hi everyone welcome back to the next chemistry lecture we have been discussing biologically important bonds in living organisms most of the strong chemical bonds are covalent we've discussed the polar covalent nonpolar covalent bonds and these covalent bonds link atoms to form a cell's molecules biologically important weak bonds also include the ionic bonds that we talked about ionic bonds are weak in water think about if you put salt in a glass of water stir it up the water is able to break those ionic bonds and you end up with a glass of salt water it's water molecules sodium ions and chloride ions ions or electrolytes are very important to the body they're important with respect to even neuron signaling right your nerve nerve conduction sodium is really important in nerve conduction potassium plays a really important role in conducting cells signaling and calcium ions are really important in muscle contraction and when you go on to take anatomy and physiology you'll be going into the physiological mechanisms and how these ions play a role the last type of weak bond that we're going to discuss one of the most important types of weak bonds is the hydrogen bond hydrogen bonds are important in three dimensional structure of proteins for example they're very important in the structure of dna hydrogen bonds are the bonds that hold together those nitrogenous bases that we talked about pause the recording and in your notebook write down the nitrogenous bases that we discussed and which ones pair up together if you need to look back in your notes go ahead and look back in your notes but please write down in your notebooks the four nitrogenous bases and which two pair together so it's hydrogen bonding that holds those base pairs together to look at hydrogen bonds we're going to talk about water molecules to illustrate this type of bonding the hydrogen atoms of a water molecule are attached to oxygen by polar covalent bonds so we want to remember there's a difference between our polar covalent bonds and hydrogen bonding in our image on the left is one water molecule one h2o molecule the oxygen and the hydrogen this bond is our polar covalent bond this oxygen and hydrogen this is a polar covalent bond in the image on the right we have a water molecule here in the center these oxygen and hydrogen bonds are polar covalent and we have our partial positive charges on our hydrogen and our partial negative charge on the oxygen when water molecules approach each other the partial positive charge on hydrogen attracts the partial negative charge on oxygen the weak electrical interaction is an example of hydrogen of a hydrogen bond an attraction between a hydrogen atom with a partial positive charge and another atom usually oxygen or nitrogen with a partial negative charge these dotted lines represent the hydrogen bonding you can see this partial negative charge on this oxygen has an attraction to the partial positive charge of this hydrogen over here on this water molecule we also have a partial positive charge here on this hydrogen and it is attracted to the partially negative charge on this oxygen atom from this water molecule so you want to keep in mind when you're looking at a water molecule understand the difference between the polar covalent bonding that's occurring in the water molecule and the hydrogen bonds that occur between water molecules hydrogen bonds are weak bonds they're weaker than covalent bonds hydrogen bonds are only about five percent of the strength of a covalent bond because of hydrogen bonding this allows water to remain as a liquid over a wide range of temperatures it also causes surface tension and we'll talk about that shortly each water molecule can bond make up to four bonds with other water molecules in this image this water molecule is bonded to three other water molecules but it does have the ability to make one more hydrogen bond the next two slides are just everything we've already discussed with the pictures in word form so i'll read them but again we have looked at this and already discussed this with the pictures so visually if you learn well by sentences this is just describing what we've talked about because of the polar bonds and the wide v shape of the molecule water is a polar molecule it has an unequal distribution of charges this is our polar covalent bonding therefore water is a polar molecule it's the partial positive charge that allows each hydrogen to be attracted to a nearby atom that has a partial negative charge weak hydrogen bonds form between water molecules each hydrogen atom of a water molecule can form a hydrogen bond with a nearby partially negative oxygen atom of another water molecule the negative oxygen pole of a water molecule can form hydrogen bonds to two hydrogen atoms therefore this means that each water molecule can hydrogen bond to as many as four partners let's watch a brief animation of our water molecules forming those hydrogen bonds another really interesting aspect of hydrogen bonding with water is that water is the only substance on earth that can be found in all three phases water can be found as