how do scientists find the percent abundance of isotopes?

Answer 1

You can use a mass spectrometer. This device is formed of five chambers thus allowing 5 phases:
1. Vaporization: the sample that contains all the isotopes is heated till it becomes a vapor
2. Ionization: the sample is passed over a a metal wire that is heated soo much that it loses electrons. The free electrons are attracted to a metal plate on the other side of the ionization chamber. As they move in a stream through the vaporized sample, they knock off one elctron from each atom of the sample making them cations (positive ions)
3. Acceleration: the ionized sample is passed through two or three magnetized plates that accelerate the ions (all to the same speed) and focus them into a thin beam.
4. Deflection: the sample of (now) cations is passed through a curved tube that is surrounded by two magnets creating a magnetic field. Because the cations are charged, the magnetic field can affect their path. The heavier isotopes will fall to the side, and light isotopes will be deflected extremely. Only one kind of isotope will be deflected correctly to pass through the curved tube. By varying the magnetic field, eventually all the isotopes will pass through the tube to the last chamber.
5. Detection: In this final stage, the various samples, at various times, will hit a neutral metal plate and cause it to lose an electron thus turning the cations back into atoms. The loss of the electron will allow a flow of electrons in the neutral plate so that it can gain back it's neutrality. The flow of electrons will cause a current that can be detected by a computer.
--- The computer will then create a graph. By studying the graph, scientists can see how much of each isotope was detected and thus by dividing the number of each isotope over the total number of different isotopes detected, and multpilying that number by 100, they can find the percent abundance of isotopes. Then again, there are other graphs that do the calculations themselves and then just give the scientists the results.
--- below are two websites for mass spectrometry. The "how it works" website clarifies the first part of my answer with a picture of a mass spectrometer and the various parts of it and the second website shows graphs of the mass spectra of elements (as you can see, the graphs shown here directly give the % abundance so you don't have to do any calculations, unless you want to find the average molar mass of the element - which isn't what you asked! haha)
hope i helped

Answer 2

In the early days of chemical research (19th century), chemists had to rely on the fact that heavier isotopes generally engage in chemical reactions more slowly than lighter isotopes. They would do experiments like allowing a large volume of water to almost evapourate, then weigh the remaining water and measure its volume (it would contain a much higher proportion of "heavy water"). Now that chemists have access to more sophisticated equipment (like mass spectrometers) it's much easier and more accurately done.

In special cases where certain isotopes are radioactive and others are not (such as carbon), the isotope proportion can be measured over time.

Answer 3

as far as I know it just comes from empirical evidence, that is, scientists just measure random atmic collections and assume that those ratios are basically valid unless proven otherwise.

And to the first poster, if you knew anything about chemistry at all, you would understand why this is a valid question for which the answer might not actualy be mentioned in a textbook

Answer 4

these days we use Mass Spec

Answer 5

I don't know Read the chapter.

When you find out let me know to. kthxbai