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What is the cause of an atom's number of protons

  1. Dec 21, 2014 #1
    Why is it that one atom such as hydrogen has one proton while others have many. What is the mechanism driving this force which causes some atoms to be marked for one protons and others for many? And once they are say marked as hydrogen they can be nothing else, correct? Since hydrogen is the simplest of all atoms than would this make hydrogen the most abundant element in all the Universe? And lastly is there a limit to how many protons/electrons/neutrons an atom can possess?

  2. jcsd
  3. Dec 21, 2014 #2


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    To answer your questions there are many steps.
    1. Big bang leads to a universe with most of the baryonic matter is hydrogen, while most of the rest is helium.
    2. Gravity leads to matter clumping together to form stars. Inside stars nuclear fusion takes place creating elements up to iron.
    3. When these early stars run out of hydrogen and other light elements to fuse, some explode leading to creation of heavier elements.
    4. Elements heavier than lead (more than 82 protons) are radioactive and decay into lighter elements. Uranium lasts a long time. When you look at elements that are heavier, they don't last very long.

    I suggest you look up (Wikipedia) articles about big bang, nuclear fusion, radioactivity, star formation, star lifetimes.
  4. Dec 21, 2014 #3


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    Any atom that has one proton (and zero, one, or two neutrons) in its nucleus is by definition hydrogen. However, under the right circumstances hydrogen nuclei can be forced together to form helium nuclei, so it's not right to say that once it's hydrogen it can't be anything else. It would be more accurate to say that as long as it has one proton it's hydrogen and as soon as that changes it becomes something else.

    For an atom to be stable, the number of electrons must equal the number of protons - otherwise it won't be electrically neutral and electrostic forces will either attract or repel electrons until the count balances.

    Neutrons and protons are less simple; a nucleus will be stable if it has the right mix of neutrons and protons, but the rules are fairly complicated. For example hydrogen-1 (one proton, no neutrons) and hydrogen-2 (one proton, one neutron) are stable, but hydrogen-3 (one proton, two neutrons) decays into helium-3 (two protons, one neutron). At the other end of the range, uranium-238 (92 protons, 146 neutrons) is fairly stable but uranium-236 (same 92 protons but only 144 neutrons) is ridiculously unstable and splits into two lighter elements almost the moment it is created. beyond 92 protons, just about no nucleus is stable.
  5. Dec 21, 2014 #4
    @Nugatory Why is Uranium-238 stable but not Uranium-236, why does subtracting two neutrons cause such dramatic effects? If I understand it correctly neutrons are basically bi, right?

    @mathman If I am following correctly. An element with many protons is essentially either a hydrogen or helium atom because those the simplest of all elements. Therefore, all other elements are derivatives of those two elements? And the only way complex elements are created is through the things like nuclear fusion (things of this nature) taking place. So gold is just hydrogen+helium which underwent a unique set of events? same with the other elements?

    And Thank You for your input! I am learning a lot here.
  6. Dec 21, 2014 #5


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    Neutrons are neutrally charged, so they don't repel each other or the protons. However, neutrons attract protons and other neutrons by the short range "strong nuclear force". The simplified answer is that subtracting two neutrons decreases the attraction but leaves the repulsion alone, resulting in a nucleus that is much more unstable than before. You would have to learn about various quantum effects to understand all the details about why this results in an unstable nucleus.

    It is true that hydrogen is the simplest element, consisting of one proton, but I wouldn't say that all elements are "composed of hydrogen". Hydrogen, as an atom/element, is a very specific thing. Helium, the next element up the chain, is composed of two protons but I wouldn't say that it's composed of hydrogen, but of protons. In other words, "Hydrogen" specifically means the element or atom, including its chemical properties. "Proton" refers to a specific subatomic particle that makes up all elements, of which hydrogen just happens to have one. There's also the fact that elements, including hydrogen, have different isotopes, so saying something is made of hydrogen and/or helium doesn't really help since you'd also have to specify which isotope, of which there are many.

    The short version: Atoms/elements are composite particles made up of smaller subatomic particles. Heavier atoms aren't composed of lighter elements, but are different elements in and of themselves.
  7. Dec 21, 2014 #6
    To get this all in order:
    Protons repel protons
    Neutrons attract protons and other neutrons due to the strong nuclear force
    Electrons attract protons but repel other electrons
    Is this correct?
    And what effect/relationship do the electrons have on neutrons?

