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Atoms, Molecules and Ions Study Guide (page 3)

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Updated on Sep 24, 2011

Type I and II Binary Compounds

Type I and II binary compounds are neutral, ionic compounds that contain two parts: a cation and an anion. When a metal is the cation and a nonmetal is an anion, the following rules are used:

  • The cation is always listed first and the anion second.
  • For cations that possess multiple ions (see Figure 2.1), the charge on the ion must be specified by using a Roman numeral in parentheses following the cation.

Figure 2.1 Common Cations and Anions

Type I and II compounds are neutral and charges must balance to create a net zero charge.

Chemical Composition Atoms, Molecules, and Ions

Polyatomic Ions

Polyatomic ions are ions that contain more than one atom (see Table 2.2). These ions can replace one or both ions in Type I or II ionic compounds and have special names. However, the oxyanions (the ions containing oxygen) have a systematic naming structure. When two oxyanions of an element are present, the anion with the larger number of oxygen atoms is given the suffix -ate (i.e., sulfate, SO4 2–, and nitrate,NO3–), and the anion with the smaller number of oxygen atoms is given the suffix -ite (i.e., sulfite, SO32–, and nitrite, NO2).When more than two oxyanions exist in a series, the prefixes hypo- (less than) and per- (more than) are used, as in chlorine and bromine oxyanions.

Table 2.2 Common Polyatomic Ions

Chemical Composition Atoms, Molecules, and Ions

Table 2.3 Numerical Pre?xes Used in Chemical Names

Type III: Binary Covalent Compounds

Type III binary compounds are neutral, covalent compounds that contain two nonmetals. Type III naming is similar to Type I and II using the following rules:

  • The element listed first is named first using the full element name.
  • The element listed second is named as if it were an anion.
  • A prefix is used to represent the number of atoms because nonmetals can combine in many different ways (see Table 2.3). The prefix mono- is not used for the first element.

Chemical Composition Atoms, Molecules, and Ions

Some covalent molecules use a common name over their systematic name. Examples include H2O (water), NH3 (ammonia), CH4 (methane), and BH3 (borane).

Acids

Acids are substances that donate positive hydrogen ions (H+) when dissolved in water. Adding one or more hydrogens to an anion requires a different name.

For anions ending in -ide, use a hydro- prefix and an -ic acid ending. For example, what is the chemical name for HCl and HCN?

Chemical Composition Atoms, Molecules, and Ions

For oxyanions (polyatomic ions containing oxygen), use an -ic acid ending for polyatomic ions ending in -ate and -ous ending for polyatomic ions ending in -ite. For example, what is the chemical name for H2SO4 and H2SO3?

Chemical Composition Atoms, Molecules, and Ions

Practice problems for these concepts can be found at -  Atoms, Molecules and Ions Practice Questions

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