Main Group Elements: Density - Video Tutorials & Practice Problems
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concept
Phases
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Hey everyone. So in this video, we're going to 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 degrees Celsius, and standard pressure, which is 1 atmosphere, the elements can exist under 3 states of matter. Now we're gonna say in terms of density, solids are more dense than liquids, and liquids are more dense than gases. Now, of course, in chemistry there are exceptions. We know that hydrogen liquid well, water liquid is more dense than water as a solid, and it has to do with the bonds 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 gases. Now, 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 7th 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 word, but mercury is a transition metal. We're not worried about transition metals in terms of this topic. And then gases, we can see those in red represent our gases. 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 2. No, n 2. Fear, f 2. Of is oxygen o 2. Ice stands for in place of iodine, so that's I 2. Cold C is Chlorine Cl 2, and BRB is Bromine Br 2. 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 will help you remember the diatomic elements, and also help you to remember the phases. All the other elements within this memory tool exist as gases. Now, in addition to this we have polyatomic elements, these are elements that are stable in numbers greater than 2. So if we come here at the periodic table, we have Phosphorus which naturally exists as p 4, Sulfur which is s 8, and then Selenium which is SE 8. So these are the natural forms in which they exist in nature. The other elements which we didn't talk about, the mangrove elements, they exist together, well they exist by themselves in nature as monoatomic elements. So that's why we didn't refer to them here. Alright. 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 gases.
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example
Main Group Elements: Density Example
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Here in this example question it says, Which of the following exist as a diatomic liquid at room temperature? Alright. So remember, diatomic means they exist in nature as a pair. So have no fear of ice cold beer, Bromine exists as a diatomic species. Tellurium does not. Sulfur exists as a polyatomic element, it exists as Assay so that wouldn't count. Chlorine is also Diatomic as well as Iodine. So the answer is going to be either a, d, or e. Now 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
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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 7th row, the 7th period is eliminated because it's too variable. Although a lot of those elements are too heavy or man made, 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 see that there's no uniform trend when you 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 going to 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, 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. Alright. 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.
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example
Main Group Elements: Density Example
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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 4 of them are grouped closely together. And then at the very bottom we have Barium. 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: