$, then the formula is better expressed as $\ce{[Cu(H2O)4][SO4].H2O}$
So, the dot here signifies ignorance of how the subunits of a formula are structurally related.
The use of dots in phase diagrams
Let's take the example of the ternary phase diagram of $\ce{Na2O}$,$\ce{Al2O3}$,$\ce{SiO2}$. The formulas of the various resulting complex sodium aluminosilicates are all expressed in the form $\ce{a Na2O.b Al2O3.c SiO2}$
in which it is implicitly understood that these initial starting components do not exist as such within the resulting compounds. They represent the combining ratios of the binary/ternary starting materials required for the synthesis of the compound.
For more details, please see http://www.che.uc.edu/Jensen/W.%20B.%20Jensen/Reprints/134.%20Dots.pdf
The use of dots in inorganic chemistry
Let's take the example of copper sulfate penta-hydrate: $\ce{CuSO4. 5H2O}$. The dot here is used essentially as an expression ofignorance to indicate that, though the parts of themolecule separated by the dot are bonded to one another in some fashion, the exact structural details of that interaction are not fully expressed in the resultingformula.
Using Alfred Werner’s coordinationtheory that indicatesthat four of the five water molecules are actuallybonded directly to the $\ce{Cu}$ in the form of a complexaquo ion $\ce{[Cu(H2O)4]^2+}$, then the formula is betterexpressedas $\ce{[Cu(H2O)4][SO4].H2O}$
So, the dot here signifies ignorance of how thesubunits of a formula are structurally related.
The use of dots in phase diagrams
Let's take the example of the ternary phase diagram of $\ce{Na2O}$,$\ce{Al2O3}$,$\ce{SiO2}$. The formulas ofthe various resulting complex sodium aluminosilicatesare all expressed in the form $\ce{a Na2O.b Al2O3.c SiO2}$
in which it is implicitly understood that these initial starting components do not exist as such within the resulting compounds. They represent the combining ratios of the binary/ternary starting materials required for the synthesis of the compound.
For more details, please see http://www.che.uc.edu/Jensen/W.%20B.%20Jensen/Reprints/134.%20Dots.pdf
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By writing $\ce{AB.xCD}$ chemists mean that there are CDs are found in the crystalline framework of AB. The most common example of this is water trapped inside the crystal structure of ionic compounds. (See water of crystallization in wikipedia)
An example that's often taught is $\ce{CuSO4.5H2O}$. See that 5 that's a representative of $x$? It means that water can be bound only with intermolecular interactions, but it exists in the structure in a stoichiometric ratio.
Source
Also, according to this article
As a result, for example in direct addition reactions, where there is ignorance about the structural relation of the compounds, we use a dot.
By writing $\ce{AB.xCD}$ chemists mean that there are CDs are found in the crystalline framework of AB. The most common example of this is water trapped inside the crystal structure of ionic compounds. (See water of crystallization in wikipedia)
An example that's often taught is $\ce{CuSO4.5H2O}$. See that 5 that's a representative of $x$? It means that water can be bound only with intermolecular interactions, but it exists in the structure in a stoichiometric ratio.
Source
Also, according to this article
As a result, for example in direct addition reactions, where there is ignorance about the structural relation of the compounds, we use a dot.
More
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