this is a video lesson on classifying material we're going to classify material into four different categories heterogeneous mixture homogeneous solution homogeneous pure substance element homogeneous for substance compound and what i want you to focus on in helping you classify material are the words mixture solution element and compound now just to remind you as i said on the first day of class that when you look at any material in our world what makes material in our world or in our universe okay all material existing in our universe is comprised of one or more of these and that is the chemical elements now we can combine these and make different things we can make compounds we can make solutions and we can make mixtures but if it's just one of these by themselves of course you're looking at just a single element now in regards to the terminology that we have in classifying material difference between heterogeneous and homogeneous is whether or not our sample that we're trying to classify is uniform in mix in other words you can sample your material and if there's differences in the samples you would classify that material to be heterogeneous what you're looking at with heterogeneous material is actually a physical combination of two or more elements and or compounds that when they physically combine you'll see that they are not uniform throughout so you sample those two samples anywhere and you'll see differences so a really common example of this heterogeneous material would be oil plus water they don't mix and the liquid phase of your oil is different than the liquid phase of the water also another example of a solid heterogeneous material would be sand where in sand you have different sized particles you can see the difference in colors you can see the difference in textures and the different minerals other heterogeneous material would actually be fog because in fog you have a combination between solid well liquid particles plus a gas particles in the case of a fog being dispersed of a water vapor and then you can also have smog which is a solid and a gas so you'd have dirt particles suspended in the atmosphere and that would be heterogeneous now in the example of a homogeneous solution you're also looking at a physical combination but in this combination you'll see that your elements and or compounds form a material that is uniform throughout your sample and in liquid solutions you'll have a solute that's dissolved in a solvent the most common liquid solution is something like salt water where you have salt that will dissolve in water it will look clear and colorless but you do have two materials actually two compounds salt being a compound of sodium chloride and water of course is h2o and they mix uniformly but you can separate them by physical means you can evaporate out all the water and get your salt back you can also have a solid solution and a gas solution a solid solution is metal alloys and with metal alloys these are where we take some of the chemical elements that are metals so something like maybe a combination of copper and we melt this down and maybe put it with some silver or gold maybe strengthen up your gold jewelry not plating this but actually mixing these two together in the liquid state letting them solidify and you have a solid material that has mixed uniformly physically combined you can heat it back up separate the two metals and you would have yours your two metals back by physical means so metal alloys is probably the most common of solid homogeneous solutions the other type of homogeneous solution is a gas and what's interesting about gases is that we find that all gases if you combine two or more different gases they will always mix homogeneous and they will exist almost clear for the most well they will exist clear but they'll exist often colorless but there are some guesses that have color and when these two combine you can separate them by physical means one example of course would be our atmosphere like air as mentioned here and in air you have nitrogen and you have oxygen so we look at the physical properties of both these gases so the physical property of nitrogen in terms of its boiling point is negative 195.79 degrees celsius very cold material oxygen is also very cold its boiling point though is lower at negative 182.9 degrees celsius so what you're seeing is that you can condense because it's boiling point condensation point are the same you can condense these gases at different temperatures and separate them they did not chemically combine they just exist mixed uniformly in the atmosphere a good way to model this would be something like our um noble gases you know here i have a container of helium and then i add some nitrogen and argon and krypton and at the particulate size absolutely these look like i have a heterogeneous combination right here but if i were to zoom this out to a size to where i physically see gas i'm really not going to see these particles this is going to look clear and colorless to me just having these gases mixing uniformly okay so we can have physical combinations and the two physical combinations of material are either going to be homogeneous solution or heterogeneous mixture the difference is that heterogeneous is not a uniform mix where homogeneous is a uniform mix but again these materials in these two categories can be separated by physical means whether it means we're condensing it boiling it or filtering it or even using a magnet to separate iron filings from sand okay the last two but i already mentioned the element category but i'll mention it again are the homogeneous pure substance element and homogeneous pure substance compound now when we talk about this category of pure substance versus solutions not saying they're pure substances or heterogeneous saying that they're not pure substances is what makes it a pure substance is that the elements have chemically combined or the elements just exist as a single element comprised of their own atom so those are pure substances okay so elements if you have any one of just one of these you would classify your material as homogeneous pure substance element that's sort of the formal way to say element so if i have a sample of molybdenum okay a metal that was quite important during world war ii but anyway i had a sample of molybdenum i would classify my material to be an element if i have a sample say of even a gas like neon gas because neon is a pure element i would classify that compound or that that compound that substance to be a homogeneous pure substance element okay and then anything like cesium which is also a metal again classifying it to be an element so this is your resource to decide if your material would be classified as just a single element okay then we go to the next category which is the compound category and in this category what we are looking at is material that has chemically combined the elements have chemically combined to form compounds and what you're going to be looking for in deciding whether or not your compound your material is a compound is a chemical formula and we write chemical formulas in several different ways sometimes you'll come across a simple chemical formula like nacl and that chemical formula shows that n a and c l have chemically combined and we represent that as that chemical formula nacl which i will teach you in the future to name that is sodium chloride okay and then you can also see chemical formulas that contain different elements like carbon hydrogen and oxygen but you'll also see subscript numbers that indicate how many atoms of each of those elements are in the chemical compound so in the case of sucrose i have six carbon atoms 12 hydrogen atoms and six oxygen atoms that have chemically combined and we can model these several different ways one common way to model one type of compound is to show these molecular shapes these molecular geometries this being ammonia but don't know it don't ever guess on what your material would be classified as you may not know exactly what ammonia is comprised of but when you look it up what you're going to be looking for is that chemical compound