all right let's look at covalent bonds they are a strong bond between two nonmetals on the periodic table most of things to this side are metals and over here most of these are nonmetals if you remember sponge that is the six most common elements in living things they all exist over here they are all non metals hydrogen is the exception to the metal rule it is over here on the left hand side so all of our sponge elements are nonmetals and therefore old form covalent bonds and the other reason that it makes sense that elements found in living things form these covalent bonds remember I said these are strong they're the equivalent of superglue and they don't fall apart in water and that was the difference ionic bonds do fall apart in water and all life requires water to exist so if these bonds came apart in water they wouldn't work to form the molecules found in living things okay covalent bonds are going to be the result of the sharing of electrons between atoms why are these animals going to be willing to share electrons because by doing this both atoms in the bond will get a full shell of valence electrons right and they aren't electrons of those outer shell electrons so Kobe on it like cohabiting right KO together valence as in valence electron sharing the arms electron and again atoms share electrons to acquire to gain a full set of valence electrons there's electrons in the outermost shell and quick review right when we talk about the shells that we're likely to find electrons in the first shell closest to the nucleus holds how many electrons again yep can fill up the two after that it fills up second shell will hold eight and the third shell holds eight right and you just have to memorize that so make sure that you know that it makes sense that the innermost shell holds fewer electrons because there's less space in it we can use some representation on paper and this is sort of a form of Lewis dot structure where we're going to represent valence electrons as little dots around the chemical symbol and this isn't popular structure hopefully you'll learn that later there's a number of different ways you can draw this and if you have a different way that's just fine so at the middle of the atom we're going to represent the atom with the chemical symbol for that atom it can full symbol and then we're going to represent all the arms electrons by dots into the dot structure right so just the electrons in the outermost shell let's start with something easy let's start with hydrogen so the periodic table entry for hydrogen looks like this and take a second to work out how many electrons you should find in a typical hydrogen atom an uncharged hydrogen atom so hopefully you came up with one electron if you didn't or you didn't try to work that out please please go back and review because if you if you can't do it now think about trying to do it on a test when you're under pressure and it won't go so well right that's that's why we practice things okay using using the Royal we there okay so a typical hydrogen atom has one electron and the first shell will hold up the two so that one electron is going to be in the outermost shell that is the first shell and so I can draw an edge with the dot next to it so if this hydrogen happy fulfilled in an atom no right because it wants to have a full outer shell what if it found a buddy and let's start with just another hydrogen atom right so here's my second hydrogen atom with its electron represented here and said hey why don't we share our electrons then everybody gets a full outer shell and so the hydrogen atom on the left of hey sometimes I get to use your electron and the hydrogen atom on the right says yeah okay if sometimes I get to use your electron everybody better give the same number electrons with therefore looking to share and if I now count the number of electrons within both of these circles the green circle on the blue circle the green circle which represents the electrons that this hydrogen atom has has one two electrons right the one that it has and the one that it's sharing so it has a full outer shell and if you look at the blue circle same situation these two electrons will also partially orbit this hydrogen atom and therefore it gets to and they do remember the electrons are buzzing all over the place so these two electrons will be kind of hanging out around here some and then they're going to go hang it up around here some and so everybody involved get these two electrons at least part of the time and then we further represent these shared electrons by drawing a little click in between the two atoms involved this represents right it's not actually a stick it represents two shared electrons or a pair of shared electrons to share an electron and it also represents a chemical bond of covalent bond we do not see lines in between ionic bonds so it represents a covalent bond between these two hydrogen atoms and then we can even further simplify it and say I have a molecule of hydrogen so a molecule is what is formed when more than one atom come together with covalent bond so this is a hydrogen molecule 1h on its own as a hydrogen atom and most of the things we see in biological samples with the exception of salt and electrolytes are molecules biological molecules proteins are molecules are held together by these strong covalent bonds covalent bonds we can have different numbers of covalent bonds so let's look at another example let's look at oxygen and can I do something let's let's look at yeah let's look at oxygen so it's atomic numbers eight masses fifteen point nine nine nine and so you're calculating how many electrons does it have and then once you do that you say okay well how many of those electrons are beyond electrons negatively charged electron so hopefully beats for the number of electron they aren't electrons or electrons in the outermost shell we're going to start by filling that first shell first so the first shell will hold 2 so 8 minus 2 electrons which fit into that first shell leaving with six electrons so we have six valence electrons because the second shell will hold up to eight and I can represent this with little dots six dots around one oxygen is this oxygen atom happy right happy doesn't have feelings no right it wants to have eight how many more electrons need to have eight and needs two more so what if it finds another oxygen atom for example and instead of just sharing one electron pair between them they share two electron pairs right so the oxygen on the left gets to borrow two occasionally from the oxygen on the right and the oxygen on the right gets to borrow two occasionally from the oxygen on the left so if I count the number of dots which represent electrons inside the green circle I've got one two three four five six seven eight right full outer shell same deal with the blue circle one two three four five six seven eight everybody get a full set of electrons by sharing and I can represent those shared electrons by two lines right so we hear these this represents a double covalent bond as a stronger even than a single covalent bond and it represents in this case for shared electrons or shared electron you can also have a triple covalent bond and the place that we would do that is say between two nitrogen's and I would you know take a second and work out why that you'd see this and this would be a triple covalent bond we don't see any more than that this triple covalent bond is usually hard to break there's a lot of nitrogen on our planet it is mostly in the atmosphere so you know 70% of the air that we breathe is nitrogen gas and all living things need nitrogen and it's really hard to break up nitrogen gas to use that there's only a few things they can do that there are bacteria that usually are associated with plant roots that allow certain plants like beans to be able to get nitrogen and that's why beans are considered really good for your soil because they provide nitrogen to that soil that other plants could later use but other plants can't just acquire nitrogen from the atmosphere like that so those are covalent bonds what I would do is do a few more practice problems about like hey how many covalent bonds should carbon form because carbon is a maximum building block you can decide how many covalent bonds phosphorus or sulfur should form or even something like silicon how many how many coal gram bonds these guys should form do you do some practice