Ionic Bonding By: Kiri Tamte-Horan

Before we talk about ionic bonds… Understand that ionic bonding is a form of chemical bonds Chemical bonds are formed by the joining of two or more atoms Other forms of chemical bonds include: Covalent Bonds Metallic Bonds

What are ionic bonds? Electrostatic forces that bind oppositely charged ions together FOR EXAMPLE, NaCl CLICK HERE TO LEARN MORE!

What’s the difference between Ionic and Covalent bonding? The difference is in the electronegativity Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons Most bonds are a combination of both Ionic and Covalent Bonds “True” Covalent Bond  0.00 - .4 (pure covalent) 50:50 Bond 1.67 Greater than 1.67 is ionic (number varies) Less than 1.67 is covalent (polar)

Coulomb’s Law where: F = force K = constant q1 & q2 = charges d = distance between centers *as the charges increase force increases *as the distance between the centers increase force decreases

Lewis-dot Symbols They only depict valence electrons (octet) Electrons are represented as dots The number of valence electrons are shown by the dots surrounding the element The electrons are added clockwise around the element Remember the Aufbau Principle! If you forget what that means, it means that you must fill the fill the lowest energy states first

Lewis-dot Symbols cont… Lewis Dot Diagrams of Selected Elements

Properties of Ionic Bonds Crystalline solids “crystal lattice” (unit cells) Very high melting point Do not conduct as a solid But, do conduct as a liquid Dissolve in Water Commonly called salts

Ionic Reactions 2 Na Let’s bond Na and Cl! The one valence electron from Na is transferred to Cl, making Cl have the electron configuration of a noble gas. Na becomes 1+ Cl becomes 1- 2 Na

Born Haber Calculations The Born Haber Cycle is a thermodynamic cycle that analyzes lattice energy Lattice Energy is an estimate of the strength of the bonds in an ionic compound To find the lattice energy we must use the BORN HABER CYCLE Let’s find out what that is!

Born Haber Cycle Let’s use this example! 4Ga + 3 O2  2 Ga2O3 First we must DIVIDE through by the coefficient of the compound formed In this case, that number is 2 So, 2Ga + 3/2 O2  Ga2O3 Now let’s go through the steps of the Cycle!

Step One Vaporize the metal into the gaseous state using Heat of Sublimation Since our metal is Ga, we must find the value for the Heat of Sublimation for Ga. In this case, the number is 262 KJ Now, since there are 2 Ga, we must multiply 262 by 2! The equation looks like this 2Ga(s)  2Ga(g) Make sure you write in the states of matter!

Step Two Ionize the metal atom to the state of charges using the Ionization Energy We use the vaporized metal from Step One  2Ga(g) For this step, we must first find out how many electrons Ga loses, which turns out to be three Then, look up the Ionization energy for Ga, which is 2989 KJ Like the previous step, we must multiply this number by two, since Ga has a coefficient of 2 2Ga(g)  2Ga 3+ + 6e- You get the 6e- from multiplying the coefficient by the number of electrons lost

Step Three Dissociate the non-metal molecule into individual atoms by using the Bond Dissociation Energy First, let’s look up the Bond Dissociation Energy for our non-metal, which is O2  495 KJ 3/2 O2(g)  30(g) Since the first coefficient of O2 is 3/2, we must multiply our Bond Dissociation Energy, 495, by it

Step Four Ionize the nonmetal atom by electron gain by using Electron Affinity Energy Now we use the dissociated non-metal from step three First we need to find out how many electrons O is gaining, which is 2 Then look up the value fore Electron Affinity Energy for O 737 KJ Since our coefficient for O is 3, we must multiply this number by 3 3O + 6e-  3O 2- To find the number of electrons, we multiply the number of electrons lost by O’s efficient

Step Five Now we need to add together the equations from steps two and four to form the crystalline lattice structure. This releases the lattice energy 2Ga 3+ + 3 O 2-  Ga2O3(s) Then we look up the lattice energy for Ga2O3, which is -12561 KJ

Finally! Now, to find the heat of reaction, we must add up the sum of each step! STEP ONE: 2 X 262 KJ STEP TWO: 2 X 2989 KJ STEP THREE: 3/2 X 495 STEP FOUR: 3 X 737 KJ STEP FIVE: -12561 SUM= -4839 KJ