Ionic Compounds

Physical Science - Middle School

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Ionic Compounds © Copyright NewPath Learning. All Rights Reserved. 94-4840 Visit www.newpathlearning.com for Online Learning Resources. Naming Ionic Compounds The names of ionic compounds are written by listing the name of the positive ion followed by the name of the negative ion. Therefore, a series of rules is needed to name the positive and negative ions before we can name these compounds. Sodium Chloride Potassium Chloride Aluminum Phosphide Magnesium Sulde Cl Na + P Al 3+ 3– Cl K + S Mg 2+ 2– 1+ 1– += 0 2+ 2– += 0 1+ 1– += 0 3+ 3– += 0 Sodium Chloride Potassium Chloride Aluminum Phosphide Magnesium Sulde Cl Na + P Al 3+ 3– Cl K + S Mg 2+ 2– 1+ 1– += 0 2+ 2– += 0 1+ 1– += 0 3+ 3– += 0 Single atomic positive ions have the name of the element from which they are formed. However, since some metals form positive ions in more than one oxidation state, (ex. Fe2+, Fe3+) the charge on the ion is indicated by a Roman numeral in parentheses immediately after the name of the element (Ex. iron(II), iron(III)). single atomic negative ions Oxide Fluoride Chloride O2– F– Cl– Sul de S2– Bromide Br– Iodide I– Nitrate Sulfate SO 4 2– Chlorate ClO 3 NO 3 Nitrite Sul te SO 3 2– Chlorite ClO 2 NO 2 polyatomic negative ions low oxidation state high oxidation state Hydrogen Sodium single atomic positive ions Potassium H+ Na+ K+ Calcium Ca2+ Iron (II) Fe2+ Iron (III) Fe3+ polyatomic positive ions Hydronium H 3O + Ammonium NH 4 + Hydrogen Sodium single atomic positive ions Potassium H+ Na+ K+ Calcium Ca2+ Iron (II) Fe2+ Iron (III) Fe3+ polyatomic positive ions Hydronium H 3O + Ammonium NH 4 + Negative ions that consist of a single atom are named by adding the suffix “-ide” to the stem of the name of the element. Polyatomic Negative Ions The name of polyatomic negative ions usually ends in either “-ite” or “- ate.” The “-ite” ending indicates a low oxidation state (nitrite ion NO2-). The “–ate” ending indicates a high oxidation state (nitrate ion NO3-). Oxidation State Oxidation state shows the total number of electrons that an atom has gained or lost in order to form a chemical bond with another atom. Writing Formulas for Ionic Compounds When an ionic compound is formed, the ions must combine in a way that the total charges of the compound equal zero. For example, let’s write the correct formula for magnesium chloride. The first step is to write the formulas for the cation Mg2+ and anion Cl-. Next, drop the positive and negative signs; crisscross the superscripts so that they become subscripts and reduce when possible by finding the least common multiple. In this example, the two chlorine ions, with a total charge of -2, balance the +2 charge of the magnesium ion. The cation is always listed first before the anion, resulting in the formula MgCl 2. +3 2(-2) +5 3(-2) oxidation state low oxidation state high oxidation state Nitrate NO 3 Nitrite NO 2 NO 2 NO 3 N +3 +3 2(-2) +5 3(-2) oxidation state low oxidation state high oxidation state Nitrate NO 3 Nitrite NO 2 NO 2 NO 3 N +3 Mg2 Mg2+ Cl– Magnesium Chloride anion (-) cation (+) 1 2 Cl 2 Mg 2 Cl 3 2+ 2(–) += 0 Polyatomic (more than two atoms) positive ions often have common names ending with the suffix “-onium” such as hydr onium (H3O+) or ammonium (NH4+). single atomic negative ions Oxide Fluoride Chloride O2– F– Cl– Sul de S2– Bromide Br– Iodide I– Nitrate Sulfate SO 4 2– Chlorate ClO 3 NO 3 Nitrite Sul te SO 3 2– Chlorite ClO 2 NO 2 polyatomic negative ions low oxidation state high oxidation state
Ionic Compounds Pause and Review Name the following compounds. 1) K2S __________________________________________________________________ 2) CaBr2 _________________________________________________________________ 3) HI ____________________________________________________________________ 4) SrF2 __________________________________________________________________ 5) Be3P2 _________________________________________________________________ 6) Al2O3 _________________________________________________________________ 7) BCl3 __________________________________________________________________ Write the formula for the following ionic compounds. 1) Magnesium Chloride ___________________________________________________ 2) Sodium Nitride ________________________________________________________ 3) Sodium Chlorate _______________________________________________________ 4) Potassium Nitrate ______________________________________________________ 5) Calcium Chlorate ______________________________________________________ 6) Aluminum Nitrite ______________________________________________________ 7) Aluminum Nitrate _____________________________________________________ © Copyright NewPath Learning. All Rights Reserved. 94-4840 Visit www.newpathlearning.com for Online Learning Resources.