 # Isotopes and Elements Practice Problems here in this video we're going to look at how to figure out and solve for all of these characteristics or properties of an atom if you want to follow along yourself you'll need a periodic table so that you can look up atoms as we go so given just these two pieces of information we've got to figure out everything else this is kind of like a puzzle or a logic game kind of like pseudo ku we'll go step by step so you can see how to do this let's start here the chemical symbol is na so we'll look up na on the periodic table and we'll find out that that is a symbol for sodium so now for the isotope name we know that this is going to be sodium now that's only the first part the isotope name tells us what element it is and then it has a mass number after number of protons plus the number of neutrons the mass number has already been given to us so we know the isotope name is going to be sodium from na and then 22 from the mass number now that we know that na is sodium we can fill in the atomic number and the number of protons because when we look this up on the periodic table and a sodium has 11 at the top this number up here is the atomic number number protons so 11 for the atomic number 11 for the number of protons now for the number of neutrons the mass number here is the number of protons plus the number of neutrons so if we want to find out just a number of neutrons we can do protons and neutrons - protons equals 11 neutrons that's how many... neutrons we have now finally for electrons let's look it up at our Sigma let's look up here at our at our symbol okay it's written na 1 plus because there's just one plus sign there so it's 1 plus okay this is the net charge the net charge tells us how protons and electrons balance out so if it's 1 plus that means there is one more proton than electron so 11 protons which means that we have 10 electrons we'll give this atom a 1 plus charge so based on just these two pieces of information we are able to figure everything else out here we know protons neutrons and electrons let's start with protons 44 here we can look up on the periodic table and find out which element has an atomic number of 44 okay you got 44 your ruthenium so I can put that up here is the isotope name ruthenium but I'm still going to have to come back and deal with a mass number that we put after here in the isotope name atomic number I can take care of that right away it's 44 the number of protons don't even have to look it up on the periodic table to fill this in let's move ahead now to a to mass number mass number is protons plus neutrons so I'll do 44 Plus 56 that's going to give me a hundred total for the mass number now I know the mass number so I can put it here at the end of the isotope name ruthenium 100 and I'm all set with this the only thing that I have left now is the chemical symbol with a net charge let's go back to the periodic... table here it is to find out what the chemical symbol is a chemical symbol is right here is ru and now for the net charge that we'll put up here two protons and electrons so there are 44 protons and 40 electrons that means there are four more protons than electrons so there's going to be a net charge of 4 + ru 4 plus is going to finish this off as the chemical symbol with a net charge iodine-131 and it has a negative charge 1 - let's start by looking it up on the periodic table we find iodine big capital letter I it has an atomic number of 53 so 53 here 53 is also the number of pro the number here that comes in the second part of the isotope name is the mass number the number of protons and neutrons together so based on this information mass number I can find number of neutrons so protons plus neutrons - protons - 53 it's going to give me 78 that's the number of neutrons and finally the electrons up here on the chemical symbol we get the net charge it has a 1 - charge there's 1 - there so that means that we have to have one more electron than protons so 43 protons I'm sorry 53 protons I can count I can count 53 protons 54 electrons and finally mg 2 plus with 13 neutrons I'll look this up on the periodic table if you didn't already know this mg is magnesium so I'll write that in here magnesium you look up magnesium on the periodic table you can get the atomic number right up here so that's 12 the number of protons is also 12 because... they're the same thing and now that I know protons and neutrons I can get the mass number 12 protons plus 13 neutrons equals 25 there's my mass number and now I can use the mass number to finish up the isotope name up here it's going to be magnesium 25 finally I need to fill in my electrons from this symbol up here I can tell that I have a two plus charge on this ion two plus means that there are two more protons than electrons so if there are 12 protons I'm going to end up with 10 electrons so that's how you can solve

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like this you kind of got to go step by step figure out what you can do from each step and then you'll just see the information kind of clicks together you know just like you're doing a puzzle or Sudoku or something like that