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Video transcript

so my apologies I just had a deviated septum surgery yesterday but what we're going to talk about in this video is the notion of an ion so before we talk about ions we're just going to talk about the idea of an element for example if I have carbon carbon is an element and let's say I have one atom of carbon what do we know about that one atom of carbon well by definition an atom of carbon has six protons so it's going to have six protons and if it is neutral carbon it is going to have the same number of electrons it is going to have six electrons and that's what makes it neutral you have the six positive charges and the six negative charges now you could have a carbon ion although they aren't that typical the way you get an ion is if you don't have an equal amount of protons and electrons so for example if you had six protons and five electrons what would that be well we still have six protons and remember protons are what define what element we're dealing with so we're still dealing with carbon but now we have one more positive charge that we have a negative charge so this will be carbon with you could write it as a one plus charge like that or you could even write it like this and this you would just view as a carbon atom this you would now call an ion because it has that net charge it has a different number of protons and electrons what if you were to go the other way around what if you were to have five protons five protons and six electrons what would this be I'll remember protons define what element you're dealing with so now if you look at what element has five protons we're dealing with boron so this is going to be boron neutral boron will have five protons and five electrons but this one has one extra electron so it has one extra negative charge so you can write it like this one - or you could just say it has a negative charge so this is a boron ion right over here as soon as you have an imbalance between protons and electrons you no longer would call it an atom you would call it an actual ion now let's do an example question dealing with this so our question tells us our question our question tells us an atom and an atom of platinum has a mass number of 195 so let's just look up platinum on our periodic table platinum is sitting right over here if you could see it so an atom of platinum has a mass number of 195 and 195 looks pretty close to that atomic mass we have listed there and it contains 74 electrons 74 electrons how many protons and neutrons does it contain and what is its charge all right so let's think about this a little bit so we're dealing with platinum so by definition platinum has 78 protons so we know that it has 78 78 protons they cut they're telling us it has 74 electrons 74 electrons we like electrons so just from that we see we have four more protons than electrons so you have you would have a positive four charge four more of the positive things that you have on the elect of the negative things so you could write this as platinum with a plus four charge this is a platinum I on a positive platinum ion the general term when we're talking about a positive ion we're talking about a cation that is a positive positive ion up there when we talked about boron being negative a negative ion that is an anion this is just to get ourselves useful useful used to some of the terminology but we're not done answering the question they say an atom of platinum has a mass number of 195 and it contains 74 electrons how many protons and neutrons doesn't contain as what is its charge we figured out its charge we know the protons by definition platinum has 78 protons but what about its neutrons well protons plus neutrons it's going to be equal to our mass number it's going to be equal to 195 so we have 78 protons plus I'll say n 4 neutrons is equal to 195 subtract 78 from both sides and what you get the number of neutrons is equal to 1/100 let's see if I subtract 70 I'll get 100 n I'll get 125 minus 8 I have a hundred and seventeen neutrons so 117 neutrons and we're done but the big idea is and we say atom when we have the same number of electrons and protons that's when we are neutral but as soon as we become non neutral we have either more electrons or more protons and this is true of an atom or molecule we will then call it an ion and if you want to be a little bit more specific a positive ion is called a cation and a negative ion is called an anion