![]() Now the positive and negative charges are balanced. The easiest way to balance these charges is to assume the presence of two chloride ions for each magnesium ion: Mg 2+ Cl − Cl − A magnesium ion has a 2+ charge, while a chlorine ion has a 1− charge: Mg 2+ Cl −Ĭombining one ion of each does not completely balance the positive and negative charges. Now consider the ionic compound formed by magnesium and chlorine. Therefore, the proper formula for this ionic compound is MgO. Although both of these ions have higher charges than the ions in lithium bromide, they still balance each other in a one-to-one ratio. When an ionic compound is formed from magnesium and oxygen, the magnesium ion has a 2+ charge, and the oxygen atom has a 2− charge. Only one ion of each is needed to balance these charges. If we look at the ionic compound consisting of lithium ions and bromide ions, we see that the lithium ion has a 1+ charge and the bromide ion has a 1− charge. ![]() Each ion is surrounded by ions of opposite charge.īy convention, assume that there is only one atom if a subscript is not present. ![]() Although it is convenient to think that NaCl crystals are composed of individual NaCl units, Figure 3.6 "A Sodium Chloride Crystal" shows that no single ion is exclusively associated with any other single ion. A macroscopic sample is composed of myriads of NaCl pairs each pair called a formula unit A set of oppositely charged ions that compose an ionic compound. Thus, NaCl is the chemical formula for sodium chloride, which is a concise way of describing the relative number of different ions in the compound. In the case of sodium chloride, the ratio of sodium ions to chloride ions, expressed in lowest whole numbers, is 1:1, so we use NaCl (one Na symbol and one Cl symbol) to represent the compound. However, we can use the ratio of sodium ions to chloride ions, expressed in the lowest possible whole numbers, as a way of describing the compound. As you can see, there are no individual NaCl “particles” in the array instead, there is a continuous lattice of alternating sodium and chloride ions. ( Figure 3.6 "A Sodium Chloride Crystal"). Ionic compounds exist as alternating positive and negative ions in regular, three-dimensional arrays called crystals A three-dimensional array of alternating positive and negative ions. ![]() To better understand what a chemical formula means, we must consider how an ionic compound is constructed from its ions. is a concise list of the elements in a compound and the ratios of these elements. A chemical formula A concise list of the elements in a compound and the ratios of these elements. We have already encountered some chemical formulas for simple ionic compounds.
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