now let's say if we have two hydrogen atoms and if these two hydrogen atoms approach each other what's going to happen as you know they will react and form a covalent bond and a covalent bond is basically a bond where the electrons are being shared and so you can write the bond with a single bond or you could put two electrons between the hydrogen atoms and this concept makes sense if you think of electrons as particles but what happens if you begin to think of electrons as waves in that case a covalent bond is formed from the overlap of atomic orbitals and an orbital is a region where electrons are located where you have a high probability of finding an electron so let's think of electrons as waves if we have two waves in phase with each other what's going to happen they will interfere constructively to create a bigger wave with a larger amplitude so if you have two atoms approaching each other and if their orbitals are in phase with each other they will overlap constructively and so you're going to get a bond particularly a covalent bond because the electrons are being shared but what happens if the two waves are out of phase with each other well destructive interference will occur and instead of getting a bond you're going to get a node which is a region of zero electron density so basically the probability of finding an electron in its region is almost zero now according to valence bond theory a covalent bond is basically the sharing of electron density between two atoms as a result of the constructive interference of their atomic orbitals so let's consider hydrogen again hydrogen has one valence electron and electron configuration of hydrogen is 1s1 and s orbital has a spherical shape so this is going to be hydrogen with its spherical orbital and let's react it with another hydrogen atom so when these two get together their orbitals will overlap and you're going to get something that looks like this and so what we have in the middle is a covalent bond whenever two atomic orbitals overlap head to head it's known as a sigma bond all single bonds are sigma bonds so keep that in mind now what about when carbon mixes with hydrogen to create methane in order to do this carbon has to hybridize its atomic orbitals it has to create hybrid atomic orbitals and let's talk about the electron configuration of carbon it's 1s2 2s2 2p2 carbon has a total of six electrons two of those electrons in the first energy level are core electrons and they don't participate in most chemical reactions the other four in the highest energy level are known as a valence electrons and the valence electrons do participate in chemical reactions so let's draw an energy diagram for a free carbon atom so we have the 1s level the 2s level and the 2p sublevel so we have 2 electrons in the 1s level 2 and a 2s and 2 in the 2p sublevel this is the ground state electron configuration for carbon in the excited state an electron here could jump into this empty orbital if it's given energy right now we're going to just talk about the ground state electric configuration so during hybridization the 2s orbital and the 3 2p orbitals they're going to mix together to form a hybrid sp3 orbital so the 1s level is going to stay the same now we're mixing together four atomic orbitals and so we're going to get four hybrid orbitals and they're going to be degenerate orbitals of the same energy so if we mix an s and three p orbitals what are we going to get we're going to get a hybrid orbital called an sp3 orbital and because we mix four atomic orbitals we're going to get four sp3 orbitals now what should be the energy level of an sp3 orbital should it be close to the 2s level or to the 2p level what would you say because an sp3 orbital is produced from mixing 3p orbitals and 1s it has more p character than s character in fact it has 25 percent s character 75 percent peak character we have one s out of four atomic orbitals so one fourth is 25 percent we have three p orbitals out of four atomic orbitals so three-fourths is 75 and so because it's mostly p the energy level should be close to the two p sub level but a little bit lower than it so we get four hybrid orbitals these are known as degenerate orbitals because they have the same energy level as a result we're going to place all four electrons equally among those four orbitals of equal energy so the 1s level is unhybridized it was unaffected but these four atomic orbitals were hybridized into these four sp3 hybrid orbitals and hybridization is basically mixing if you mix water with orange juice you're gonna get something in the middle you can get a hybrid or let's say if you mix orange juice and milk you're gonna get something in between and that's what hybridization is you're just mixing atomic orbitals so if you mix s and p you get something that's in between s and p and so these are the four hybrid sp3 orbitals now let's go back to methane methane has four single bonds and so it has four sigma bonds and as we said before the carbon in methane has four sp3 hybrid orbitals highlighted in red and hydrogen can only form an s orbital because it has one electron in its 1s sublevel so let's say if you have a test question and it asks you what is the hybridization of the central carbon atom the hybridization of carbon is sp3 now how can we describe the hydrogen orbital we can say it's simply s and so if we want to describe the bond that connects carbon and hydrogen we could say it's a hybrid of s and sp3 those orbitals in red are sp3 hybridized and hydrogen is simply an s orbital so when you mix an s orbital with an sp3 orbital you could say it's a hybrid of s sp3 so that's how you could describe the hybridization of the bond and so anytime you have an overlap of atomic orbitals you're going to have a sigma bond so this whole thing is one sigma bond this is another and so methane has four sigma bonds or four single bonds or four covalent bonds you could describe it any of those three ways now let's talk about ethane c2h6 how many sigma bonds are in ethane as we said before a single bond is a sigma bond so one two three four five six seven so we have seven sigma bonds now what is the hybridization of the carbon atoms in ethane like methane the hybridization of carbon will be sp3 and each hydrogen atom will have an s orbital so to describe the ch bond once again we could say it's a hybrid of s and sp3 atomic orbitals now sometimes you need a simple way to quickly determine the hybridization of carbon so anytime you see a carbon attached to four atoms the hybridization is going to be sp3 if you add up the exponents one plus three is four now let's say if you see carbon attached to three atoms let's say this is x x y or something what do you think the hybridization of carbon is going to be it's going to be sp2 if you add up the exponents one plus two is three now let's say if carbon is attached to two elements let's say this is n and this is r or let's say if it's in this arrangement like in carbon dioxide the hybridization of carbon will be sp if you add one plus one you get two and for hydrogen you could describe the atomic orbital as s it's only going to be attached to one thing