Naming of Chemical Compounds: Ionic Compounds, Hydrates

Naming of Chemical Compounds: Please pass the \({\rm{\alpha – D}}\)-glucopyranosyl-\(\left( {{\rm{1,}}\,{\rm{2}}} \right){\rm{ – \beta – D}}\)-fructofuranoside!. Confused? It’s sugar. We come across so many chemicals in our daily life that people mostly know them by their familiar names but not their systematic names. Sugar is also known as sucrose, but asking for it at the dinner table by sucrose will likely be a conversation stopper.

There is a name for each chemical compound. This name should, ideally, indicate the compound’s composition as well as some of its qualities. Such names are known as systematic names, and they are based on a set of \({\rm{IUPAC}}\) standards. Despite the fact that all compounds have systematic names, many of them also have common names. But how do chemical compounds get their names? Let’s explore more about it in this article.

Learn About Haloalkanes Here

Naming Ionic Compounds

Ionic compounds are chemical compounds in which the constituting ions are held together by ionic bonds. These are made up of positively charged metal cations and negatively charged anion or polyatomic ions. Single atoms, such as sodium and chlorine in table salt (sodium chloride), or more complicated (polyatomic) groups, such as carbonate in calcium carbonate, are examples of ions. They must, however, have a positive or negative charge to be considered an ion. The cations and anions combine with each other to form an electrically neutral compound.

Rules for Naming Ionic Compounds

While naming ionic compounds, it is named first by its cation and then by its anion. 

The cation and its element have the same name. \({{\rm{K}}^{{\rm{ + 1}}}}\) is known as the potassium ion, just as \({\rm{K}}\) is known as the potassium atom.

By taking the elemental name, deleting the ending, and adding “\({\rm{ – ide}}\),” the anion is named. \({{\rm{F}}^{{\rm{ – 1}}}}\), for example, is known as fluoride after the element fluorine. The suffix “\({\rm{ – ine}}\)” has been substituted with “\({\rm{ – ide}}\).” The cation name and the anion name are combined to name a compound. For example, sodium fluoride is also known as \({\rm{NaF}}\). If either the cation or the anion was a polyatomic ion, the name of the polyatomic ion is retained and used in the overall compound name. For instance, \({\rm{Ca}}{\left( {{\rm{N}}{{\rm{O}}_{\rm{3}}}} \right)_{\rm{2}}}\) is called calcium nitrate.

The charge is written in Roman numerals in parenthesis immediately following the element name for cations that take on multiple charges (typically transition metals). Because the charge of two nitrate ions \({\rm{N}}{{\rm{O}}_{\rm{3}}}^{{\rm{ – 1}}}\) is \({\rm{2}}\left( {{\rm{ – 1}}} \right){\rm{ = – 2,}}\,{\rm{Cu}}{\left( {{\rm{N}}{{\rm{O}}_{\rm{3}}}} \right)_{\rm{2}}}\) is copper \(\left( {{\rm{III}}} \right)\) nitrate. The \({\rm{Cu}}\) ion has a \({\rm{2 + }}\) charge because the net charge of the ionic compound must be zero. Copper \(\left( {{\rm{II}}} \right)\) nitrate is the name for this chemical.

In simple ionic compounds, the Roman numerals represent the oxidation number, which is always the same as the metal’s ionic charge. The suffixes \({\rm{ – ous}}\) and \({\rm{ – ic}}\) are used to signify the lower and higher positive charges, respectively, in several metallic elements that form cations with varying positive charges. The Latin names of the elements (ferrous/ferric, cuprous/cupric) are used for iron and copper.

However, ions such as \({\rm{C}}{{\rm{a}}^{{\rm{2 + }}}}\) and \({\rm{B}}{{\rm{r}}^{\rm{ – }}}\) can combine only in a \(1:2\) ratio to form neutral calcium bromide, \({\rm{CaB}}{{\rm{r}}_{\rm{2}}}\). There is no need to name it “calcium dibromide” because no alternative formula is possible. \({\rm{CaB}}{{\rm{r}}_{\rm{2}}}\) can be called using the Stock approach or the more traditional method. \({\rm{CuC}}{{\rm{l}}_{\rm{2}}}\), for example, denotes a molecule in which one \({\rm{C}}{{\rm{u}}^{{\rm{2 + }}}}\) cation forms a neutral compound with two \({\rm{C}}{{\rm{l}}^{\rm{ – }}}\) anions. Copper \(\left( {{\rm{II}}} \right)\) chloride is its systematic name, with copper’s oxidation number in parentheses. Cupric chloride was its previous name. 

The Old, Classic, or Common Way of Naming

Naming Molecular Compounds

To signify the number of each element contained in the compound, molecular compounds are named using a systematic approach of prefixes.

When two or more elements share electrons in a covalent bond, they form molecular compounds. Non-metals, in general, share electrons, form covalent bonds, and form molecular compounds.