    Is this unstableness true for subtracting neutrons from all elements as well? Neutrons are what "bonds" the protons to the atom correct? The less of them, the less bonding they have and thus the more unstable the atom?

    I understand that all elements have their uniqueness and are specific, but wouldn't they have to start out as a hydrogen or helium atom first to then result in something more complex? I shouldn't have referred to them as being combined or something as if that could happen over night. But as a result of something that took millions or billions of years to form. Wouldn't they have to get their protons from hydrogen or helium? As I imagine after the big bang those would be the first things to come about, if in fact all protons are made the same? That is there is no proton that is any different than the other?

    Also, a little off topic but it sort of relates to this and getting a better understanding. There was nothing, then the Big Bang everythingness shoots in all directions. Was this everythiness (as I call it) composed of just protons? and the expanse and the "forces" as they came about manipulated them to form atoms? Was there ever a time without atoms or protons? In the beginning what was this everythiness made of during the start of the Big Bang?

    Thank You!
  8. Dec 22, 2014 #7


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    Mostly. Protons also attract each other via the strong nuclear force. They just also happen to repel each other via the electromagnetic force.


    In general, yes.

    Sure, for millions to billions of years most of the matter exists as ether hydrogen or helium prior to collapsing into a star and undergoing nuclear fusion. Still, since an atom is a composite object, I wouldn't say that any elements are made out of other elements.

    Well, ignoring the part about nothingness turning into something and a big explosion, which isn't really correct but we won't get into here, the very early universe consisted of a very hot, very dense plasma of quarks, various bosons, and high-energy radiation. As the universe expanded, this plasma cooled off and became less dense, eventually reaching a point where the temperature was low enough for nucleons to form, protons and neutrons. The temperature continued to fall until it reached a point where nuclear fusion could take place. This lasted something like a few minutes and then the temperature was too low and fusion ceased, leaving the universe as about 75% hydrogen and 25% helium by mass, with electrons as a tiny fraction of a percent. Then, after this, the temperature continued to fall until it reached the point where electrons could combine with protons and form the first atoms, an event called recombination.
  9. Dec 23, 2014 #8
    I know this is a broad question but why does it fall into any order at all? Meaning, what is the reason (if any) that these forces exist to allow them to become in the first place. I am very curious about the nature of 'forces' and why they "eloquently" exist. Why are forces set in a such a specific ways as to allow for the creation of such things as protons, neutrons and electrons. Seems that things could have gone an infinite number of ways but things happen to follow this specific and neat path allowing for the development of such complex things, why is there this allowance of such things as 'forces' how do these forces come into existence? And is there any (idk if this is the correct word to use) energy behind forces? do they ever run out of "juice" so to speak of there force?

    Other questions I have are:

    How exactly does this work? if one is repelling and the other is attracting, is one countering the other is an infinite tug of war keeping each other in check by balancing each other out?

    I couldn't find a definition on "composite object" is this to say that the atom is composed of many things which are completely independent of classification of an elements. Therefore, an atom is by itself its own unique "object". And hydrogen/helium are just using atoms as a sort of cosmic taxi for their character/qualities.

    When you state that it lasted something like a few minutes, just to clarify. Do you actually mean a few minutes by a carl sagan way of speaking or in everyday time keeping?

    And Thank you!!!! This is interesting stuff
  10. Dec 23, 2014 #9


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    Perhaps things could have gone any number of different ways, but that is beside the point. We can only study the way in which our universe ultimately formed. That is a complex enough undertaking in and of itself.

    In order for atoms more complex than hydrogen to form, some mechanism must allow the atomic nucleus to contain more than one proton. Having different forces counteract one another is not something exotic.

    The term 'composite object' means that an object is composed of several distinct components or parts. An object like a car or an airplane is an example of a 'composite object', one which is formed by assembling many different kinds of smaller objects into a single whole.

    It's not clear what the rest of your writing means. One atom of hydrogen is indistinguishable from another; one atom of calcium is indistinguishable from another, etc., etc.

    IDK what a 'cosmic taxi' is.

