welcome this is mr. W and this is basic chemistry for biology students the subject of this video covalent bonds and structural formulas let's start with a bit of review our last video focused on ionic bonding we started with the idea that in accordance with the octet rule atoms are only happy if their outer orbitals are full to capacity with two electrons in the first orbital eight in the second and eight and the third ionic bonding happens when unhappy atoms team up with one another and exchange electrons in a way that fills their outer orbitals as they do this these unhappy atoms become charged ions that stick together and that attraction between oppositely charged ions is an ionic bond ions and ionic bonding are crucial in biology but the molecules that make up living things like DNA which stores and transmits genetic information are held together primarily by a second type of bond the covalent bond we'll start by looking at the structure of hydrogen gas or H 2 H 2 hydrogen is the simplest and most common molecule in the universe how does it form well it's all about atomic happiness a hydrogen atom has one proton and one electron as a single atom hydrogen is unhappy why because the first energy level has a capacity of two electrons and hydrogen with one electron only has one electron in that first orbital with one electron hydrogen is simply unfulfilled by sharing its electrons with another hydrogen atom hydrogen can achieve an atomic version of happiness here's what it looks like when two hydrogen atoms share their two electrons this sharing holds the two atoms together and that is exactly what a covalent bond is it's when atoms are bound together by one or more pairs of shared electrons let's look at a slightly more complex molecule the molecule is methane also known as natural gas its formula is ch4 notice that there's no number next to that see that indicates that there's one carbon bonded to four hydrogen atoms all around our planet methane is a very important fuel source and it's also very significantly involved in climate change a topic that I've addressed in a series of music videos here's methane burning on my kitchen stove methane's formula as we just said is ch4 so how does it form you know that carbon has six protons six neutrons and six electrons following the octet we will be put the first two electrons in the first orbital that's fine but that leaves four electrons in the second orbital and that makes carbon an unhappy atom hydrogen as we've discussed is also an unhappy atom because it has one electron rather than two in its outer orbital knowing that the chemical formula of methane is ch4 one carbon and four hydrogen's I'll bet you can figure out how to draw it so what I'd like you to do is click pause give it a try and when you're ready click play to see if you got the answer correct here's methane ch4 one molecule that's making five atoms happy we'll start with carbon because it's sharing electrons with four hydrogen's carbon now has eight electrons in its outer energy level making it happy and because each hydrogen is sharing an electron with carbon each hydrogen has two electrons in its outer orbital a perfect match we saw when we looked at a hydrogen molecule that hydrogen can share electrons with itself well carbon can do the same thing and that's actually critically important for the molecules of life but knowing that carbon can do that here's a little challenge see if you can figure out how to draw ethane c2h6 it's another kind of natural gas pause the video give it a try and then click play to see if you got it right here's ethane c2h6 each carbon is bonded to three hydrogen's and the two carbons are bonded to one another arranged like this each hydrogen has two electrons orbiting its outer shell so hydrogen is happy each carbon has eight electrons orbiting its outer shell each carbon is happy one kyoool ate happy Adams is in covalent bonding fantastic so far we met three covalently bonded molecules hydrogen h2 methane and ethane and now that we understand how covalently bonded molecules work that they're held together by shared hairs and electrons we're going to start using a different way of representing these molecules what we'll use is called a structural formula you'll use this type of formula throughout the rest of your studies of biology there are two rules for drawing structural formulas but first instead of drawing out the entire atom with its nucleus and electrons and all the orbitals you're just going to use a chemical symbol to represent that out secondly you'll represent each shared pair of electrons with a - so here's the structural formula for a hydrogen molecule I put the orbital model right next to it so you can compare the two and see how that you will eight here's the structural formula of methane with an orbital model for comparison if you're getting this you should be ready for this challenge we've already looked at the structure of ethane c2h6 so now your job is to draw the structural formula pause the video give it a try then click play to see if you've got a right here's ethics structural formula it shows how each carbon is sharing electrons with three hydrogen's and how each carbon shares a pair of electrons with the other carbon the three molecules that we've discussed so far hydrogen methane and ethane are held together by single covalent bonds that means that the atoms inside these molecules are connected by a single shared pair of electrons which we represent with that single - sometimes the atoms in a molecule are held together by double covalent bonds these double bonds involve two shared pairs of electrons you can see this in the molecule ethylene c2h4 yet another kind of natural gas ethylene is used as a starting point in many industrial processes and it's used for making hundreds of different types of plastics and textiles when you study plants you'll meet ethylene again because it's also a plant hormone that plays a key role in the ripening of fruits here's an orbital model of ethylene along with its structural formula the carbon atoms in ethylene are sharing two pairs of electrons with one another those two shared pairs make up a double bond and we represent that with the double dash at the same time each carbon is sharing a single pair of electrons with each hydrogen and we show that with a single dash the result six happy atoms each with a complete outer orbital and you can see the double bond between the two carbons oxygen o2 the gas that we breathe in with every breath is another double bonded molecule as you can see the two oxygens share two pairs of electrons so as a result each oxygen now has eight electrons in its outer orbital making it happy we represent that double bond in the structural formula with the double - even triple bonds are possible in this compound c2h2 acetylene the fuel that's used in an acetylene torch the two carbons have single bonds connecting them to the hydrogen's and triple bonds connecting them to one another that triple bond you can see involves three shared pairs of electrons it's impossible to overstate the importance of covalently bonded molecules in biology they are simply the bonds that hold the molecules of life together you're made of covalently bonded molecules you inhale and exhale covalently bonded molecules you eat covalently bonded molecules your muscle fat skin genes they're all covalently bonded molecules at this point in the series you know what to do in order to learn this stuff you've got to interact with it and I've set up those interactions over at my website science music videos comm so go to my website do the flashcards do the multiple-choice quizzes do the other activities and that's how you're really going to come to understand how covalent bonds and structural formulas work I also want as always to invite you to leave me comments leave me questions either on YouTube or science music videos and if you can't think of a comment or a question I've got one for you it's going to appeal to the poet scientist inside of you here's the question this is not more like a covalent bond or more like an ionic bond leave a comment explaining what you think I'd love to hear it and I'll see you at the next video