we will now look more in depth at chemical formulas the ways in which those atoms are bonded to each other and then how to name those compounds you will see chemical formulas communicated in a bunch of different ways the first is with something called a molecular formula which is just a list of element symbols and their subscripts so this is an example where you will see that subscript on the right side used to indicate how many atoms of each element are there so for n2 which was our example before there are two nitrogens ch4 is a molecular formula for a compound that has one carbon and four hydrogens and c2h4o2 has two carbons four hydrogens and two oxygens in that molecule you will also see structural formulas now this will come up not too much in this class eventually you will put together some simple structural formulas but i may give you a structural formula for things that are a little more complicated where i'm asking you to apply something but i i don't need you to come up with the connectivity all on your own so structural formulas give you the same information as the molecular formula plus they show how the atoms are connected so this is important because c2h4 could be acetic acid or methyl formate two different compounds just a different arrangement of the same number of each type of atom so in acetic acid if you kind of look at this from left to right we have a carbon that's attached to three hydrogens that carbon is also attached to another carbon the carbon on the right has a double bond to an oxygen a single bond to an oxygen and then that oxygen is connected to a hydrogen we'll go way more in depth about the double bond versus single bond but just so you know what the number of lines means in methyl formate we do start with a carbon with three hydrogens on the left but now that carbon is connected to an oxygen instead of another carbon and then the carbon on the right it still has a double bond to an oxygen but then it is connected directly to a hydrogen i'm going to break out the elements and compounds a little bit more so if you remember from our table in module one we had pure substances broken down into elements and compounds now within elements i can i finally am able to give you a little more information so we had helium as an example of an element helium would be an example of an atomic element so it means it exists as a single atom neon is another example of this so when you have a sample of just helium or just neon it is a bunch of individual atoms of helium or neon elements can also exist as molecules so oxygen is an example elemental oxygen exists as o2 which is two oxygen atoms connected to each other sulfur as an element exists as eight sulfur atoms connected to each other in phosphorus it's p4 so four phosphorus atoms connected to each other this is just how you would find it if you had a sample of elemental oxygen it would be a bunch of o2 molecules in that sample now there is a set of elements that are found as diatomics you should know this list there are a bunch of different acronyms out there to help you remember this list the one that i was taught is brinklehoff which is just a funny sounding word that is made up of these elements in a specific order to so if you can spell it you can write the elements out so that would be bromine iodine nitrogen chlorine hydrogen oxygen and fluorine where they all exist as diatomics so it's br2 i2 cl2 h2 o2 and f2 in the compound section you can have compounds that are molecular or ionic and so this is where we're going to get into different types of bonds and the only reason that it's important is that it determines the rules we use for naming so molecular compounds of which water h2o is an example are held together with covalent bonds and ionic compounds of which sodium chloride as an example are held together with ionic bonds so all atoms if they are connected to something else it is held together by some type of chemical bond the source of that bond is that they are either sharing electrons or transferring electrons and that is the difference between covalent and ionic covalent is sharing electrons ionic is transferring electrons and let's look at some better examples and a more in-depth definition an ionic bond occurs when you have a metal and a non-metal so when you look at the periodic table the things on the left side are metals and you'll you'll see that labeled the things on the right side are non-metals and there are very few non-metals compared to metals which if you go back to the periodic table section and you look at the legend that has kind of like other non-metals you'll see that most of the things labeled are metals right we had alkali metals alkaline earth metals a section we didn't talk about but the big one in the middle is transition metals and then the lanthanoids and actinoids are also metals tons of metals in the periodic table what happens here is that you get electron transfer but then once you have electron transfer you have a cation and an anion and what we know from what feels like maybe too long ago at this point is that if you have a positive and a negative charge those two things are attracted to each other so the bond is an electrostatic attraction between the positive and negative charges so in sodium chloride sodium becomes a cation so the one plus charge by giving its electron to chlorine which becomes the cl minus anion and then we have an attraction between those two charges now because this attraction occurs in 3d so in all three dimensions ionic compounds will form these kind of lattice structures so right i'm not going to ask you to draw a lot of structure or anything like that but it it becomes an important part of how ionic compounds behave so you should know that this happens so so one sodium add ion will attract chlorines all the way around it and one chlorine ion will attract sodiums all the way around it and so you just end up building out this lattice what that means is that if i take a piece of sodium chloride by it's really a bunch of sodiums and a bunch of chlorides all connected to each other the nacl is called the formula unit so when we have an ionic compound if you hear something referred to as a formula unit it's the smallest electrically neutral unit in an ionic compound in the example of calcium chloride calcium likes to form plus two cations and just to connect this back to our periodic properties everything else in the same group as calcium likes to form plus two cations that doesn't change what chlorine does chlorine still likes to form -1 anions so if i want to put these together in a way that makes an electrically neutral formula unit i have to use two chlorines for one calcium so cacl2 is the formula unit for calcium chloride a covalent bond exists between a non-metal and a nonmetal so just things on the right side of the periodic table and in a covalent bond the electrons are shared and these compounds exist as discrete molecules so not a lattice but in carbon dioxide so co2 i have individual co2 molecules in that sample you will also encounter polyatomic ions these are widely prevalent so they they exist all over the place and will be in so many of the compounds that we deal with what a polyatomic ion is is it's something that's held together with covalent bonds so within that polyatomic ion those atoms are held together with covalent bonds but it has an overall charge so as a whole it can be attracted to cations or anions depending on the charge in that polyatomic ion and form an ionic bond so bleach is a good example of this and bleach is sodium hypochlorite which is made up of a sodium one plus cation and this hypochlorite anion which is clo minus so sodium hypochlorite naclo is an ionic compound the ionic bond is between sodium and the polyatomic anion hypochlorite within the polyatomic anion the chlorine and oxygen are covalently bonded to each other this affects how naming and formulas are done and naming is so it's so important it's how we communicate about chemical contents so right i've got an example here of sodium hydrogen carbonate which is also sometimes called sodium bicarbonate because of course we have to have modern names and historical names and right i can type that out really easily or i could write a formula but they both mean the same thing which is that i have a sodium cation and a bicarbonate or you might call it hydrogen carbonate i'm fine with either and polyatomic anion that is in that molecule so the best way to work on naming is to practice it just takes a lot of practice there is an entire worksheet and we're going to do a ton of examples with this so check out the worksheet and check out i'm sure i'll make some example videos and if there are no example videos we will do a ton together in class