# Tag Info

12

Periodic tables of elements (PTEs) are often abused by designers. Books are more trustworthy as long as they are written by scientists. Long story short, the second notation $(\ce{^{12}_{6}C})$ is the correct one. There is an easy to remember AZE notation: $^A_Z\ce{E}$. I suspect the PTE you were looking at lists standard (averaged) atomic weights of the ...

11

Here is the "periodic table for biomolecules" (leaving out hydrogen, please ignore silicon): The pie chart shows the isotope distribution. Of the elements C, N O, P, S and H, sulfur has the highest abundance minor isotope (around 4%). On the other end of the spectrum,phosphorous is a mono-isotopic element, with just one stable isotope. There is an ...

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According to the international standard ISO 80000 Quantities and units – Part 9: Physical chemistry and molecular physics (corrected in Amendment 1, 2011-06-01), the attached subscripts and superscripts have the following meanings. (…) The nucleon number (mass number) of a nuclide is shown in the left superscript position, as in the following ...

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Most periodic tables quote the molar mass of an element as the average mass of the element given the natural abundance of the isotopes. Chlorine, for example, has a standard atomic weight of 35.45 which is a weighted average of ~75% 35Cl and ~25% 37Cl, the two common isotopes. But isotopes of hydrogen and oxygen are rare. So the vast majority of water ...

7

The half-life of $\ce{^{89}Sr}$ is 50 days compared to a half-life of 29 years for $\ce{^{90}Sr}$. So a large enough dose of $\ce{^{90}Sr}$ to be useful would leave the patient radioactive for the rest of his/her life. Edited for use of $\ce{^{89}Sr}$. In a comment Karl pointed out that the isotope is used to treat bone cancer.

6

You have already got an answer by Dr. Karsten, but let me add that modern mass spectra have become sensitive beyond imagination. Secondly, the resolution of mass is no longer a problem. Fourier transform ion-cyclotron resonance mass spectrometer (a mouthful) is extremely sensitive to mass differences. Yes, if you have a low concentration, your main analyte ...

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There is a shell structure within the nucleus also. So the neutron/proton ratio varies from 1:1 for the light elements to 1.5 for the heavy elements. Note: I ripped off the image from another website. Not sure where they got it from...

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Chemically speaking compounds containing isotopes are very similar but not exactly similar Broadly when compounds contain different isotopes of the same element (say different isotopes of oxygen) their reactivity is the same. But this is a little over broad. There are subtle and (usually) small differences and these can show up as small differences in ...

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There are two approaches to measuring kinetic isotope effects. One is to have two completely separate, isotopically pure systems, one heavy, and one light. In each system you can measure the rate of the reaction however you want. You don't have to be able to measure the rate in an "isotopically resolved" way, just measure the bulk rate. Each of your ...

4

Different periodic tables show the atomic number above, below, or next to the element. They don’t show the mass number, usually, but the atomic weight (not an integer). There is a type of table, for example the Karlsruher Nuklidkarte, that shows all observed isotopes, and this type of chart does show mass numbers as well. In the picture, the isotope chart ...

3

There are 5 ways to choose the central atom. Choosing the possible combinations of the other 4 items from 6 isotopes is complicated as this article explains. But it provides a formula for combinations with repetition that gives the answer of 126. This implies that there are 630 distinct isotope combinations in the molecule (assuming that we can ...

3

It's impossible to find isotopic composition of a compound with a molecular weight containing only one decimal point ($\pu{18.\underline{0} g mol-1}$). Typically, 6th decimal place is required in order to refine percentage of each isotope. Symbols themselves (such as $\ce{H}$ and $\ce{O}$) don't carry any additional information except atomic number $Z$. For ...

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On 2019-11-29 Ben Krasnow uploaded a YouTube video DIY mass spectrometer measures potassium in dietary salt substitute showing an outstanding construction of a mass-spec apparatus in his home shop based on the articles by Dewdney [1] and Stong [2] with some variations and improvements, like altered electrical scheme and increased emission current. The main ...

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No, isotopes are always an issue, even just for hydrocarbons. $\ce{^13C}$ may only be 1.1% of most natural pools of carbon atoms, but as molecules get larger and larger, i.e. as they consist of more and more carbon atoms, the probability that at least one of the carbon atoms in a large molecule is carbon 13 becomes much larger. Molecules with more than ~...

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As a general matter, it seems possible that neutron isotopes are actually not physically similar to their elements, since, for example, a given isotope might not be stable. It was very well known (pre-1940s) that the number of protons (Z) distinguish one element from the other. If we talk about the simplest element with Z=1, whether it contains 0, 1 or 2 ...

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Not by a homebuilt mass spectrometer, you can't. At least not with a reasonable amount of effort. A mass spectrometer is a very complicated and sensitive charged-particle optics instrument. A useful mass spectrometer for materials that are not a gas or vapor at near room temperature is far more complicated and expensive than that. A mass spectrometer ...

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