[Music] hi and welcome back to free science lessons by the end of this video you should be able to interpret a chemical formula now sometimes students find this tricky initially but they soon get the idea so stick with it we've already seen that the periodic table shows us all of the different elements remember that each element has a symbol and every symbol starts with a capital letter some symbols then have a second lowercase letter this shows the chemical formula for the compound hydrogen fluoride a chemical formula tells us the elements in a molecule and the numbers of atoms of each element looking at the formula we can see the symbol for the element hydrogen and the symbol for the element fluene we can also use this formula to work out the number of atoms of hydrogen and fluid you can see that we have no number to the right of the hydrogen so that means that we have one atom of hydrogen we also have no number to the right of the fluene so again that means that we have one atom fluid this shows the chemical formula for the compound potassium iodide I'd like you to work out the elements in this compound and the number of atoms of each element so pause the video now and try this yourself okay we can see that this compound contains the element Potassium and the element iodine and again there are no small numbers to the right of these symbols so this compound has one atom of potassium and one atom of iodine this shows the chemical formula for the compound calcium sulfate we have the symbols for the elements calcium sulfur and oxygen again we can use the formula to work out the number of atoms of each element we have no small number to the right of the calcium this means that we have one atom of calcium in this compound there is no small number to the right of the sulfur so that means that we have one atom of sulfur and we have a small number four to the right of the oxygen so that means that we have four oxygen atoms in this compound now a key idea you need to understand is that in a specific compound the number of atoms of each element is fixed we can't change those numbers because if we do then we have a different compound on the left we've got the compound calcium sulfate and on the right we have the compound calcium sulfite so change in one small number means that we've now got a totally different compound okay here's another chemical formula this is the compound magnesium hydroxide you'll notice that this formula contains brackets so let's see what those mean well just like before we start by identifying the elements in the compound looking at the symbols we can see that we have three elements these are magnesium oxygen and hydrogen but what about the number of atoms well there's no small number to the right of the Magnesium so we have one atom of magnesium in this compound inside the brackets we've got oxygen and hydrogen and there's a small two to the right of the brackets a little number to the right of bracket multiplies everything inside the brackets so in this case we've got two atoms of oxygen and two atoms of hydrogen don't worry about why some compounds are brackets in their formula it's used by chemists to work out how the atoms bond together here are some more compounds for you to try I'd like to identify the elements in these compounds and work out the number of atoms so pause the video now and try this yourself okay in the first compound we have one atom of copper and one atom of iodine in the second compound we have one atom of iron and two atoms of bromine the third compound has one atom of zinc one atom of carbon and three atoms of oxygen and the final compound has one atom of aluminum three atoms of oxygen and three atoms of hydrogen you'll find plenty of questions on this topic in myvision workbook which you can get by clicking on the link above [Music]