 Let's explore coal and bonds where atoms share their electrons to fill their outer shell. Let's understand this using some examples. So let's start with oxygen. We know oxygen has an atomic number of eight. That means it has eight electrons in it. Now if we write down its atomic number, we have the two electrons in its first shell. That's the maximum it can carry. And then the remaining six electrons go in the next shell. And that's it. That means this shell now becomes the outer more shell. And notice this outer shell can hold a maximum of eight electrons, which means to fill it up. It needs oxygen needs two more electrons. How does it do that? Well, if it needs to is going to share two electrons with another oxygen atom. So let's see how. So here's we can draw a dot structure for this. And the way we do that is we first write the oxygen symbol. And then this is the atom. And then we're going to draw another oxygen over here. And this is going to be the atom of that. This represents whatever we draw over here will be shared electrons. And these are the electrons that are not shared. So let's look at first this oxygen. It has total six electrons that we're going to draw over here, but it can share two. So I'm going to put two here, because it's sharing those and out of six two are over here. So the remaining four will be can draw anywhere, but we usually like to draw it nicely. So we draw two here, two here. Look, the six electrons we have drawn two are shared the same thing we're going to do with this oxygen. It's going to share it's two electrons as well. And the remaining four we're going to draw over here. And now notice what has happened. If I ask you how many electrons does this oxygen has it has one, two, three, four, five, six, seven, eight, it has filled its outer shell. So it is happy. What about this oxygen one, two, three, four, five, six, seven, eight, it has filled its outer shell as well. So it is happy. So look, they have shared their electrons to fill the outer shell. This is a covalent bond. Now since they have shared two pair of electrons, we say that this oxygen forms a covalent bond with itself. And that's why oxygen in our atmosphere is mostly O2 because two oxygen molecules are covalently bonded to form a molecule. Let's now take another example. Let's take nitrogen, which has an atomic number seven. Why don't you pause the video and see if you can draw the dot structure of its covalent bond yourself. All right, let's try. So if it has atomic number seven, it means it has seven electrons. If you draw the atomic electronic configuration, two in the inner shell, five in the second shell, which means it needs how much to complete three. How does it do that? Well, if it needs three, it's going to share three. So let's draw the dot structure. So here is one nitrogen. And here is going to be our second nitrogen. The three that it wants to share, well, we'll draw it over here. And the remaining two from the outer shell, well, we can draw it anywhere we want. Remember, we only consider, we only show the electrons in the outer shell over here. The same is the case over here, this one, it's going to share three electrons. And the remaining two, we can draw it somewhere over here. And now let's count how many electrons does this nitrogen have? One, two, three, four, five, six, seven, eight, it's happy. And same is the case over here. It has fully filled outer shell. It's happy. And therefore it has formed a covalent bond. And since it has three pairs of electrons shared, we say that nitrogen forms a triple bond. So even nitrogen exists as an N2 covalently bonded molecule. Let's do one more hydrogen, which has an atomic number one. Can you write down the dot structure for its covalent bond? All right, since it has one electron, atomic number one means it has one electron, its atomic number atomic, sorry, electronic configuration will be one. That's it, right? Which means the first shell itself is its outer shell. And the first shell can accommodate two, which means it needs one more to have completely filled electron. So if it needs one, it's going to share one. So whatever electron it has that one electron, it's going to share it. So how are we going to draw? We're going to draw two hydrogen. And the electron that it has, well, it's going to share that. This is also going to share its electron. And now see, both are having two electrons. So they're both happy. And there we go. Now because it's sharing only one pair of electron, hydrogen has a single bond with itself. And therefore again, in the atmosphere, or usually hydrogen exists as H2 molecule.