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Worked example: Identifying isotopes and ions

Identifying isotopes and ions from the number of electrons, protons and neutrons, and vice versa. 

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  • duskpin tree style avatar for user deeps
    what is the difference between the element hydrogen and the isotope of hydrogen?
    (17 votes)
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  • aqualine ultimate style avatar for user madeinthe1980s24
    Great video! I do have a question though. Where do elements actually pick up extra neutrons? I am assuming the non-synthetics exist in nature as what they are on the periodic table. Am I correct in assuming as such?
    (19 votes)
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    • spunky sam blue style avatar for user Ernest Zinck
      We are all made of stardust.
      Almost every element on Earth was formed at the heart of a star.
      It started after the Big Bang, when hydrogen and helium gathered together to form stars.
      At the stars’ cores, hydrogen and helium nuclei fused to beryllium and carbon.
      As these heavier nuclei were produced, they too combined inside stars to form all sorts of nuclei with different numbers of neutrons.
      During supernovae, the different elements disperse across the universe, and these now make up the planets including Earth.
      (19 votes)
  • aqualine ultimate style avatar for user janet
    what is ion? what is the relationship between isotopes and ions?
    (8 votes)
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  • aqualine tree style avatar for user 20lovins.adalynne
    What is the difference between an isotope and an ion?
    (6 votes)
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    • leaf blue style avatar for user Nishanth
      Isotopes are those atoms having same atomic number (number of protons are same) but different mass number (number of neutrons differ).

      Ions are atoms which contain an overall charge (where number of protons ≠ number of electrons )
      (10 votes)
  • duskpin tree style avatar for user mariam tagourti
    so does that mean that you can figure out the number of protons by looking at the top of the element?
    (3 votes)
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    • piceratops seed style avatar for user RogerP
      He means that if you look at the periodic table, then each element is in a box and the uppermost number in the box is usually the atomic number, which is the number of protons. (In the table in the video, the top number in the hydrogen box is 1, for helium it is 2, lithium 3, etc.)

      There are lots of different ways of presenting the periodic table, so you will find exceptions to this. However, the atomic number is always shown somewhere and it is always an integer that increases by 1 as you move from element to element across the table, from left to right.
      (7 votes)
  • female robot grace style avatar for user Dhruv Rajput
    i know this is a stupid question but i m confuse .. how can we so sure that an element has same no. of protons as mentioned in periodic table? as we know that atoms are very small and protons are even smaller then how no. of proton is counted?? Actually i want to ask how do we count no. of protons ??
    (5 votes)
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  • starky ultimate style avatar for user Ved Pant
    What's the difference between an Isotope and an Ion?
    (1 vote)
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    • piceratops seed style avatar for user RogerP
      Isotopes are atoms that have the same numbers of protons but different numbers of neutrons.

      An ion is an atom that has gained or lost electrons, so it now has more or fewer electrons than it does protons. So an ion has a negative or positive charge.

      All atoms are isotopes and if an isotope gains or loses electrons it becomes an ion.
      (7 votes)
  • blobby green style avatar for user jessicalacorte6
    And here is where I got confused. My chemistry teacher said the atomic # of an element is equal to the # of proton likewise the electron. Example Carbon's atomic #is 6 and atomic mass of 12 so, the no. Of proton=6 electron= 6. But here, it's just different. And that's why also I can't answer your practices correctly. Why?how? Somebody
    (2 votes)
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    • boggle blue style avatar for user Davin V Jones
      It isn't different. For protons, the number always equals the atomic number of the element.