a solid right as ice a liquid and a gas how does a water molecule form here you're looking at a chemical reaction and you have two hydrogen molecules two h2 molecules and one oxygen molecule these molecules are going to combine interact they get rearranged all of the atoms rearrange and you form two water molecules let me just bring that up so that you can see it so again you have two h2 molecules these are each a hydrogen this is one h2 molecule this is the second h2 molecule right here and you have one oxygen molecule so all total when we look at the atoms there are four hydrogen atoms here and there are two oxygen atoms here to form our water when these molecules are interacting we end up with two water molecules we still have a total of four hydrogen atoms and we still have a total of two oxygen atoms so two h2 molecules plus one oxygen molecule yields two water molecules the formation of water from hydrogen and oxygen is an example of a chemical reaction the reactants h2 and o2 are converted to water h2o which is our product chemical reactions do not create or destroy matter chemical reactions only rearrange matter again you your products have the same number of atoms that you started with in the reactants in photosynthesis energy in sunlight is transformed to chemical energy by converting the bonds and carbon dioxide to the bonds of a carbohydrate or glucose so here we have our carbon dioxide and previously i had to draw this molecule you were supposed to look it up you were having um determining what the bonds look like and the structure so the the bonds in the carbon and oxygen here get converted into this is glucose you don't need to memorize the photosynthesis reaction per se i do want you to be able to recognize glucose if you see c6h12o6 you should be thinking glucose what you will need to memorize or have a really good recognition is cellular respiration and if you notice cellular respiration is the photosynthesis equation backwards we have oxygen and glucose right here's our oxygen and glucose that's our reactants for respiration and this will yield carbon dioxide water and energy these are the products in respiration but they are the reactants in photosynthesis so these are just the inverse of one another so again familiar familiarize yourself with that c6h12o6 as soon as you see that you want to think of glucose now if you're taking a chemistry class you're sitting there going man that's not exactly how we were taught in chemistry we're really simplifying it here by saying co2 water and sunlight is yielding glucose sugar and oxygen but in chemistry you know that this is actually a ratio of carbon hydrogen and oxygen so again we're simplifying it and that's okay just know that use this ratio for our particular class six carbons 12 hydrogens and six oxygens it's a one to two to one ratio for those specific elements so again we're looking at a chemical reaction here carbon dioxide from the air is reacting with water the energy from the sun is what's powering that conversion of these reactants to the products glucose and oxygen and to really drive home this idea of this reaction that we're not creating anything we're just rearranging these molecules there are six carbon dioxide molecules just like in our previous equation we had two h2 molecules the six tells you how many molecules of this particular molecule that you have so you would have six of these one two three four five six co2 molecules you also have six water molecules so these are the reactants all total out of all the reactants you have a total of six carbons here you have a total of 12 hydrogens there are six h2 molecules meaning two times six there are 12 hydrogens if you come over here and look at glucose or you can look at it here these are both the same you can see there are still in the products only six carbons and there are still only 12 hydrogens you haven't created anything you haven't lost anything as far as the number total number of oxygens in six water molecules you would have a total if you drew them all out you would see that there are six oxygens and in the co2 out of all the six co2 or six carbon dioxide molecules you would be able to count that there are 12 oxygen atoms if you take these 12 oxygen atoms and you add these six oxygen atoms the total number of oxygen that you have in the reactants is 18. if you come over here and look at your products and you have six molecules of o2 so that's 12 oxygens and in your one glucose molecule you have six oxygens so six oxygens in your glucose molecule plus the 12 oxygens in your 602 molecules you you would be able to count a total of 18 oxygens in the products this matches the 18 of your reactants so again we're just re reinforcing this fact here that chemical reactions don't create or destroy matter it just simply rearranges it and again really familiarize yourself with if you see c6h12 i want you just to in your head automatically say glucose or sugar something of that nature all right we are going to conclude this recording here and we will pick up the next lecture with our unique and interesting properties of water