How do we know atoms have X amount or electrons and protons?

Factual Questions
1

How do we know for sure that a helium atom has only one electron and one proton?

Now, I understand that eletrons and protons will be the same in number otherwise they would have a positive or negative charge. (i.e. an ion)

What I’m trying to surmise is: Aren’t these numbers more or less a scale as opposed to an actual number? Or couldn’t you say that the helium atom is given it’s number in proportion to the oxygen atom? (and so forth)

if I’m not making sense, the jist of my question is: Is it implausible to think that there could be (theoreticaly) an element between a helium atom and an oxygen atom? Which I guess would mean such an element (Given our current elemental charts) would have 1 1/2 protons and 1 1/2 electrons?

Or if I’m still not clear:

How possible is it that there are elements out there (that aren’t radio active) that we haven’t discovered yet.

I mean space is a pretty big place, what makes us think we have every element here at our disposal on our small little planet?

2

Millikan’s Oil Drop Experiment

3

This is too long and complex a discovery trail to go through here. You haven’t given any hint as to your level of understanding of physics and chemistry so it would be necessary to start the explanation at the very beginning. You might go to the library and check out Vol. 3 of Isaac Asimov’s Understanding Physics. It contains a good description of the experimental process by which the structure of the atom was determined. There are probably lots of other accounts around of the building up of the atomic theory and the knowledge of the structure of atoms.

And no, there aren’t any undiscovered, non-radioactive elements in this universe having the physical properties that it has. The periodic table of the elements doesn’t have any room for them. And I think that any newly discovered, unstable elements beyond the current, heavy element end of the periodic table will have exceedingly shor half lives.

4

Nitpick: You have described here a hydrogen atom. A helium atom has two protons, two neutrons, and two electrons.

5

:smack: I knew I should have consulted the table before I submited this question.

I haven’t had a physics class in nearly 20 years.

I guess I’ve been watching too much sci-fi shows lately. All I really wanted to know is if it’s plausable that there could be more elements out there than we are aware of. All the afore mentioned stuff in my op was me more or less trying to surmise how that might be possible.

6

Well, that’s what hydrogen is. We’ve defined “hydrogen” to mean “a substance made of atoms containing exactly one proton” I don’t know if this really answers your question though.

7

The ‘could there be an undiscovered element between element Z and element Z+1’ question is one of a list of scientific questions in Carl Sagan’s The Demon-Haunted World. (The questions are meant to be thought-provoking, though some have clear answers, as this one does.) BTW, you meant helium and lithium, if you meant ‘between helium and the next element’, and hydrogen and helium, if you meant the proposed element that has 1.5 protons. There are several well-known elements between helium and oxygen. =)

The reasons why there can’t be elements with half-protons are a bit more complex than merely the fact that the charges of electrons and protons are quantized. It also has to do with the types of particles that can be present in atoms. For example, a proton is comprised of three quarks (two up quarks with a charge of +2/3, and one down quark with a charge of -1/3, for a total charge of +1). There can’t be half-charges, and I think a particle made up of, say, two up quarks is impossible. At any rate, partial protons and partial neutrons are not possible, and that’s the only way there could be undiscovered elements between the known elements. The only recourse is a fundamentally different kind of matter.

The ‘scale versus an actual number’ issue is an important one in the history of science, because in the past the atomic weights for several elements were wrong. For example, it was once thought that oxygen had an atomic weight of 32 and hydrogen of 2. This has more to do with a belief that diatomic gases were impossible than with measurement errors, but the correct atomic weights were finally figured out in the mid-1800s. We now know for several reasons – among them the oil drop experiment and quantum-mechanical calculations – that the atomic masses are actual numbers and not a scale. That is, hydrogen contains one proton and one electron and not n of each. This means that an element whose atomic number is Z has Z protons and not nZ, where n is the number of protons that hydrogen contains.

8

Well, there is a theory that there is an “island of stability” for nuclei with approximately 114 protons and 184 neutrons. These elements would theoretically have much longer half-lives (but still in the range of micro- and milliseconds) than the other “superheavy” elements. There are some interesting articles here and here.

9

Not very. We know what elements are out there, to the limits of the observable universe, by color of the light they emit; astronomical spectroscopy. The elements we know account for the emission spectra of even distant galaxies. In the early days of spectroscopy, there were new elements discovered in space. Helium was first detected in the spectrum of the sun, and only later found on earth. There were also false claims of elements that only exist in space. Nebulium and Coronium turned out to be familiar elements at unfamiliar densities and hitherto unknown (low) densities.

10

Sci-fi shows are crap when it comes to science for the most part. If they need to invent some substance with properties that no real substance has, they’ll just make it up and give it a sciency-sounding name. If pressed, sometimes writers will claim that their fake substances are really alloys of real substances combined in some unknown way.

11

If you disturb an atom, you can knock off some of the electrons. Usually, this is done just by heating your sample; you can also use high-frequency light or other methods. When you do this, the atom gains a charge.

If you heat up a hydrogen atom, you can give it a certain charge, no more nor less. We call that charge +1. If you heat up helium, you can give it this same amount of charge, and if you heat it up more, you can give it exactly twice as much, but no other amount. In other words, you can give it a charge of +1 or +2. Likewise, you can give lithium a charge of +1, +2, or +3, and so on. The simplest explanation for this is that a hydrogen atom has exactly one electron, a helium atom has two, which can be knocked off one at a time, etc.

It is certainly possible that the electron is actually a composite particle of some sort, and therefore that when you knock off an electron, you’re actually knocking off two or more smaller particles. But there’s no indication at all that this is true, and even if it is, it’s certainly very difficult to separate those particles, so one can still call an electron a particle.

By definition, two atoms are the same element if they have the same amount of protons, so for every number of protons, there is one and only one element. We have discovered all of the elements corresponding to numbers from one to past a hundred. The only way you could get any other elements would be to go out to even higher numbers, or to have a fractional number of protons. Although protons are composite particles made up of three quarks, and a quark might therefore be said to be a third of a proton, all indications are that it’s absolutely impossible to separate out individual quarks. And for elements higher than 100, some are more stable than others, but even at best, you’re looking at half-lifes of a few seconds, so we shouldn’t expect to find any in deep space unless we stumble across some natural phenomenon which is continually producing them. Your best bet for finding non-Earthly substances is to suppose some new form of a known element or combinations of known elements (a different isomer, say, or a new chemical compound), or a substance which is so unlike familiar materials that it is not made up of atoms at all.