Ch.9 - Bonding & Molecular StructureWorksheetSee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds
Chemical Bonds
Lattice Energy
Lattice Energy Application
Born Haber Cycle
Dipole Moment
Lewis Dot Structure
Octet Rule
Formal Charge
Resonance Structures
Additional Practice
Bond Energy

Lattice Energy is the energy required to combine gaseous ions into a solid, crystalline structure. 

Examining Lattice Energy

Concept #1: Understanding Exergonic & Endergonic Reactions 


Remember we said anytime we're forming a bond, it's described as a certain process. Every time we're making bonds, we're releasing energy. Every time we're releasing energy, it's an exergonic process. Exergonic processes form bonds are releasing energy. If that energy happens to be in the form of heat, then they get the name exothermic. Both are really saying the same thing. Exergonic is just the common thing for all forms of energy. Exothermic is if that particular energy originates as heat.

When dealing with the absorbing or releasing of energy in general then we use the terms endergonic & exergonic

Concept #2: Understanding Lattice Energy


We're going to say here lattice energy is the enthalpy change that occurs when one mole of ionic solid separates into its ions. We're going to say it tells us the strength of ionic interactions and has an influence on a lot of features – melting point, hardness, solubility, boiling point, freezing point.
A good example of lattice energy, the formula that we use for it, a good example would just be Li+ gaseous phase with F- gaseous phase combining to give us LiF solid. We're going to say here delta H would be 1050 kilojoules per mole. The lattice energy needed to break up lithium fluoride would be that much. This is how much energy would be required of us to break up lithium fluoride.
We're going to say here the formula for lattice energy or ionic bond energy can be broken down as this. We're going to say it equals the cation charge times the anion charge in absolute brackets. Because it’s absolute, we know that the anion charge will be negative, the cation charge will be positive. A negative times a positive gives me a negative answer. But because it's in absolute brackets, the answer overall will be positive. That's going to be divided by the cation radius plus the anion radius.
What do I mean by radius? I mean period number. I'm breaking down lattice energy in a much, much simpler way than your book or your professor normally would. In your book, it gives you a much complicated larger formula in order to figure out who has the largest lattice energy. You don’t really need to use that larger formula. You just need to focus on the fundamentals. This equation just breaks off all the complex part of the equation and gives you the most important part that you need to know. When it comes to lattice energy, you can use this basic form of the equation to always get the right answer.

Example #1: For each pair, choose the compound with the lower lattice energy.

a. BaO or MgO

b. LiCl  or  CaS

Practice: Choose the compound with the lower lattice energy.

Practice: Choose the compound with the higher lattice energy.