hi this lecture is about atoms and molecules but this is something a little bit different than the previous lecture we're going to talk about how to read chemical formulas we're going to talk about which chemical elements are important to recognize immediately so in other words when you see that chemical symbol you know the name of that element and we're going to talk about chemical equations how to read a chemical equation let's start with talking about the elements for which you need to immediately recognize the symbol when you see them you do not need to memorize the entire periodic table so unless you're a chemistry major no reason to do that but there are some elements i want you to immediately recognize when you see them and the first of those is carbon remember all the elements are represented by a chemical symbol and they all start with a capital letter there could be a two letter abbreviation for that element and in that case the first letter is capitalized and the second does not we'll see an example of that in a moment so capital c that is carbon carbon is incredibly important to recognize you'll see it a lot this semester because it's the basis for all organic chemistry all organic molecules are made mostly of carbon and when we start talking about the big molecules that make up living organisms you're going to see carbon a lot h stands for hydrogen o is oxygen n is nitrogen p is phosphorus callie go ahead and tell you these are the ones you're going to see the most semester you'll sometimes see sulfur especially when we look at proteins you'll occasionally see sulfur this is the main list there are a few other ions that you should recognize because when we talk about transport across cell membrane and when we talk about ionic bonds you're going to see these elements so here's a good example of an element that has a two-letter abbreviation okay sodium couldn't use s because sulfur was using us so this is actually sodium so again capital a lower i'm sorry capital n lowercase a magnesium potassium potassium's letter k because phosphorus was using the p so again no need to memorize the entire periodic table but it is important to immediately recognize the most commonly used chemical symbols for this class and again carbon is the one you'll see the most now it's important to recognize how to read a chemical formula for a molecular compound and also how to read a chemical equation so i'm going to start with this one because you have seen this one if you have watched the video on covalent bonds this is the molecule methane it is an organic molecule and it's important to recognize what we mean when we write ch4 so first important to realize that this 4 is a subscript kind of hard to see that when i write it on the screen but that 4 is only telling you something about the hydrogen has nothing to do with the carbon also in chemistry we don't write a one so there's no one written in front of this molecule and there's no one written by the carbon but we assume if there's no number there it's a one so this is telling us that this methane molecule is made up of one carbon because there is no number after the carbon and four hydrogens and these are all bonded together to form this molecule let's look at another one let's look at water h2o most of you know the chemical formula for water again the subscript number is only telling you something about the hydrogen so this is telling us we have two hydrogens bonded to one oxygen again we don't write a one so we assume that since there's no number after the oxygen that that is one oxygen what if we had six h2o that big number six in front of the water is telling us we have six water molecules and if we count the total number of hydrogens and the total number of oxygens in those six water molecules we see that they're almost imaginary parentheses here so that 6 gets multiplied by everything after it so 6 times 2 that means we have 12 hydrogens making up these 6 water molecules and 6 times 1 6 oxygens again i know that's a one because there is a number there and if there is no number we assume that's a one we do not write the one in chemistry it's also very important to realize that the reason it's written this way the reason it's not written h1206 that would be something totally different and i'll show you that in a minute the reason it's written is six h2os is because here's what we really have it's telling us we have six of these and i am going to take the time to draw all six of them so i can really illustrate this point these are six separate water molecules they are not all connected through covalent bonds you're going to see when we talk about hydrogen bonds that they do actually connect with hydrogen bonds but that's not sharing electrons so we're not joining these through sharing of electrons we don't write them all together so if we had written h12o6 that would be a crazy imaginary molecule that doesn't exist but that would tell you you have 12 hydrogens bonded to 6 oxygens this is telling you something different okay there are 12 hydrogens total and there are six oxygens total but they are all separate h2o molecules and if you counted all the hydrogens you would see there are 12 and if you counted all the oxygens you would see there are six so that's telling you something very different than this this would tell you there are 12 hydrogens and six oxygens bonded together again that doesn't exist but just speaking hypothetically but this is telling you have six separate water molecules very important difference okay now let's look at a chemical equation let's look at chemistry happening and i'm going to give you the chemical equation for cellular respiration the most important chemical reactions that take place in your body so this general formula that i'm going to write is really just the general synopsis of what happens you're going to see when you learn about cellular respiration this is a very complex multi-step process this is a metabolic pathway it doesn't just happen all in one step but i like drawing this general chemical formula because it's a really good example of how to count the number of atoms on each side of the chemical equation and really seeing a good example of that okay i'm going to have to write this a little smaller because i have to fit the whole thing on here so c6h12o6 so these are all subscript numbers plus 602 and then an arrow very important 6 co2 plus six h2o okay the h2o you already know we just saw that this is glucose oxygen carbon dioxide and water a