Rules for Naming Molecular Compounds

1. The ending of the second element is removed, and “\({\rm{ide}}\)” is added, just like in ionic compounds.
2. Prefixes are used to specify the number of a specific element in a compound. “\({\rm{Mono – }}\)” denotes one, “\({\rm{di – }}\)” denotes two, “\({\rm{tri – }}\)” denotes three, “\({\rm{tetra – }}\)” denotes four, “penta-” denotes five, and “\({\rm{hexa – }}\)” denotes six, “hepta-” denotes seven, “\({\rm{octo – }}\)” denotes eight, “\({\rm{nona – }}\)” denotes nine, and “\({\rm{deca}}\)” denotes \(10\). If only one of the first elements is present, the prefix might be omitted. Carbon monoxide, for example, is not written as mono carbon monoxide.
3. The extra vowel at the end of the prefix is eliminated if two vowels in a row sound the same after the prefix is added. One oxygen, for example, should be monooxide, but it’s monoxide instead. The additional ‘\({\rm{o}}\)’ has been removed.

In general, the more electropositive atom is written first, followed by the more electronegative atom, which is then suffixed appropriately. (water), for example, can be referred to as dihydrogen monoxide (though this is not commonly done). This rule does not apply to organic compounds (molecules made up of \({\rm{C}}\) and \({\rm{H}}\) as well as other elements).

Examples of Molecular Compound Names:

• \({\rm{Si}}{{\rm{O}}_{\rm{2}}}\) is called silicon dioxide
• \({\rm{Si}}{{\rm{I}}_{\rm{4}}}\) is called silicon tetraiodide
• \({\rm{S}}{{\rm{F}}_{\rm{6}}}\) is called sulfur hexafluoride
• \({\rm{C}}{{\rm{S}}_{\rm{2}}}\) is called carbon disulfide

Naming Acids and Bases

Base names follow the principles for ionic, organic, or molecular substances, while acid names are based on the anion they form when dissolved in water.

Naming Acids

Acids are named by the anion they form when dissolved in water. It depends on the anion attached to the hydrogen atoms.

Binary acids that have only one hydrogen and an anion with the ending “\({\rm{ – ide}}\) are frequently given names that begin with the prefix “\({\rm{hydro – }}\),” then the anion’s first syllable, and finally the suffix “\({\rm{ – ic}}\).” For instance, \({\rm{HCl}}\), which is made up of hydrogen and chlorine, is called hydrochloric acid.

For complex acids that have oxygen in the compound, there is another simple set of rules.

1. The suffix “\({\rm{ – ic}}\)” is used for any polyatomic ion with the suffix “\({\rm{ – ate}}\)”. As a result, \({\rm{HN}}{{\rm{O}}_{\rm{3}}}\) is nitric acid.
2. The acid will bear the prefix “\({\rm{per – }}\)” and the suffix “\({\rm{ – ic}}\)” if the polyatomic ion has one more oxygen than the “\({\rm{ – ate}}\)” ion. The chlorate ion, for example, is \({\rm{Cl}}{{\rm{O}}_{\rm{3}}}^{\rm{ – }}\). As a result, \({\rm{HCl}}{{\rm{O}}_{\rm{4}}}\) is known as perchloric acid.
3. If the polyatomic ion consists of one oxygen less than the “\({\rm{ – ate}}\)” ion then the acid will have the suffix “\({\rm{ – ous}}\).” For example, chlorous acid is \({\rm{HCl}}{{\rm{O}}_{\rm{2}}}\).
4. The prefix “\({\rm{hypo – }}\)” and the suffix “\({\rm{ – ous}}\)” will be used if the polyatomic ion has two fewer oxygen atoms than the “\({\rm{ – ate}}\)” ion. Instead of bromic acid \(\left( {{\rm{HBr}}{{\rm{O}}_{\rm{3}}}} \right)\), hypobromous acid \(\left( {{\rm{HBrO}}} \right)\) is used.

Naming Bases

Hydroxide, a polyatomic ion, is found in most strong bases. As a result, strong bases are named according to the naming conventions for ionic compounds. For example, sodium hydroxide is \({\rm{NaOH}}\), potassium hydroxide is \({\rm{KOH}}\), and calcium hydroxide is \({\rm{Ca}}{\left( {{\rm{OH}}} \right)_{\rm{2}}}\). The ionic naming methodology is also used to name weak bases constituted of ionic compounds. Ammonium hydroxide, for example, is \({\rm{N}}{{\rm{H}}_{\rm{4}}}{\rm{OH}}\).

Because of their covalent bonds, weak bases are sometimes referred to as molecular or organic compounds. As a result, they are given names that follow the guidelines for naming molecular or chemical compounds. Methylamine \(\left( {{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{N}}{{\rm{H}}_{\rm{2}}}} \right)\), for example, is a weak base. Some “common” names exist for weak bases. For example, \({\rm{N}}{{\rm{H}}_{\rm{3}}}\) is known as ammonia, despite the fact that its name is not derived from any naming system.

Naming Hydrates

The term “hydrate” is used in both inorganic and organic chemistry to describe a substance that contains loosely bound water molecules.

