Naming Binary Molecular Compounds

Example: N2O

The first element is always named first using the entire element name, N is the symbol for nitrogen.

The second element is named using its root and adding the suffix -ide, O is the symbol for oxygen so the second word is oxide.

Prefixes are used to indicate the number of atoms of each element that are present in the compound, There are two atoms of nitrogen and one atom of oxygen so the first word is dinitrogen and the second word is monoixide.

Naming MoleculesCopyright © McGraw-Hill Education

Naming MoleculesCopyright © McGraw-Hill Education

NAMING BINARY MOLECULAR COMPOUNDS

Use with Example Problem 2.

Problem Name the compound P2O5, which is used as a drying and dehydrating agent.ResponseANALYZE THE PROBLEM

You are given the formula for a compound. The formula contains the elements and thenumber of atoms of each element in one molecule of the compound. Because only twodifferent elements are present and both are nonmetals, the compound can be named using the rules for naming binary molecular compounds.

SOLVE FOR THE UNKNOWN

• The first element, represented by P, is phosphorus.

Phosphorus

• The second element, represented by O, is oxygen. Add the suffix –ide to the root of oxygen, ox-.

Oxide

• Combine the names.

Phosphorus oxide

Now modify the names to indicate the number of atoms present in a molecule.

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Naming Binary Molecular Compounds

EVALUATE THE ANSWER

The name diphosphorus pentoxide shows that a molecule of the compound contains two phosphorus atoms and five oxygen atoms, which agrees with the compound’s chemical formula, P2O5.

SOLVE FOR THE UNKNOWN

• From the formula P2O5, you know that two phosphorus atoms and five oxygen atoms make up a molecule of the compound. From Table 3, you know that di- is the prefix for two and penta- is the prefix for five. The a in penta- is not used because oxide begins with a vowel.

diphosphorus pentoxide

Naming Binary Molecular Compounds

Many compounds were discovered and given common names long before the present naming system was developed (water, ammonia, hydrazine, nitric oxide).

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Naming Acids

Binary Acids (An acid that contains hydrogen and one other element)

Example: HCl

The first word has the prefix hydro- to name the hydrogen part of the compound. The rest of the word consists of a form of the root of the second element plus the suffix –ic, HCl (hydrogen and chlorine) becomes hydrochloric.

The second word is always acid, Thus, HCl in a water solution is called hydrochloric acid.

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Naming Acids

An oxyacid is an acid that contains both a hydrogen atom and an oxyanion.

Example: HNO3

Identify the oxyanion present. The first word of an oxyacid’s name consists of the root of the oxyanion and the prefix per- or hypo- if it is part of the name and a suffix. If the oxyanion’s name ends with the suffix –ate, replace it with the suffix –ic. If the name of the oxyanion ends with suffix –ite, replace it with suffix –ous, NO3

– the nitrate ion, becomes nitric.

The second word of the name is always acid, HNO3 (hydrogen and nitrogen ion) becomes nitric acid.

Naming MoleculesCopyright © McGraw-Hill Education

Naming Acids

Naming MoleculesCopyright © McGraw-Hill Education

Naming Acids

An acid, whether a binary acid or an oxyacid, can have a common name in addition to its compound name.

Naming MoleculesCopyright © McGraw-Hill Education

Writing Formulas from Names

The name of a molecular compound reveals its composition and is important in communicating the nature of the compound.

The flowchart can help you determine the name of a molecular covalent compound.

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