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ChemLab113-0015 - It can be seen from Table 1 that most...

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Unformatted text preview: It can be seen from Table 1 that most common cations are monatomic. Many elements form only a single type of monatornic cation. For example, Na+ is the only monatomic cation of sodium. No compound is known that contains sodium ions with charges greater than plus one. The cations of elements that form only one type of monatomic cation are given the names of the elements. For example, Na+ is named the sodium ion. Some elements, such as iron and copper, form two or more different monatomic cations. Table 1 shows that iron forms Fe2+ and 1363+, while copper forms Cu+ and Cur“. There are two difl'erent systems for naming cations in cases in which two or more different cations are formed by an element. The modem system uses Roman numerals to indicate the electron deficits. For example, Fe2+ is named the iron (H) ion, and Fe3+ is named the iron (Ill) ion. The modern system is used in Table 1, and it is the one we will use in this course. An older system, which is still in use, employs stems derived from the Latin names of the elements. For elements that form two different monatomic cations, the stems are combined with the endings w and i_c to indicate the ions with the smaller charge and larger charge, respectively. For example, the stem for iron is fe_rr, and the ions Fe2+ and F e3+ are named the ferrous ion and the m ion, respectively. Many elements form monatomic anions instead of monatomic cations. An example is chlorine, which forms the Cl‘ ion. Each element that forms monatomic anions forms only a single type. For example, Cl' is the only monatomic anion formed by chlorine. Monatornic anions are named by combining a stem formed fiom the name of the element with the ending id_e. For example, Cl' is named the chloride ion. Table 1 contains the names and formulas of several polyatomic ions. The naming of polyatomic ions is relatively complicated. Consequently, it is probably easier to memorize the names given rather than consider the set of rules for obtaining them. The names and formulas of ions in Table 1 can be used to obtain the names and formulas of a large number of ionic compounds. To obtain the formulas of ionic compounds we use the film that all ionic compounds are electrically neutral. Consequently, the formula of any ionic compound must be such that the sum of the anion and cation charges in the formula unit is Lego. We also use the fact that the formulas of ionic compounds are simplest formulas only. The formula unit in an ionic compound is the smallest collection of ions with charges that add to zero. In addition, we use the convention that cations are given before anions in the formulas of ionic compounds. 24 ...
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