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Worked example: calculating ion charge

An atom with an electric charge is called an ion. The charge of an ion is equal to the number of protons minus the number of electrons. Created by Sal Khan.

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  • duskpin ultimate style avatar for user Tianyue Ma
    How and why would an atom lose electrons?
    (8 votes)
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    • sneak peak green style avatar for user 🍒Red🍒-😎😉👌🎶
      So basicly all atoms want is a full outer shell so they can gain stabitlity. They need to have a full outer shell of electrons so they can be stable. For example if a atom had a outer shell with 2 electrons it would rather lose those 2 electrons (causeing a chemical reaction) than gain 6. So it woudl lose these 2 electrons. And if your asking "hey that outer shell isnt full anymore its EMPTY" well, a shell with no electrons is basicly no shell so the shell before would become the outer shell. HOPE THIS HELPS (sorry for posting this answer in the comment earlier guys) ALSO RIP MY SPELLING
      (9 votes)
  • ohnoes default style avatar for user Panda1904
    why are there 2 blank spaces in the periodic table ?
    (4 votes)
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    • boggle green style avatar for user TDJ
      The 2 blank spaces mark the Lanthanides and Actinides, two series of elements that fit into those spaces. There are 14 elements in each of these groups. If they were included where the spaces are, the periodic table would be much wider (32 columns instead of 18 columns). Often, they are instead placed underneath the rest of the periodic table to compact it.

      I hope that this helps! =)
      (9 votes)
  • blobby green style avatar for user ipek1262
    when fnding the charge of an ion does the number of neutrons matter
    (4 votes)
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  • stelly green style avatar for user Anushka
    What causes an atom to become an ion?
    (1 vote)
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    • boggle green style avatar for user TDJ
      An atom has no charge, as it has the same number of protons (1+ charge) as electrons (1- charge). An ion has either more or less electrons than protons.
      Atoms become ions by gaining or losing electrons.

      I hope this helps! :-)
      (5 votes)
  • duskpin ultimate style avatar for user kunling802
    So what do you call an atom that is both an ion and an isotope? Like Sal's last example of 7 protons, 8 neutrons, and 10 electrons.
    (1 vote)
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    • leaf red style avatar for user Richard
      Isotopes are just atoms of the same element, same proton number, but different number of neutrons. So all atoms are themselves isotopes since there are other atoms of the same element with different numbers of neutrons. There is no single ‘standard’ nonisotope version of an element.

      Since it has a charge with excess of electrons, it would just be an ion.

      Hope that helps.
      (4 votes)
  • blobby green style avatar for user Tariq Zeyad
    the periodic table in the video has that strange effect, when you look at an empty space in between two elements, you can notice via your peripheral vision that there are some brown\orange dots in the other empty spaces in between elements, but once you look at the dots they disappear and appear on other places and again, you can only notice them with you peripheral vision, and the cycle goes on. sorry this is the best I could explain because I forgot the name of this phenomenon.
    (2 votes)
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  • aqualine sapling style avatar for user leahhong88
    If there are for example 20 protons and 18 electrons as shown in the video, could you write it as Ca^+2 or does it have to be Ca^2+? I used the ^ exponent symbol to just demonstrate the charge looking like an exponent if that makes sense.
    (1 vote)
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Video transcript

- [Instructor] So we're asked, what is the charge of a calcium ion with 18 electrons? So pause this video and see if you can work that on your own. And I will give you a little bit of a tip. A periodic table of elements might be useful to see where calcium sits on that periodic table of elements. So why don't you pause this video and see if you can figure out the charge of that calcium ion. All right, so what defines the element is actually how many protons it has, and that's what we have right over here. It's a atomic number is 20, that's how many protons it has. So we could say number of protons which provide positive charge is 20. And then we know the number of electrons is 18. That's negative charge. So I'll just write it here. Number electrons, I'll abbreviate it right over there or I'll shorten it. That is 18. And this has negative charge. So if you wanna know the net charge, you take the number of protons, the positive charge and subtract out the number of electrons. And so that leaves you with positive two charge, 20 minus 18 is positive two, and we will denote that with a two plus. So some people might write this as calcium 2+ just like that. To show that it is a calcium ion, it's likely a situation maybe where the calcium originally had 20 electrons and 20 protons. So then it would not be an ion, it would just be a neutral atom. But maybe it lost those, it lost two of those electrons and so then it got a positive two or a two plus charge. Let's do another example over here. So if I were to ask you what is the charge of an ion that has seven protons, eight neutrons, and 10 electrons, pause this video and think about what that would be. Well, we can confirm that that indeed would be an ion because it has a different number of protons than it does electrons. And if you wanna figure out the charge, you just take the number of protons, seven, which are the positive charges, and you subtract out the negative charges. That's why you're subtracting, you subtract out the electrons. So seven minus 10, that would be equal to negative three. And so I would say you'd often denote that as saying a three minus charge. And if you wanted to write down what ion that is, once it's gonna go back to the periodic table of elements, we can see that if you have seven protons, by definition you are talking about nitrogen. So that would be a nitrogen ion that you would denote like that. It has a negative three or a three minus charge.