molecular elements and compounds so when elements combine they could transfer electrons if that is the case if one of the atoms transfers electrons to another one what you end up with is an ionic compound what we're going to be talking about is that some atoms when they combine they don't like to lose their electrons so so they will combine with other atoms but they don't want to give up their electrons so what they end up doing is they will share their electrons and if atoms are sharing electrons they form what's called a covalent bond or a shared pair of electrons and you end up with these particles called molecules so molecules can be made from the same element if you take two or more of the same element on the periodic table take two of those atoms or three of those atoms or eight of those atoms whatever happens to be if it's all the same element and they come together as long as they're sharing electrons these would be called molecular elements so they are still only made up of one type of atom even though they're found in groups of more than one they could be pushed out in pairs like oxygen gas or they could be found in groups of eight like like sulfur is whatever the group is if it's only got one type of atom it is a molecular element as long as they're sharing electrons if it happens to be doing something other than sharing electrons it's not going to be a molecule so it has to be sharing electrons to be a molecule and molecules can either be made from all the same element or if they're made from different elements then you end up with a molecular because it's sharing electrons compound like water so the properties of these elements uh sorry the elements some of them are elements some other compounds this is a hugely diverse group of particles and so it's you can't really narrow down the properties there are some trends that you see but there's going to be lots and lots of exceptions as well so depending on what they are made of how those uh atoms are sharing electrons they can exhibit any one of the states depending on what the temperature is obviously but even at a given temperature you could end up with things that are molecules that are solids you can end up with things that are molecules that are gases and you can end up with molecules that are liquids as well all just at room temperature so it really depends on what type of particle you get molecules are very diverse they tend to have and again lots of exceptions but they tend to have a lower melting point definitely lower than ionic substances um and things like like metals and whatnot but generally speaking if you had to bet on it you'd say they probably are going to end up with a low melting point so there are a fair amount of gases and liquids that are molecular solids uh sorry molecular uh compounds that are not salt they are they're low melting points so they would be either a gas or a liquid um they tend to have low solubility so it again it completely depends on it so there are a lot that do have low solubility but some of them will dissolve it really depends on what and this is why we are going to be going into some of the particular types of molecules later also little conductivity this one's a pretty good bet if you have a a molecule um if you have a group of those molecules they're probably not going to conduct electricity so covalent bonding and again sometimes you'll see the term molecular bonding but the idea is that molecules are formed when atoms share electrons and and that sharing of electrons is called a covalent bond so they can prefer just covalent compounds but the the bond itself is a covalent bond molecules are held together by covalent bonds so non-metals these are the atoms and again you look on the top right hand side of the periodic table they don't like to lose their electrons so metals no problem they love losing their electrons but the non-metals don't want to lose their electrons they tend to have a they want to hang on those electrons they want to gain some more electrons so these will still want to become stable so they still want to end up with their full outer shell but they don't want to lose any electrons and they they they they're not going to give them away they will then in a lot of cases they'll end up sharing electrons if they combine with another non-metal so a shared pair of electrons again we refer to that as a covalent bond and this is what holds molecules together adam share electrons until they have a full outer shell so they are still trying to become stable but if they're a molecule they're doing it through the sharing of electrons not the transferring of electrons that ionic substances do so to practice with this we're going to try using a lose dot diagram to show the bonding between a phosphorus and a chlorine so again we start with our lewis dot diagram that is going to have your your symbol in the middle and then we're going to be putting the valence electrons around it so since phosphorus is in column 15 it has five valence electrons around it now chlorine is it's kind of light chlorine is in column 17 one two three four five six seven so it has seven valence electrons around it so these are both non-metals they do not want to give up their electrons so phosphorus isn't going to give any electrons to chlorine chlorine's not going to give any electrons phosphorus so if these are to form a molecule so we'd want to check to see if they do or not and yes they do and so if they are to form a molecule they're going to share their electrons with each other and so we can show this momentarily anyways by saying okay if phosphorus shares its electron with chlorine and so again it's going to be not transferring it over but it's going to be sharing that electron with chlorine and chlorine is going to be sharing its electron with phosphorus so now chlorine has one two three four five six seven electrons of its own plus it's counting this one as its eighth electron so chlorine has achieved its full outer shell it's complete octet it's stable it's happy it's done but you'll notice phosphorus now let's do that in a different color it has one two let's go here three four five of its own electrons