couple of things that are really really important about this this arrow is showing you the direction in which this chemical reaction is proceeding so this is the direction of the chemical reaction it's moving from left to right and it's moving from what we call reactants to what we call the products so the reactants are on the left side of the arrow and the products are on the right side of the arrow so in this reaction we would say glucose and oxygen are the reactants and carbon dioxide and water are the products if we went through and counted the number of each type of atom on the left side of the arrow it always has to equal the number on the right side and i'm going to show you exactly what i mean by that in a second but what's really amazing about chemical reactions is we're never creating matter and we are never destroying matter so matter is never created or destroyed in a chemical reaction this is a very important point in chemistry and it's often called the law of conservation oops of matter this is also going to be important from an energy standpoint when we really start looking at the energy involved in different chemical equations different chemical reactions in cellular respiration is going to be especially very very important looking at how we extract the energy from glucose and use that to drive chemical reactions in the cell very very important the reason it's important to realize that matter is never created or destroyed is it's important to recognize all we're doing in chemical reactions is usually breaking bonds taking those atoms and rearranging them to form something else but none of them go away okay none of them are lost we also don't bring anybody new into the party so if we look at the number of each type of atom on the left side of the arrow it needs to always equal what's on the right side of the arrow so let's look at who we have involved here carbon hydrogen and oxygen on the left side okay and on the right side we have carbon hydrogen and oxygen so already you can see there are no new players on the right side everybody who is on the left side is still on the right side nobody left nobody came in everybody's the same now we need to count the number of each and those need to be the same too and if they're not then you have to do something to balance it now i will go ahead and tell you we will not be balancing chemical equations in this class you'll be happy to know if you take a chemistry class you'll you will be balancing chemical equations but i want you to recognize all we're doing is breaking bonds and rearranging those same atoms to form something completely different and you can recognize that just looking at this equation glucose and oxygen very different from carbon dioxide and water but they are made of these exact same atoms that's pretty crazy to think about so let's do some counting this is a really good practice for reading these chemical formulas again subscript numbers only relate to what they follow so looking at glucose this six is only related to the carbon the 12 is only related to the hydrogen and the six is only related to the oxygen okay so that's telling us we have six carbons we have 12 hydrogens and we have six oxygens okay but that's just in the glucose we also have something else on the left side of that arrow and that is oxygen we have six o2s so that's saying we have six of these oxygen and it happens to be double bonded you wouldn't know that from looking at this but you would know that by drawing the electron configuration and figuring out how oxygen has to share with another oxygen that was the topic of the previous lecture on covalent bonds but you have six oxygens bonded together so you have six separate o2s which means you have 12 oxygens total so we're going to add 12 to this okay again where did i get 12 remember this is imaginary parentheses so that six gets multiplied by two in other words if we drew out all six of those o2s so i'm drawing this very sloppily so you can just get the point here so there's all six of my o2s that's 12 oxygens total so 6 plus 12 that means we have 18 oxygens on the left side of that arrow so in our reactants we have six carbons 12 hydrogens 18 oxygens let's count what's on the right side okay carbon dioxide again this six gets multiplied by everything after it so it's gonna be six times one that's six carbons six times two that's 12 hydrogens oops sorry goodness 6 carbons and 12 oxygens okay let's go on to water again imaginary parentheses here six times two and this is exactly how we did water before so you you should already be able to do this one because we just did it in the example above six times two that's 12 hydrogens okay and we're going to have some more oxygen here six times one that's six so that equals 18 also so 6 12 18 6 12 18. awesome so we have the exact same number and the exact same kind of atoms on the left side of the arrow as we have on the right side of the arrow very very important you will also be looking at compounds which come together through ionic bonding so if you see something like this and it's written together this is actually a compound and this is showing you that there's a sodium that was attracted to a chlorine and those are connected just through an attraction so this is more oops worse camera okay sodium and chlorine ionic bonding they have opposite charges so they're attracted to each other remember that when they're separate they have a charge which is written with a superscript so the sodium ion has a positive charge and the chlorine ion has a negative charge they're attracted to each other and when they're connected the positive one and the negative one cancel each other out remember that's different than the covalent bond so when we look at hydrogen bonded to hydrogen h2 that is shown as a line and that is a covalent bond this attraction between ions of opposite charge that's an ionic bond so that should review from the two bonding lectures and then of course real quickly going back up to the waters we drew if you haven't watched this yet this is a sneak preview if you have watched it it's review but remember neighboring water molecules are weakly attracted to each other through hydrogen bonding so all of these oxygens and hydrogens of neighboring water molecules are going to be weakly attracted to each other we show that with three dots and that is a hydrogen bond and i won't go into any more details about that in this lecture you should watch the hydrogen bond lecture for that okay that's all thanks