      Ions are atoms don't have the same number of electrons as protons. If you are told an atom has a +1 charge, that means there is one less electron than protons. If it has a -2 charge, there must be two more electrons than protons. Carbon with a -2 charge must have 8 electrons (6 protons/electrons in neutral atom plus 2 more electrons to give it a -2 charge = 8)

      Isotopes are simply specifying the number of neutrons and protons (together called nucleons) in the atom. So, Carbon-12, which has an atomic mass number of 12, has 6 neutrons (12 nucleons - 6 protons = 6 neutrons). Carbon-13, which has an atomic mass number of 13, has 7 neutrons (13 nucleons - 6 protons = 7 neutrons).
      (6 votes)
  • primosaur sapling style avatar for user AmirParsa
    Can an atom have less neutrons than its Protons?(except hydrogen)
    (3 votes)
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  • starky tree style avatar for user Reem
    Why does an element tend to have isotopes? I mean why and how would a neutron get added and how will it affect the atom if the element will remain the same?
    (1 vote)
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    • boggle blue style avatar for user Davin V Jones
      Atoms can vary in the number of particles they have. They can have different numbers of protons, neutrons and electrons.
      When we refer to an element, we are specifying a specific number of protons.
      When we refer to an ion, we are specifying a certain number of electrons not equal to the protons.
      When we refer to an isotope, we are referring to the total number of nucleons for an element, which an element has a specific number of protons so the neutrons can vary.
      We can take it another direction and refer to isobars, which have the same number of nucleons, yet can vary in protons and neutrons.
      We can also refer to isotones which have the same number of neutrons yet different protons counts.

      Back to neutrons and isotopes, the neutrons can vary by the production of the atom, by fusing different combinations to give varying neutron counts. Also neutron capture, where a free neutron directly interacts and fuses to a nucleus can change the neutron count. Finally, radioactive decay from various other atoms can produce various different isotopes of an element.
      (5 votes)

Video transcript

- [Narrator] An isotope contains 16 protons, 18 electrons, and 16 neutrons. What is the identity of the isotope? And I encourage you to pause the video and see if you can figure it out and I'll give you a hint, you might want to use this periodic table here. All right, so I'm assuming you've had a go at it. So, an element is defined by the number of protons it has. So if someone tells you the number of protons, you should be able to look at a periodic table and figure out what element they are talking about. So, because it is 16 protons, well we can go right over here to the atomic number, what has 16 protons, well anything that has 16 protons by definition is going to be sulfur right over here. So I could write a big S. Now, the next thing we might want to think about is the mass number of this particular isotope. Remember, an isotope, all sulfur atoms are going to have 16 protons, but they might have different numbers of neutrons. So, the sulfurs that have different number of neutrons, those would be different isotopes. So, this case we have 16 protons and we have 16 neutrons, so if you add the protons plus the neutrons together, you're going to get your mass number. So 16 plus 16 is 32. Now let's figure out if there's going to be any charge here. Well, the protons have a positive charge. The electrons have a negative charge. If you have an equal amount of protons and electrons, then you would have no charge. But in this case, we have a surplus of electrons. We have two more electrons than protons and since we have a surplus of the negative charged particles we, and we have two more, we're going to have a negative two charge and we write that as two minus. So this is actually an ion, it has a charge. So this is the isotope of sulfur that has a mass number of 32, the protons plus the neutrons are 32, and it has two more electrons than protons which gives it this negative charge. Let's do another example where we go the other way. Where we are told, we are given some information about what isotope and really what ion we're dealing with because this has a negative charge and we need to figure out the protons, electrons, and neutrons. Well, the first thing that I would say is, well look, they tell us that this is fluorine. As soon as you know what element we're dealing with, you know what it's atomic number is when you look at the periodic table and you can figure out the number of protons. Remember, your atomic number is the number of protons and that's what defines the element. That's what makes this one fluorine. So let's go up to the, our periodic table and we see fluorine right over here has an atomic number of nine. That means any fluorine has nine protons. So, let's scroll back down. So, must because it is fluorine, we know we have nine protons. Now what else can we figure out? Well, we know we have a negative charge right here and this is, you can use as a negative one charge and so we have one more electron than we have protons. And so since we have nine protons, we're going to have 10 electrons. And then finally how many neutrons? Well, remember, the neutrons plus the protons add up to give us this mass number. So, if you have nine protons, well how many neutrons do you have to add to that to get to 18, well you're going to have to have nine neutrons. Nine plus nine is 18.