Inorganic Hydrates

The ionic compound’s name is preceded by a number prefix and the suffix -hydrate. \({\rm{CuS}}{{\rm{O}}_{\rm{4}}}{\rm{.5}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\), for example, is “copper\(\left( {{\rm{II}}} \right)\) sulphate pentahydrate.”

The hydrous compound is denoted by \({\rm{n}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\), where n is the number of water molecules per formula unit of the salt. It is commonly used to show that salt is hydrated. The “⋅” indicates that the water is loosely bonded to the ionic compound. The “\({\rm{n}}\)” usually takes a low integer value though it is possible for fractional values to exist. The prefixes used are the same Greek prefixes used in naming molecular compounds. 

For numbers \(1/2\) through \(10\), the Greek prefixes used in naming hydrates are as follows:

• \({\rm{1/2: hemi – }}\)
• \({\rm{1: mono – }}\)
• \({\rm{2: di – }}\)
• \({\rm{3: tri – }}\)
• \({\rm{4: tetra – }}\)
• \({\rm{5: penta – }}\)
• \({\rm{6: hexa – }}\)
• \({\rm{7: hepta – }}\)
• \({\rm{8: octa – }}\)
• \({\rm{9: nona – }}\)
• \({\rm{10: deca – }}\)

Anhydride refers to a hydrate that has lost its water. Only significant heating causes an anhydride to lose water. Anhydrous refers to a substance that no longer contains any water.

Organic Hydrates

Hydrates are less common in organic chemistry. A compound formed by the addition of water or its components to another molecule is known as an organic hydrate. For example, ethanol, \({\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{ – C}}{{\rm{H}}_{\rm{2}}}{\rm{ – OH}}\), is a hydrate of ethene, \({\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{ = C}}{{\rm{H}}_{\rm{2}}}\), which is formed by adding \({\rm{H}}\) to one \({\rm{H}}\) and \({\rm{OH}}\) to the other. Another example is chloral hydrate \({\rm{(CC}}{{\rm{l}}_{\rm{3}}}{\rm{ – CH}}{\left( {{\rm{OH}}} \right){_\rm{2}}}\), which is generated when water reacts with chloral \(\left( {{\rm{CC}}{{\rm{l}}_{\rm{3}}}{\rm{ – CH = O}}} \right)\).

Summary

An empirical or molecular formula, each consisting of at least one formula unit, is used to represent the composition of a compound. Hydrocarbons are named using a method based on the number of bonds between carbon atoms, whereas covalent inorganic compounds are named using a procedure similar to that used for ionic compounds. The relative numbers of atoms of the elements in a compound are given by an empirical formula, which is reduced to the lowest whole numbers. The formula unit is the absolute grouping represented by an ionic or covalent compound’s empirical formula. We learned how to name chemical substances in this essay. We also learned how to name acids, bases, organic and inorganic hydrates according to certain rules.

FAQs

Q.1. How are ionic compounds named?
Ans: The cation comes first in naming ionic substances, followed by the anion. The balance of positive and negative charges must be maintained.

Q.2. How do you name chemical compounds?
Ans: In most cases, a molecular compound is made up of two or more nonmetal elements. The first element is named first, followed by the second element, using the stem of the element name plus the suffix \({\rm{ – ide}}\). The number of atoms in a molecule is specified using numerical prefixes.

Q.3. How are ionic compounds represented?
Ans: Binary ionic compounds (ionic compounds containing only two types of elements) are named by first writing the name of the cation and then the name of the anion. Potassium chloride, for example, is an ionic compound that contains both \({{\rm{K}}^{\rm{ + }}}\) and \({\rm{C}}{{\rm{l}}^{\rm{ – }}}\)  ions.

Q.4. How is the water of crystallisation represented in naming compounds?
Ans: The hydrous compound is denoted by \({\rm{n}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\), where n is the number of water molecules per formula unit of the salt. It is commonly used to show that salt is hydrated. The “\( \cdot \)” indicates that the water is loosely bonded to the ionic compound. For example, \({\rm{CuS}}{{\rm{O}}_{\rm{4}}}{\rm{.5}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\).

Q.5. How do you name molecular compounds?
Ans: In general, the more electropositive atom is written first, followed by the more electronegative atom, which is then suffixed appropriately. For example, water can be referred to as dihydrogen monoxide (though this is not commonly done). This rule does not apply to organic compounds (molecules made up of \({\rm{C}}\) and \({\rm{H}}\) as well as other elements).

The ending of the second element is removed, and “\({\rm{ide}}\)” is added, just like in ionic compounds.

Prefixes are used to specify the number of a specific element in a compound. “\({\rm{Mono – }}\)” denotes one, “\({\rm{di – }}\)” denotes two, “\({\rm{tri – }}\)” denotes three, “\({\rm{tetra – }}\)” denotes four, and so on. If only one of the first element is present, the prefix might be omitted. The extra vowel at the end of the prefix is eliminated if two vowels in a row sound the same after the prefix is added.

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