 This video is about why elements bond together to create chemical compounds. To start with exploring this question, I will have to draw the periodic table of elements. If you want to talk about why elements form chemical bonds, we have to have a quick look at the modern periodic table. The elements are ordered by ascending atomic number or number of protons and are grouped in the columns so that each column, each group, has similar chemical characteristics. One of these groups has a very particular chemical characteristic. This group is called the noble gases. What is so special about those noble gases? They rarely form any bonds to build compounds. So one could choke that they are too noble to mingle with any other elements. They are always, or most of the time, staying alone by themselves. Like helium, neon, argon. You will find these atoms usually all alone, not in any compound. Now why is that so? The answer to that is a bit more complicated. It appears like these noble gases have more stable electron configuration than all the other elements. So if we talk about electron configuration, we have to talk about valence electrons. What are valence electrons? Those are the electrons that can participate in creating these chemical bonds. In our periodic table, it's quite simple to figure out the number of valence electrons. Group one has one valence electrons, group two has two. This one here has three, four, five, six, seven and eight for the noble gases except helium, which only has two. Now here in between for those metals, it's complicated. And down here, I don't want to talk about it. What I mean by it's complicated actually is that our simplified rather for Bohr atomic model is not able to explain what's going on here. We need a more advanced quantum-based atomic model to understand what's going on. So for the moment, we simply leave those out and we concentrate on what we can explain with the rather for Bohr atomic model. So just to make sure the numbers I wrote here are not the group numbers that you would usually find at this position in a periodic table. But what I wrote here is the number of valence electrons. Now as I said before, the noble gases, they tend to not form any compounds because their electron configuration of having eight valence electrons or two in the case of helium seem to be more stable. Now what's interesting is that all the other elements, what they try to do is to try to get the same electron configuration, which is called the octet rule. All the elements try to get the noble gas electron configuration. Depending on where these elements are in the periodic table, how they achieve noble gas configuration the easiest way is different. For example, all those that are close to the right side, the easiest way for them to get noble gas configuration is to get more valence electrons. So if your nitrogen, you already have five, you want to have one, two, three more to have the same electron configuration as neon. So those elements that are in this corner here, more to the right, that can get noble gas electron configuration by getting more electrons are called the non-methods. Then on the other side, like everything down here, it is simpler to lose electrons. So if lithium, for example, gives up one valence electron, then it will appear and look like the electron configuration of helium and noble gas, so it will be happy. So all of those down here, the metals, they tend to lose valence electrons to obtain the noble gas electron configuration. The exception here is hydrogen, which we write here, but it's actually not a metal, it's a non-metal, and it will try to gain valence electron in order to appear like helium. In between, you have a couple of elements, they're having both options. For them, it's about the same to gain electrons or to lose electrons, so they can act like non-methods or they can act like metals depending on the situation they're in. Now the question is, how do the metals and non-methods do this? In the easiest cases, if a metal gets together with a non-metal, the metal, if up some electrons, the electrons transfer to the non-metal and we create what's called an ionic bond. Door number two is, if a non-metal gets together with another non-metal, so none of them wants to get rid of their electrons, both want more. So what they can do, they can share electrons between each other and that way form what we call a covalent bond and in this way get noble gas electron configuration. Now the third option is metals getting together with other metals, so none of them wants electrons, they all want to get rid of electrons. So what they do, they push their electrons a bit further away in what we call the electron cloud. So these electrons are not directly attached to the metal anymore, which have the interesting effect that they can move quite easily throughout the substance, which is why usually metals are good electric conductors. That's a quick overview of why elements bond to form compounds. Quick and short answer is they form compounds in order to achieve the electron configuration of the noble gases.