oh this is just an image of the previous topic where you see two cellulose chains and the cellulose chains are forming hydrogen bonds with each other I did mention that oxygen has a partially negative charge and hydrogen has a partially positive charge you want to talk a little bit more about this today so but before we talk about that let's just look at water molecules now water if you remember is just basically H2O where it's made up of two hydrogen atoms covalently linked to one oxygen atom now for that to happen the hydrogen will have to share one of its electron with oxygen the other hydrogen will also have to share one of its electron with oxygen and the oxygen right now the valence shell will have a total of eight electrons which makes it stable hence this is how the covalent bond forms between two atoms of hydrogen and one atom of oxygen to form water the important thing I want you to focus on is those four electrons that I'm selecting over there if you notice those four electrons are not shared with hydrogen at all which means to say they are free to roam around the highlighted region the electron is not always in a fixed position they're just basically moving around and they are constantly moving on the bottom area this is what we call a surplus of electrons roaming the oxygen end of the atom now if we also look at hydrogen atoms the tops of the hydrogen atoms where I've highlighted have a lack of electrons roaming around the region this is now known as something called an unequal electron distribution unequal electron distribution just basically means that some areas of the atom has more electrons some areas of the atoms have less electrons so if you look at this molecule of water here the oxygen site has an extra surplus of electrons and the hydrogen side has a lack of electrons at the top the consequence of this is it makes oxygen now have a partially negative charge or the symbol of the symbol that I have just basically uh drawn that is just a Delta negative or you can also use partially negative and the hydrogen end due to its lack of electrons at the top will have a partially positive charge or the Delta positive charge it's not to be confused with ionic charges ionic charges are different this is just a very weak partially positive or weak partially negative charge the importance of uh it's kind of you don't have to know why it has a partially positive of a partially negative charge all you just have to know is water itself the hydrogen and it's partially positive and the oxygen and is partially negative and because of this water is also referred to as something called a dipole the word pole means charges and the word die in this case means two so water has two charges it's partially positive and it's also partially negative at the same time this is important because if we were to just basically draw out a water molecule a few water molecules over here notice that wherever there's a partially positive charge it will form hydrogen bonds with the partially negative side this and the hydrogen bonds I've signified over that in the dotted lines a very important point to also know is I've also highlighted the oxygen in the middle due to its size oxygen can actually form hydrogen bonds with two different hydrogen at the same time so if you look at the oxygen the highlighted oxygen atom there are two hydrogen bonds one going towards the lower left one going towards the lower right this is due to the size of the oxygen atom hydrogen atoms can't do that hydrogen atoms can only form one hydrogen bond due to its size so a lot of times students will assume that hydrogen can also form two hydrogen bonds it does not it's not able to form two hydrogen bonds that's a mistake over that other molecules may also form hydrogen bonds okay molecules with oh groups molecules with NH groups and also molecules with Co groups a molecule with an oh group the hydrogen and will have a partially positive charge NH group will have a the hydrogen has a partially positive charge as well but the C double bond o the oxygen atom has a partially negative charge this is important to know because when we cover amino acids and lipids later this is important right for example if I were to just basically take a molecule with an o h group and another molecule with a C or group you can see that the hydrogen and on the the hydrogen n which is partially positive can form a hydrogen bond with the oxygen and which is partially negative that's basically it