Main Group Elements: Boiling & Melting Points - Video Tutorials & Practice Problems
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1
concept
Boiling Point and Melting Point
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4m
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Here we're going to say that Boiling Point and Melting Point, abbreviated BP and MP respectively, are the energy used to change an element from a liquid to gas, when we're talking about boiling point, and from a solid to a liquid, when we're talking about melting point. Now, here we're gonna have 2 overall trends that we're looking at, and that's periodic periodic trend 1 and periodic trend 2. To follow these trends, we're going to split our periodic table into 2. In the first part, we're paying attention to groups 1a to 4a. Again, we're only concerned with our main group elements, so we're not going to pay attention to our transition metals. Here we're going to say, going from group 1 a to 4 a, the boiling point and melting point tend to increase, moving from the from left to right across the period and going up a group. So as we're heading towards this Carbon, this is the overall trend. We'd expect our melting point to increase, and our boiling point to increase. Now, let's look at the numbers. Here we have Lithium, its boiling point is 1347, and that's in degrees Celsius. Its melting point is a 180 degrees Celsius. Now, here, if we're looking, we can see that we're going from 671, 688, 766, 881 to 1347. We can see the general trend as we're going up this group, is it's increasing. And this is a general trend that we typically see also in groups 1A and 4A. Now, notice melting point, as we're going up, we can see those are generally increasing as well. If you are pretty observant, you'll see that, hey, why didn't you list any boiling point and melting points for group 2 a? Well, that's because within that group, because of numerous reasons, and again, we don't need to go delve into them directly, We're gonna have huge discrepancies. There's not gonna be an overall trend that's easy to see. We're gonna see that it can increase as we go up, and then decrease, and then go back up again. The pattern is not uniform, so we just take away our Boiling Point and Melting Points from this group. Now, here as we go to 3a, we see the overall trend, we'd also see that in these last 4 here, they don't have any melting points present. Because again, there are exceptions here that are arising because of differences in Bonding Type, as they're going from metallic to covalent network bonding, as atomic size is changing. So there's a lot of reasons why there isn't a uniform pattern for melting point for these 4. So we just ignore those as well. That's why the overall trend, when we pay attention to everything else, is increasing. Now if we look to group 5 a to 8 a, there's something you'll also notice. Typically, we see hydrogen here in group 1 a. But hydrogen can also exist or act as a halogen. It's one electron away from being, just like Helium. It has similar bonding characteristics of the Halogens. When it comes to Melting Point and Boiling Point, we can put it as part of group 7A because its overall pattern in terms of boiling point and melting point matches up. We're gonna say periodic trend 2, going from 5 a to 8 a, boiling point and melting point tend to decrease moving from left to right across a period, and going up a group. Here we have exceptions with these here. Their pattern is all over the place, so we don't worry about the overall trend for them. But once we take a look at all the other elements we can see that the overall trend is as we go up a group, we're going to have a decrease in Boiling Point and Melting Point. And as we go from Fluorine to Hydrogen, you see that that continues. We see that this overall decrease in Boiling Point and Melting Point. So that's why we're allowed to place Hydrogen here. Alright. So, from these two images, there's a lot that's being shown to us, but just remember, from groups 1 a to 4 a, our boiling point and melting point overall is increasing as we go up a group to the right. From group 5 a to 8 a, our overall trend for boiling point and melting point is that they decrease as we head towards the top right. So keep that in mind when asked to compare or observe the differences in boiling point and melting point for our main group elements.
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example
Main Group Elements: Boiling & Melting Points Example
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1m
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Under standard conditions, which element will be most easily vaporized? Now when we say most easily vaporized, that means which one becomes a gas most easily. And between boiling point and melting point, this means we're talking about boiling point, because that's where we go from a liquid to a gas. The one that's most easily changed into a gas would be the one with the lowest boiling point. Now, if we take a look at our options here, we have carbon, silicone, potassium, rubidium, and cesium. If you look at your periodic table, remember that carbon and silicone both can do covalent network bonding. This results in higher than normal boiling points and melting points, So those would not be our answers. If we look at potassium, rubidium, and caesium, looking on the periodic table, you'll see that they're all in group 1 a. So we have potassium, rubidium, and cesium. And remember, for groups 1a to 4a, as we go up and to the right of the periodic table, our boiling point increases. Here we're looking for the lowest boiling point, so that means the one lowest down, which would be cesium. So here our final answer would be option e.
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Problem
Problem
Which of the following Group 5A elements would be expected to have the highest melting point?
A
Nitrogen, N
B
Phosphorus, P
C
Oxygen, O
D
Antimony, Sb
E
Bismuth, Bi
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