Consider the following compounds: KF, NaF, and RbCl. Answer the following questions based on
expected periodic trends:
(a) Which is expected to have the shortest ionic bonds?
(b) Which is expected to have the highest lattice energy?
(c) Which is expected to have the lowest melting point?
a=Naf
b=Naf
C=RbCl
Agree or disagree?
I didn't look this up but you can Google them and find out.
To determine the answers to these questions based on expected periodic trends, we need to consider the following factors: the size of the ions and the charge of the ions. Let's break down each question and analyze the expected trends:
(a) Which is expected to have the shortest ionic bonds?
The size of the ions plays a significant role in determining the length of the ionic bond. Generally, smaller ions tend to form shorter bonds. In this case, comparing KF, NaF, and RbCl, we can observe that K (potassium) has the smallest atomic radius, followed by Na (sodium), and then Rb (rubidium).
Now, since we are dealing with monovalent ions (with a +1 charge), the smaller the cation (positive ion), the closer it can get to the anion (negative ion), resulting in a shorter ionic bond.
So, the expected answer is: KF is expected to have the shortest ionic bond.
(b) Which is expected to have the highest lattice energy?
Lattice energy is the energy released when ions come together to form a crystal lattice. It is influenced by both the charge and size of the ions. Generally, higher lattice energy is observed when ions have a higher charge and when ions are smaller.
In this case, considering KF, NaF, and RbCl, all the compounds have monovalent ions, so the charge factor remains the same. However, the smaller the ions, the higher the lattice energy.
As we established earlier, K (potassium) has the smallest atomic radius, followed by Na (sodium), and then Rb (rubidium). Consequently, KF is expected to have the highest lattice energy.
(c) Which is expected to have the lowest melting point?
The melting point of an ionic compound is generally higher when the forces holding the ions together are stronger, such as when there are larger charges on the ions or the ions are smaller in size.
Considering KF, NaF, and RbCl, all the compounds have monovalent ions, so the charge factor remains the same. However, as we established earlier, Rb (rubidium) has the largest atomic radius, followed by Na (sodium), and then K (potassium).
Larger ions tend to have weaker forces between them, resulting in a lower melting point. Therefore, RbCl is expected to have the lowest melting point.
In conclusion:
(a) KF is expected to have the shortest ionic bond - Agree.
(b) KF is expected to have the highest lattice energy - Disagree (It should be NaF, as Na is smaller than K).
(c) RbCl is expected to have the lowest melting point - Agree.