[Music] more everything in and around us is made up of atoms atoms combined to form molecules for example hydrogen atoms combined with oxygen to form water molecule h2o atoms and molecules are extremely small how small tip of a pen contains one trillion hydrogen atoms diameter of a water molecule is 0.3 nanometer that is 10 to the power minus 9 meter because of extremely small size of atoms it is very difficult to count them and in order to observe manage and deal with these small atoms and molecules chemists came up with the term mole mole not the animal nor the spy neither the one on your uncle's face in chemistry mole is just a number as we buy socks in pairs X in dozen paper in a rail similarly in chemistry deal with atoms in mole as a pair means to a dozen means 12 re means 501 mole is essentially six zero two to one four one seven nine zero zero zero zero zero zero zero zero zero zero zero zero zero zero zero of something to make life easier write it as six point zero point two x 10 raised to the power 23 so if someone asks you for two moles of water you no they are asking for 2 x 6.02 x 10 raised to the power 23 water molecules experiments are so much fun let's say some moles in action by doing a simple experiment with gems and ladoos yummy take a big beaker and put as many marbles in that container as possible now try to put some number of ladoos in that container is this possible however gas molecules do not behave like humans if you take hydrogen and oxygen in same volume vessels you can put the same number of molecules in 1811 and Italian scientist Amedeo Avogadro observed this behavior of gases and proposed that the volume of a gas at a given pressure and temperature is proportional to the number of atoms or molecules regardless of the nature of the gas when Avogadro first proposed this hypothesis it was hard for people to accept it many years later other scientists experimentally determined that a Bouguereau was right and a fixed volume of gas contains six point zero 2 multiplied by 10 raised to the power 23 atoms and it was called a moon since Avogadro was the first one to observe this a mole is also known as Avogadro's constant since now you know what a mole is can you tell me the number of moles in 360 grams of water to answer this correctly you need to know mass of one mole of water in grams we use the periodic table to find out the mass patterns for example oxygen its atomic number is 8 which is written at the top of the symbol and the number written at the bottom represents its atomic mass molecule mass is determined by adding atomic mass of individual atoms present in a molecule experimentally chemists have determined that mass of one mole of an atom or molecule is equal to its atomic or molecular mass in grams 18 gram of water 55 gram of fine 32 gram of oxygen 58.5 gram of salt 197 gram of gold and for gram of helium each contain one mole of atoms or molecules using this logic we can find number of moles of any substance by adding given mass of the substance with its molecular mass so number of moles in 360 grams is equal to 360 divided by 18 gram of water second way of finding moles is by knowing the exact number of particles for example if you have three point zero one multiplied by 10 raised to the power 23 oxygen molecules you can find the number of moles by dividing it with Avogadro's constant so in this case we have 0.5 moles of oxygen we also have a third way of finding modes for gases if you are given volume of any gas in liters at standard temperature and pressure then it's number of moles can be determined using the formula given volume upon 22.4 I hope moles will not bother you any more please like share and comment on the video and don't forget to subscribe to our YouTube channel for more interesting and educational videos to earn while you learn download extra class app from Google Play Store and get rewarded for star