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Chapter 6 Ionic and Molecular Compounds. 6.2 Writing Formulas for Ionic Compounds Learning Goal Using charge balance, write the correct formula for an ionic compound. Ionic Compounds. Ionic compounds consist of positive and negative ions.
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Chapter 6 Ionic and Molecular Compounds 6.2 Writing Formulas for Ionic Compounds Learning Goal Using charge balance,write the correct formula for an ionic compound.
Ionic Compounds Ionic compounds consist of positive and negative ions. Ions are held together by the strong electrical attractions between opposite charges, called an ionic bond. Noble gases have a stable electron configuration and do not form ionic compounds.
Properties of Ionic Compounds The physical and chemical properties of elements change when they react to form ionic compounds.
Properties of Ionic Compounds Figure 6.1 The elements sodium and chlorine react to form the ionic compound sodium chloride, the compound that makes up table salt. The magnification of NaCl crystals shows the arrangement of Na+ ions and Cl– ions in a crystal of NaCl.
Chemical Formulas of Ionic Compounds The chemical formula of a compound represents the symbols and numbers of atoms or ions in the lowest whole-number ratio. The sum of the ionic charges is always zero.
Subscripts in Formulas Two chlorine atomsare needed to reactwith one magnesiumatom to give thecompound magnesiumchloride (MgCl2)charge balance. Subscripts in an ionic compound represent the lowest number of positive and negative ions that give an overall charge of zero.
Writing Ionic Formulas from Ionic Charges To write the formula of a compound that contains Na+ and S2− • metal ions are written first, followed by an ion from a nonmetal • two Na+ ions needed for charge balance are represented using a subscript in the formula • the subscript for the nonmetal S2− is 1 (it is understood and not written in the formula)
Writing Ionic Formulas from Ionic Charges The group of ions that contains the lowestratio of ions in an ionic compound is called aformula unit.
Learning Check Use charge balance to write the formula for lithium nitride, a compound containing Li+and N3−.
Solution Use charge balance to write the formula for lithium nitride, a compound containing Li+and N3−.
Learning Check Use charge balance to write the ionic formula of the compound containing Ba2+ and Cl−.
Solution Use charge balance to write the ionic formula of the compound containing Ba2+ and Cl−.
Learning Check Select the correct formula for each of the following ionic compounds: A. Li+ and O2− (1) LiO (2) Li2O (3) LiO2 B. Al3+ and Cl− (1) AlCl3 (2) AlCl (3) Al3Cl C. Mg2+ and N3− (1) MgN (2) Mg2N3 (3) Mg3N2
Solution Select the correct formula for each of the following ionic compounds: A. Li+ and O2− (2) Li2O B. Al3+ and Cl− (1) AlCl3 C. Mg2+ and N3− (3) Mg3N2