תרכובות יוניות Ionic compounds Typically occur between metals and nonmetals consist of positive and negative ions. have attractive forces between the positive and negative ions called ionic bonds. have high melting and boiling points. are solid at room temperature.

מלח הוא תרכובת יוניות Sodium chloride, or “table salt,” is an example of an ionic compound.

Formulas of Ionic Compounds נוסחא יונית Formulas of Ionic Compounds The chemical formula of an ionic compound represents the element symbols and subscripts, which represent the lowest whole-number ratio of ions. In the formula of an ionic compound, the sum of positively and negatively charged ions is always zero. the charges are balanced.

a Na atom loses its valence electron. a Cl atom gains an electron. In NaCl, a Na atom loses its valence electron. a Cl atom gains an electron. the symbol of the metal (sodium) is written first, followed by the symbol of the nonmetal (chlorine).

a Mg atom loses two valence electrons. MgCl2 איזון מטענים ב In MgCl2, a Mg atom loses two valence electrons. two Cl atoms gain one electron each. subscripts indicate the number of ions needed to give charge balance. the symbol of the metal (magnesium) is written first, followed by the symbol of the nonmetal (chlorine).

רישום נוסחא יונית מאיזון מטענים Charge balance is used to write the formula for sodium nitride, a compound containing Na+ and N3−.

two Na atoms lose one valence electron each. Na2S איזון מטענים ב In sodium sulfide, Na2S, two Na atoms lose one valence electron each. one S atom gains two electrons. subscripts show the number of ions needed to give charge balance. The group of ions with the lowest ratio of ions in an ionic compound is called a formula unit .

Formula from Ionic Charges רישום נוסחא יונית מאיזון מטענים Formula from Ionic Charges Write the ionic formula of the compound containing Ba2+ and Cl−. Write the symbols of each ion. Ba2+ Cl− Balance the charges. Ba2+ Cl− (two Cl needed) Cl− Write the metal first, followed by the nonmetal, , using a subscript to represent the number of . Cl− ions. BaCl2

תרגיל Learning Check Select the correct formula for each of the following ionic compounds. 1. Na+ and S2– A. NaS B. Na2S C. NaS2 2. Al3+ and Cl– A. AlCl3 B. AlCl C. Al3Cl 3. Mg2+ and N3– A. MgN B. Mg2N3 C. Mg3N2

פתרון Solution Select the correct formula for each of the following ionic compounds. 1. Na+ and S2– B. Na2S 2. Al3+ and Cl– A. AlCl3 3. Mg2+ and N3– C. Mg3N2