Ionic Bonding (Part II) Ionic Compounds: The Compounds that Result from Ionic Bonding

 Compounds in which two or more ions are held together by electrical attraction.  The positive ions are called cations.  The negative ions are called anions.  Ionic compounds usually form large crystals that can be seen with the naked eye.  Ionic compounds with smaller crystals may appear as powders. What are Ionic Compounds?

 All ionic compounds form crystals—the attraction between cations and anions is conducive to the ordered stacking that makes up crystals.  Ionic compounds tend to have high melting and boiling points—to break the positive and negative charges apart for either melting or boiling, it takes a huge amount of energy. Properties of Ionic Compounds

 All ionic compounds are very hard and brittle. It takes a lot of energy to pull ionic charges apart. If one gives a large crystal a strong enough impact, such as that from a hammer, one typically uses so much energy that the crystal doesn't break in only one place. Instead, it shatters.  When ionic compounds dissolve in water, they yield solutions that conduct electricity. The positive and negative ions that become separated from each other in a water solution allow electrons to flow much better than in plain water. Ionic compound are often called salts and salt-water conducts electricity. Properties of Ionic Compounds

Remember its based on the Octet Rule NaCl + - NaCl Formation of an Ionic Bond Using Lewis Dot Diagrams

 METAL + NONMETAL  Important metal ions  Group 1A loses 1 electron (+1)  Group 2A loses 2 electrons (+2)  Group 3A loses 3 electrons (+3)  Important non-metal ions  Group 7A gains 1 electron (-1)  group 6A gains 2 electrons (-2)  group 5A gains 3 electrons (-3)  Group 4A gains 4 electrons (-4) Ionic Compound

 For a cation with a +1 charge and an anion with a -1 charge, it’s easy: Example: NaCl  For a cation with a +2 charge and an anion with a -2 charge, it’s also easy: Example: MgO.  Similarly, for a cation with a +3 charge and an anion with a -3 charge, it’s easy. For Ionic Compounds, the Total Charge of the Cations Must Balance the Total Charge of the Anions

 One approach is basically mathematical:  For Ca (Group 2A) with a +2 charge and P (Group 5A) with a -3 charge, one needs (3 times +2) for the cations and (2 times -3) for the anions to balance. This is shown here with interlocking blocks: Ca 3 P 2. For Cations and Anions with Different Values of Charge, Balancing is More Difficult Ca 2+ P 3-

Ca 2+ and P Gives Ca 3 P 2 But, Mg 2+ and O 2- (Mg + O 2 Reaction) 2 2 Gives Mg 2 O 2 which must be changed to the simpler MgO! Be careful when you use Criss Cross! The Reaction of Ca and P (Another Method: Criss Cross)

Mg 2+ and C Gives Mg 4 C 2 By convention, Mg 4 C 2 must be changed to the simpler Mg 2 C, when both ion subscripts are divisible by 2. Be careful when you use Criss Cross! The Reaction of Mg and C (A Criss Cross Example with an Adjustment)

 The reaction of aluminum and sulfur yields:  Aluminum is in Group 3A. Charge of 3+ Al 3+  Phosphorus is in Group 6A. Charge of 2- S 2-  A 3+ and a 2- cannot balance simply: AlS would have a net +1 charge. Another Example Problem For Cations and Anions with Different Values X

Al 3+ and S Gives Al 2 S 3 But, Al 3+ and N 3- (Al + N 2 Reaction) 3 3 Gives Al 3 N 3 which must be changed to the simpler AlN! The Reaction of Al and S (Method 1: Criss Cross)

 For Al 3+ and S 2-, the lowest common denominator is 6 (plus or minus).  Therefore, one should try for a +6 balancing a -6.  2 times +3 is +6. So one needs 2 Al 3+.  3 times -2 is -6. So, one needs 3 S 2-.  Putting them together gives Al 2 S 3.  This method always works. The Reaction of Al and S (Method 2: Mathematical Balance)

 For one Al 3+ and one S 2-, the combination would be AlS + with a net charge of +1.  WRONG; it has to be neutral.  For one Al 3+ and two S 2-, the combination would be AlS 2 - with a net charge of -1.  WRONG; it has to be neutral.  For two Al 3+ and two S 2-, the combination would be Al 2 S 2 2+ with a net charge of +2.  WRONG; it has to be neutral.  For two Al 3+ and three S 2-, the combination would be Al 2 S 3 with a net charge of 0. CORRECT! The Reaction of Al and S (Method 3: Trial and Error)

 Use the correctly charged blocks for both the cation and anion.  Fit them together to form a rectangle.  The number of cation blocks is the subscript for the cation: Al 2  The number of anion blocks is the subscript for the anion: S 3  Put the components together into a proper chemical formula: Al 2 S 3. The Reaction of Al and S (Method 4: Charge-Balance Interlocking Blocks) S 2- Al 3+

 Find the correct charges for the cation and anion from their Periodic Table Group.  Use the method that works best for you.  Criss Cross  Mathematical Balance  Trial and Error  Charge-Balance Interlocking Blocks  Check the result to see that it is balanced and in the simplest possible form. Charge Balanced Ionic Compounds

 The reaction of lithium with carbon.  Li 4 C Practice Example

 The reaction of aluminum with fluorine.  AlF 3 Practice Example

 Simple ionic compounds have two word names.  The first word is the name of the cation, which is just the name of the element.  The second word is the name of the anion, which is not simply the name of the element. This anion name is derived from the element name. Specifically, the last part of the element name is replaced with -ide. Rules for Naming Simple Ionic Compounds

 Oxygen becomes oxide.  Hydrogen becomes hydride.  Carbon becomes carbide. (The suffix part of the element name beginning with a vowel—a, e, i, o, u, or y—is replaced with the suffix -ide). Examples of Anion Names

 NaBr  Mg 3 P 2  AlN  Na 2 O Naming Examples Sodium bromide Magnesium phosphide Aluminum nitride Sodium oxide