    It was a relatively brief period. These time scales are only estimates; there was no one using a stop watch to measure the exact interval.
  11. Dec 23, 2014 #10


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    That is indeed a good question, but unfortunately there is no answer to it. It's just the way things are. Why are forces they way they are? Why do they even exist in the first place? These aren't questions we can answer.

    They do not. In fact it is energy that is dependent on forces, not the other way around. That is to say that energy is the result of a system of objects and the forces they interact with being in a particular configuration. We can't change how the forces act, but we can change the energy simply by moving objects around. For example, we can't change how gravity works, but I can lift up a rock and drop it, which changes the energy of the rock.

    The strong force is MUCH stronger than the EM force, so the attraction is stronger than the repulsion. To a point. The issue is that the strong force is VERY short ranged. It only works over the distance of about 2 or 3 nuclei. The repulsive EM force, on the other hand, has an infinite range, with the strength falling off much more slowly. So when you pack the nucleus full of several hundred protons and neutrons, like in a uranium atom, all of the protons repel each other via the EM force. However each proton only feels an attraction from a few other nuclei. Throw in some quantum effects that we won't get into here, and bam! Unstable nucleus that's ready to pop.

    Yes, the fundamental particles that compose an atom are independent in and of themselves. It's kind of like a chorus. Each singer is unique, with their own looks, sound, etc. But when they join together and sing as one, you get a different sound altogether, which changes based on how many singers there are, how many are in each vocal range, etc.

    I thought I remember reading it was literally a few minutes, but I can't find the reference.
  12. Dec 23, 2014 #11
    Strong Force=very strong but short range
    EM Force=Infinite range, but not that strong

    It's only when protons are within very tight spaces that they attract each other, and outside of 2-3 nuclei they start becoming unstable because of the EM force?

    Could an atom be though of as say an big instrument case? like it can hold any number of one "instruments" (Elements) and each one gives the case a different function. Like the atom being the casing or something that facilities a use?

    Thanks for the replies Drakkith you are such a help and a wealth of information!
  13. Dec 23, 2014 #12


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    Pretty much. It's obviously much more complicated than how I'm putting it, as we haven't even talked about quantum effects, but that's the gist of it.

    Not really. I'd say an atom is more like the instruments themselves. Just think of all the tools you can make out of two or three materials. A thousand different wrenches, ratchets, gauges, etc. Each one is different because of the way it's been put together, despite the fact that they may all be made up of the same materials.
  14. Dec 23, 2014 #13


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    You mean nucleons, not nuclei (which is the plural of nucleus).
  15. Dec 23, 2014 #14


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    Without the presence of neutrons, the protons will not stick together. Even Helium has two neutrons - and it has an extremely stable nucleus, surviving a lot of knocking about in many nuclear reactions (Alpha particle).
    There is very little point trying to come up with your own set of rules for this because it is very complicated and it all hangs on much more detailed knowledge than yours (or mine!). After all - it took a lot of very bright Physicists to arrive at the rules, even with all the information that was available. You ask, for instance, about stability of the different isotopes; that's a very hard question and has no arm waving answer.
    I strongly suggest you try reading a few Popular Science books (of which there are many available) or even a text book or two. http://www.met.reading.ac.uk/pplato2/h-flap/phys9_1.html [Broken] may be worth looking at. It has a lot of useful information in it but not a lot of explanation as it is a Module description.
    Last edited by a moderator: May 7, 2017
  16. Dec 23, 2014 #15
    Which brings me to another question do we know how do protons, electrons and neutrons come about in the firs place.
  17. Dec 24, 2014 #16


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    Whoops, you are correct.
  18. Dec 24, 2014 #17


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    Yes, we know how they can be created. Is that what you're asking?
  19. Dec 24, 2014 #18
    Indeed! I'd like to know
  20. Dec 25, 2014 #19


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    The general idea. The big bang led to a lot of energy (photons) in a very small volume. Photon-photon collisions resulted in quark-antiquark pairs as well as electron-positron pairs. For some reason (still unknown) an excess of matter particles (quarks and electrons) survived. As things cooled down, quarks combined (in triplets) to form protons and neutrons.
  21. Dec 25, 2014 #20
    What caused these quarks to combine, and why in triples?
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