Ionic bonds are formed by the transfer of one or more valence electrons between atoms, typically between metals and nonmetals.
The transfer of electrons allows the atoms to effectively achieve the much more stable electron configuration of having eight electrons in the outermost valence shell octet rule. When sodium donates a valence electron to fluorine to become sodium fluoride, that is an example of ionic bond formation. Ionic compounds can be described using chemical formulas, which represent the ratios of interacting elements that are found in the ionic solid or salt.
Ionic solids are typically represented by their empirical formulas. In formula notation, the elements are represented by their chemical symbols followed by numeric subscripts that indicate the relative ratios of the constituent atoms. The complete formula for an ionic compound can be determined by satisfying two conditions:. Name the following ionic compounds, which contain a metal that can have more than one ionic charge:.
These charges are used in the names of the metal ions:. Chemists use nomenclature rules to clearly name compounds. Ionic and molecular compounds are named using somewhat-different methods. Binary ionic compounds typically consist of a metal and a nonmetal. The name of the metal is written first, followed by the name of the nonmetal with its ending changed to — ide. For example, K 2 O is called potassium oxide. If the metal can form ions with different charges, a Roman numeral in parentheses follows the name of the metal to specify its charge.
Some compounds contain polyatomic ions; the names of common polyatomic ions should be memorized. Molecular compounds can form compounds with different ratios of their elements, so prefixes are used to specify the numbers of atoms of each element in a molecule of the compound. Examples include SF 6 , sulfur hexafluoride, and N 2 O 4 , dinitrogen tetroxide. When crossing charges, it is sometimes necessary to reduce the subscripts to their simplest ratio to write the empirical formula.
Using the absolute values of the charges on the ions as subscripts gives the formula Pb 2 O 4. This simplifies to its correct empirical formula PbO 2. The rule for constructing formulas for ionic compounds containing polyatomic ions is the same as for formulas containing monatomic single-atom ions: the positive and negative charges must balance.
If more than one of a particular polyatomic ion is needed to balance the charge, the entire formula for the polyatomic ion must be enclosed in parentheses, and the numerical subscript is placed outside the parentheses. This is to show that the subscript applies to the entire polyatomic ion. Two examples are shown below:. There are two ways to recognize ionic compounds. First, compounds between metal and nonmetal elements are usually ionic.
For example, CaBr 2 contains a metallic element calcium, a group 2A metal and a nonmetallic element bromine, a group 7A nonmetal. Therefore, it is most likely an ionic compound. In fact, it is ionic. In contrast, the compound NO 2 contains two elements that are both nonmetals nitrogen, from group 5A, and oxygen, from group 6A. It is not an ionic compound; it belongs to the category of covalent compounds discuss elsewhere.
Also note that this combination of nitrogen and oxygen has no electric charge specified, so it is not the nitrite ion.
Second, if you recognize the formula of a polyatomic ion in a compound, the compound is ionic. Remember that the convention for writing formulas for ionic compounds is not to include the ionic charge. Use parentheses where required.
The name of this ionic compound is simply calcium nitrate. Write the proper formula and give the proper name for each ionic compound formed between the two listed ions. In fact, the human body is approximately 0. Sodium is also present in our diet. The common table salt we use on our foods is an ionic sodium compound.
Many processed foods also contain significant amounts of sodium added to them as a variety of ionic compounds. Why are sodium compounds used so much? Usually sodium compounds are inexpensive, but, more importantly, most ionic sodium compounds dissolve easily. This allows processed food manufacturers to add sodium-containing substances to food mixtures and know that the compound will dissolve and distribute evenly throughout the food. Simple ionic compounds such as sodium nitrite NaNO 2 are added to cured meats, such as bacon and deli-style meats, while a compound called sodium benzoate is added to many packaged foods as a preservative.
Some of them you may recognize after reading this chapter. Others you may not recognize, but they are all ionic sodium compounds with some negatively charged ion also present. The use of so many sodium compounds in prepared and processed foods has alarmed some physicians and nutritionists. They argue that the average person consumes too much sodium from his or her diet. The average person needs only about mg of sodium every day; most people consume more than this—up to 10 times as much.
Some studies have implicated increased sodium intake with high blood pressure; newer studies suggest that the link is questionable. Skip to content Chapter 3. Atoms, Molecules, and Ions. Know how ions form. Learn the characteristic charges that ions have. Construct a proper formula for an ionic compound. Generate a proper name for an ionic compound. Problems Name each species. Anions are named using the stem of the element name with the suffix -ide added.
This is the oxide anion. Because this species has no charge, it is an atom in its elemental form. This is cobalt.
We note from Table 3. This is the cobalt II cation. Test Yourself Name each species. Problems Write the proper ionic formula for each of the two given ions. This means we have to go to a least common multiple, which in this case will be six. Hence the proper ionic formula is Al 2 O 3.
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