Main Group Elements: Density - Video Tutorials & Practice Problems
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1
concept
Phases
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3m
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Hey, everyone. So in this video, we're gonna take a look at the main group elements in terms of their density when looking at their phases. Now recall that at standard room temperature, which is around 25 °C and standard pressure, which is one atmosphere, the elements can exist under three states of matter. Now, we're gonna say in terms of density solids are more dense than liquids and liquids are more dense than gasses. Now, of course, in chemistry, there are exceptions, we know that hydrogen liquid, well, well, water liquid is more dense than water as a solid and it has to do with the bond expanding as it freezes because of hydrogen bonding. So water is an exception to this trend. But remember generally speaking, solids are more dense than liquids, which are more dense than gasses. Now, here, if we take a look at the periodic table, first of all, we're only concerned with periods 1 to 6 of the periodic table. The seventh row is made up of a lot of slab created elements, heavy elements, they're too unstable, too unpredictable. So we don't worry about them. Next, we're going to see that there's a lot of solids in terms of this periodic table, the ones that are in gray. Next, we have liquids and in terms of main group elements, only bromine is the one we're concerned with. When it comes to standard temperature, standard pressure, mercury is the other one with mercury is a transition metal. We're not worried about transition metals in terms of this topic. And then gasses, we can see those in red represent our gasses. Now, in addition to this, these elements exist in different forms within nature. Some of them exist as diatomic elements. These are elements that are stable in pairs when found in nature. And for us to remember the diatomic molecules, we say have no fear of ice, cold beer. Now, this does not condone any type of irresponsible drinking. This is just a helpful memory tool to help you recall the diatomic elements. So have hydrogen H two, no N two. Fear F two of is oxygen. 02 ice stands for in place of iodine. So that's I two. Cold Sea is chlorine cl two and B or B is Bromine, BR two, these are your diatomic elements. Now, if we take a look at this memory tool again, ice, what's the phase of ice? Ice represents a solid iodine under standard conditions is a solid. Then beer, what's the phase of beer? Beer is a liquid? And bromine under standard conditions is a liquid. So this memory tool help you remember the diatomic elements and also help you to remember the phases. All the other elements within this memory tool exist as gasses. Now, in addition to this, we have poly atomic elements, these are elements that are stable in numbers greater than two. So if we come here at the periodic table, we have phosphorus which naturally exists as P four sulfur, which is S eight and then selenium which is se eight. So these are the natural forms in which they exist in nature. The other elements, which we didn't talk about the main group elements, they exist together while they exist by themselves in nature as mono atomic elements. So that's why we didn't refer to them here. All right. So keep this in mind when it comes to density, the first thing we can look at is phases. So we're gonna say here, solids generally are more dense than liquids, which are more dense than gasses.
2
example
Main Group Elements: Density Example
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58s
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Here in this example question it says which of the following exists as a diatomic liquid at room temperature? All right. So remember diatomic means that exists in nature as a pair. So have no fear of ice cold beer. Bromine exists as a diatomic species. Tum does not sulfur exists as a poly atomic element. It exists as essay. So that wouldn't count. Chin is also diatomic as well as iodine. So the answer is gonna be either ad or e I remember in that same memory tool have no fear of ice cold beer. Beer exists as a liquid. B also stands in for Bromine. Bromine. Here is our diatomic liquid at room temperature, right? So remember that like handy memory tool to help us remember your diatomic elements and also you can rely on it to help you remember the phases of these different diatomic elements.
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Problem
Problem
Which of the following diatomic molecules would be expected to have the greatest density?
A
Chlorine
B
Selenium
C
Bromine
D
Iodine
E
Argon
4
concept
Periodic Trend
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1m
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Hey, everyone. So here we're going to take a look at the periodic trend when it comes to the density of main group elements. Here, we're going to say periodic trends are used when asked to compare elements of the same phase or when they're in the same group. Now, the periodic trend is density tends to decrease, going up a group. But across a period, there is no uniform trend. So if we take a look here at this periodic table, again, the seventh row, the seventh period is eliminated because it's too variable. All a lot of those elements are too heavy or manmade. So they're very unstable. So we're paying attention to rows 1 to 6. Now here going up a group, our density decreases, generally speaking, but as we go from left to right, either direction, it's too much variability. So we say that there's no uniform trend when, when we're looking across a period. Now, here you might notice we have purple for calcium and potassium here because they also represent some type of difference in the overall trend. Here. We're going to say they represent an exception. We're gonna say that potassium and calcium have lower densities than sodium and magnesium because they have higher volumes than expected. So here as we're going up, we should expect our densities to decrease. So we should have expected potassium and calcium to have a higher density than sodium and magnesium. But that's not the case. All you need to know on your part is that potassium and calcium just have larger than normal um volumes. This affects their overall density because remember density equals mass over volume. Anything beyond that is beyond the scope of this course. So don't worry about that. All right. So just keep in mind when we're looking up a group for the most part, our density is increasing. And remember the exception that we have here.
5
example
Main Group Elements: Density Example
Video duration:
50s
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Without any given values predict which the following would possess the greatest density. So here we have the periodic table and remember the general trend is as we head up a group, our density decreases. There is no uniform trend when we're going across a period though. So we won't pay attention to that. Now, here we have lithium, we have barium, we have magnesium beryllium and sodium. We can see that four of them are grouped closely together. And then on the very bottom, we have burial. Remember, the general trend is as we head up a group, our density decreases since barium is the furthest down we'd expect barium to have the greatest density out of the options that are given. That means that option B, barium would be our final answer.
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Problem
Problem
List the following elements in order of decreasing density under standard conditions:
a) Magnesium, Mg
b) Bromine, Br
c) Calcium, Ca
d) Barium, Ba
e) Hydrogen, H
A
d > a > c > b > e
B
d > c > a > e > b
C
e > b > c > a > d
D
e > c > b > d > a
E
a > c > b > e > c
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