Lattice Energy - Video Tutorials & Practice Problems
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Lattice Energy is the estimate for the strength of ionic bonds.
Lattice Energy
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concept
Lattice Energy
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54s
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Here we're going to say that lattice formation energy is the change in energy when separated gaseous ions combine to form an ionic solid. So here we're gonna have sodium ion in its gaseous state, chloride ion in its gaseous state. Their opposite charges causes them to combine together to give us NaCl solid. Realize here that we're forming bonds, so it is an exothermic reaction. That's why delta h here is negative. Now, in an exothermic reaction, we release energy in order to create this new bond. And realize here that the more negative the lattice energy value, then the more exothermic the reaction becomes. So just remember, when we're dealing with lattice formation energy, we have gaseous ions as reactants and they combine together to give us a mole of an ionic solid.
Lattice Formation Energy involves an exothermic process where energy is released when gaseous ions combine into ionic solid.
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example
Lattice Energy Example 1
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45s
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So here it says the lattice formation of magnesium bromide is the energy change for which of the following processes. So remember, in a lattice formation reaction we have the ionic gases combining to form an ionic solid. So here, magnesium is in group 2 a, so it's 2+ charge, so this is good. Bromine is in group 7 a, so it's minus 1, so this is good. And then remember, they combine together to form an ionic solid, not a gas. So this is out. The answer the only answer that can work is option 3. None of the others work because they don't have ions to begin with that combine to form an ionic solid. So here our answer would be choice c.
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concept
Lattice Energy
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53s
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Under lattice formation energy, we talked about ions forming an ionic solid, but in lattice dissociation energy we're doing the opposite. Here, it's a change in energy of 1 mole of solid crystal as it's scattered into gaseous ions. So here, we would have our sodium chloride solid, and what would happen is we would split it up into its ions. Here, so gaseous sodium ion and gaseous chloride ion. This reaction is endothermic. Here we absorb energy in order to break the bond, in order to split it up into its ions. And because we're absorbing energy that's why delta h now is positive in terms of sign. Now, we're going to say here the more positive your lattice energy value, then the more endothermic the reaction will be.
Lattice Dissociation Energy involves an endothermic process where energy is absorbed when ionic solid is broken up into gaseous ions.
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example
Lattice Energy Example 2
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35s
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Here it says, which of the following reactions is associated with the lattice association of Lithium oxide? Now with lattice association, we start out with a solid ionic compound. So we're starting out with lithium oxide solid. That means that these 3 are out. And remember, it's an endothermic process, so we absorb energy to break this ionic solid into gaseous ions. So they have to have charges and they have to be in their gaseous state. That means option 4, which corresponds to choice d, would be the right answer.
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concept
Lattice Energy
Video duration:
52s
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Here we're gonna take a look at the lattice energy formula. We're gonna say by simplifying Coulomb's law, a general formula for lattice energy can be used to determine ionic bond strength. We're gonna say here the higher the lattice energy, then the stronger the ionic bond. Now the formula is lattice energy equals q one over times q two over r. This translates into the absolute value, so that means that answers always gonna be positive on top of the cation charge times the anion charge. And r here is radius, but when we simplify it, it means that we're adding the radius of the cation and the radius of the anion. Now realize here that the radius of the ion equals the period or row of the periodic table. So using this simplified lattice energy formula, we can compare different ionic bonds.
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example
Lattice Energy Example 3
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1m
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So here it's saying which compound possesses the strongest ionic bond. We have magnesium bromide versus potassium chloride. So for magnesium bromide, we break it up into its ions, so that breaks up into magnesium 2+ and brminus1. For the lattice energy, remember, it's their charges in absolute terms, so plus 2 times negative 1, divided by their period numbers added together. So magnesium, if you look on the periodic table, is in row 3, bromine is in row 4. So that is 2 7ths for its lattice energy. Potassium Chloride made up of Potassium ion and Chloride ion. Look and see whether you're on the periodic table. So remember we multiply their charges in absolute terms. Now look on the periodic table. Potassium is in the 4th row of the periodic table, so period 4. Chlorine is in the 3rd row. So here, lattice energy equals 1 7th. So if we compare the 2, we see that magnesium bromide has a larger lattice energy, and therefore it has a stronger ionic bond. Remember, the stronger your your lattice energy or higher your lattice energy, then the stronger your ionic bond will be.
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Problem
Problem
The lattice energy for ionic crystals decreases as the charge of the ions _____ and the size of the ions _____.
a) Increases, increases
b) Increases, decreases
c) Decreases, increases
d) Decreases, decreases
A
Increases, increases
B
Increases, decreases
C
Decreases, increases
D
Decreases, decreases
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concept
Lattice Energy
Video duration:
49s
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Now the lattice energy of an ionic solid has a direct impact on its physical properties. Here we can say recall, an increase in the lattice energy causes an increase in the strength of an ionic bond. And we can say here, as we increase the lattice energy, our ionic bond gets stronger, so the ions are held more tightly together. That would result in a higher boiling point, high melt higher melting point, but then a lower solubility. Solubility is how easily things break up and separate. But if you have a lot of lattice energy, you're held more together tightly, your ionic bond is stronger. So just remember the direct relationship between lattice energy, ionic strength, boiling point and melting point, but the inverse relationship lattice energy has to solubility.
LargerLattice Energy causes ionic bonds to be stronger. This in turn causes higher boiling and melting points, but lower solubility.
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example
Lattice Energy Example 4
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1m
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Here it says, choose the compound below that should have the highest melting point according to the ionic bonding model. So remember, highest melting point means highest lattice energy. When you break these all up into their ions based on the groups that they're found in, we'll be able to figure out the charge. Let's see here. Remember group number and their charges. Now we're gonna say lattice energy for all of them. In absolute brackets we have their charges multiplied together. On the bottom we're going to have the the periods that they're found in. So here all I'm doing is I'm inputting the charges for each one. So remember that's the first part we need for lattice energy. So here we're gonna multiply their charges in absolute terms. So for all of them the number will be positive. Now take the periods or rows that they're found on the periodic table and they're gonna go on the bottom but they're added together. So this would be 3 +2, this would be 3+2, 3+3. Now we're going to bring everything down. So this is 9 over 5, this is 1 over 5, this is 4 over 5, and finally this one here is 1 6th. The one with the largest lattice energy is aluminum nitride, and because of that it'll have the highest melting point. So just remember, the higher your lattice energy, the higher your melting point, the the higher your boiling point, and remember the lower your solubility. I know the question doesn't talk about boiling point and solubility, but it's important to remember these relationships.
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Problem
Problem
Which of the following compounds would you expect to have the highest boiling point?
a) MgCl2
b) SrO
c) SrCl2
d) CsI
e) LiBr
A
MgCl2
B
SrO
C
SrCl2
D
CsI
E
LiBr
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Problem
Problem
The solubilities of CaCrO4 and PbCrO4 in water at 25°C are approximately 0.111 g/L and 0.0905 g/L in H2O respectively. Based on this information, which compound do you think has the smaller lattice energy?