and it's going to count this one that it's sharing with chlorine over here it's going to count it as its sixth electron that's the idea of sharing right you have access to the your own electron plus the one you're sharing with that that other atom so it has six electrons it is not yet stable so in order to get it to be stable it would have to combine with another chlorine so we'd have our let's see if we can get the color working here chlorine our second chlorine with one two three four i'm gonna go five six seven playing a little bit around with the placement so that i can show my sharing a little bit better so it has its seven electrons and then again let's do uh this one in yellow it's able to share these that's what i wanted these two electrons here so now it can count that other electron as phosphorus's seventh electron almost there now this chlorine is not going to do any more right because it is now stable it now has its own let's do that in green again one two three four five six seven and it's gonna count that one as its eighth electron so this chlorine is stable it's heavy it's got eight around it phosphorus though is still sitting at seven so we will need another chlorine around it and again when you react to things like phosphorus and chlorine you're going to have all sorts of them so the question is how many of them will it take to get the atoms stable and i'm going to put the seven electrons around chlorine like so and let's do this one in red and so it's going to be able to share let's do that share another pair here and again chlorine is going to have its stable eight and now phosphorus has this electron from the third chlorine as its eighth electron so now phosphorus is happy as well so the molecule that forms when phosphorus and chlorine react and again we're drawing chlorine atoms here it start off probably as a molecule but it end up as three chlorines to each phosphorus here the molecule would have one phosphorus and three chlorines and so we would show that in our formula we'd say okay there's one phosphorus and there are three of these chlorines being shared in there and we and we'd have our molecule um now this gets pretty messy so what we do to straighten things up a little bit is that we say okay this shared pair of electrons between let's say the phosphorus and that chlorine on the bottom here we're going to represent that with instead of drawing two dots with a circle around them we're going to draw a line so that line is a covalent bond so for each of these circled electrons here are the numbers and everything so we we did have two electrons one from each and we circled them to simplify things what we do is we just draw a line between the phosphorus and the chlorine and that line represents the shared pair of electrons so i'm going to go ahead and get rid of each of these and it's not a line and the electrons it is just the line so you end up with the each pair of electrons that is being shared between atoms represented by a single line it replaces the circle and the dots and that is the covalent bond so the line is used to represent a shared pair of electrons that's the covalent bond that is what holds a molecule together you can have multiple bonds and so imagine for oxygen gas now oxygen gas has the little bit smaller so we can fit some more things on here oxygen gas has the formula o2 so if we were to draw a a lewis dot diagram a single auction would have one two three four five i'm going to put the sixth one here so column 16 so it has six valence electrons so it needs to share two more now what you could do is you could say okay let's take another oxygen and we want to show the sharing with it so we could say okay let's circle these two electrons to show that those two oxygens will share those two electrons so that's one shared pair and then in order to get to eight they're going to share another pair of electrons so this oxygen gas molecule o2 is going to be made up of two oxygens and if they do that again let's do the count off here they've got one two three four five six of their own electrons that they started with plus seven eight that they're sharing with that other oxygen and they don't take them away from that oxygen so that that other oxygen still has access still is able to count those that seven and eight electron as their own as well so that first oxygen is stable it's good and again the same thing for the other one it's going to be stable as well now that's pretty messy so again what we do is we replace our circle and our two dots our shared pair of electrons and we just draw a line i'm going to replace this one as well and we keep the lines right between the atoms so instead of drawing continuously more and more like connecting one auction and another ox another action what you can do is you can get it to work out in a way that gives you in this case here two shared pairs of electrons in this case we've got a double bond this is covalently bonded two oxygen atoms covalently bonded together and it does it through two shared pairs and therefore it is a double bond with um nitrogen gas do this as our last example here so nitrogen gas again is in column 15 so it's going to have five valence electrons around it and let's say i didn't know the formula for nitrogen gas so i can say okay well one two three four so i need i know this this first nitrogen on the left here is gonna it's got five electrons it needs three more um and so what i could do is i could combine it with another nitrogen and i could share a pair of electrons like so now instead of adding a another nitrogen over here to share again with what i could should try to do is try filling it up with that original nitrogen first so i'm just putting electrons in there so they each have five they share one pair two pair three pair of electrons and now count them up original five plus three that are being shared each one has eight electrons around it they're both have full octets they're both stable they're both happy we're done let's clean this up a bit by replacing the circle and the two dots each of them there is three shared pairs so we just put three bonds between them and voila we have a triple bond