But, what we're gonna do in this video is connect it to the masses Mass at an atomic level, or at a molecular level. Idea of average atomic mass, which we began to realizeĬould be a very useful way of thinking about a In a previous video, we introduced ourselves to the I hope this story/example helps out as a starting point for what can be a very difficult concept depending on how it is approached.

Then I would go into the more specific and accurate details given by Just Keith to explain the concept thoroughly. Now, for Chemistry when dealing with atoms, compounds or particles of elements, the 'convenient number' is the mole, which makes the use of the atomic mass numbers on the Periodic table manageable and much easier to use both in theoretical calculations and practical experimentation with chemicals. The last item, the salt, it would not be feasible to count out grains or even to determine the grain size being consistent, but would be more like the problems encountered for the much smaller atom/compound/molecule. I would just like to add maybe an even more basic explanation that I would employ to start with: when going to the grocery store to shop for you and your family, you would not pick up eggs individually anymore, or say 27 mL of milk or a specific amount of grains of salt (say 5000 grains), you would get say a donzen eggs, a litre/gallon of milk and specific mass/weight in gram/ounce of salt depending upon which unit of measure you use, this being more convenient and manageable number(s) when shopping. I agree completely with Just Keith's answer of the over complication of this video along with his great detail on the background and mathematics of the mole and atomic mass unit. I was just trying to show why 1 mole of amus equals 1g. Generally when working with Avogadro's number and the mass of a proton or neutron, you wouldn't substitute the values in. I suggest comparing line-by-line with the above example to see the similarities.Įxample 1: Let's determine the mass of 1 dozen eggs.Įxample 2: Show that 1 mole of 12C is 12g. I've included an example below showing the same concept to the above example but in a more familiar context.

I also think they chose to invent the mole because the mass of a proton or neutron is such a small number that they needed a way to descibe the mass in quantities that we can work with. I think that 1 mole was chosen to be 6.02x10^23 so that when it was multiplied by the amu it would give a nice number like 1g (shown above). (Please note: Some of the numbers above have been approximated and rounded but for simplicity I've left that stuff out.)

Molar mass is calculated by adding the relative atomic masses (Ar) of each atom of each element present in the formula.Ĭopper Sulfate: M (CuSO4) = 63.5 + 32 + 4 x 16 = 159.5 gmol-1Įxample: A sample of chlorine gas (Cl2) has 4.0 mol of substance.Ĭalculate the number of chlorine molecules.ġ molecule of chlorine (Cl2) contains 2 atoms of chlorine (Cl).Ĭalculate the amount of substance, moles, of 36 g of water, H20.Ĭalculate the mass of 5.Hi, this is the way I came to understand the concept of a mole.The molar mass (M) of an element is defined as the mass of 1 mol of the element expressed in grams per mole (gmol-1).The number of atoms or ions in 1 mole of an element or compound is 6.02 x 10^23 and is called Avogadro’s number (N A).A mole is defined as the amount of substance that contains as many elementary particles (atoms, molecules or ions) as there are atoms in 12 g of carbon-12 isotope.The word mole (symbol, mol) represents a number.To calculate the number of carbon-12 atoms that are present in 12g of carbon-12 we need to know the mass of 1 carbon-12 atom. Carbon-12 isotope has a relative mass of 12.

Moles to particles