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78

Based on your description, I may have found the article you originally saw, or at least one very similar. Researchers from Dartmouth College published a paper$\mathrm{^1}$ in which they report, among other things, the results of viewing sunlit white paper through two 3 meter lengths of plexiglass; one filled with $\ce{H2O}$ and one with $\ce{D2O}$. Sure ...


65

This does seem to be the case. I don't have images of the different types of water, but I did find this overlaid IR-visible spectrum of water and heavy water: As you stated, the presence of deuterium shifts the absorbance spectrum of heavy water further into the IR region, rendering it colorless. The website I found this on (http://www.webexhibits.org/...


33

Not quite, an isotope has same number of protons ($ A- N = Z = \mathrm{constant}$), but a different number of neutrons ($\mathrm N$ varies; e.g. $\ce{^3_\color{red}{1}H}$ and $\ce{^2_\color{red}{1}H}$, or $\ce{^235_\color{red}{92}U}$ and $\ce{^238_\color{red}{92}U}$ are isotopes). An isobar has a fixed number of total nucleons ($Z + N = A = \mathrm{constant}...


31

Yes, it has a lot to do with mass. Since deuterium has a higher mass than protium, simple Bohr theory tells us that the deuterium 1s electron will have a smaller orbital radius than the 1s electron orbiting the protium nucleus (see "Note" below for more detail on this point). The smaller orbital radius for the deuterium electron translates into a shorter (...


31

Harold Urey and George Murphy used spectroscopy to identify deuterium late in 1931, announcing it at the 1931 Christmas meeting of the American Physical Society. Picking up out of 'From Nuclear Transmutation to Nuclear Fission, 1932-1939" by Per F. Dahl: If anything, the naming of the new isotope proved more problematic than its isolation. At a special ...


29

Approximately 99.3% of uranium on Earth is the $\mathrm{^{238}U}$ isotope, and this specific isotope has an atomic mass of $\mathrm{238.05\ u}$, where $\mathrm{u}$ is the atomic mass unit, equivalent to 1/12 the mass of a $\mathrm{^{12}C}$ atom. Including the other isotopes to obtain the average atomic mass drags the value down a little, but it still ends up ...


28

Yes, there are seven known isotopes of hydrogen, though only two ($\ce{^1H}$ and $\ce{^2H}$) are stable with respect to nuclear decay, and only three ($\ce{^1H}$, $\ce{^2H}$ and $\ce{^3H}$) exist/can be made in enough quantities to be relevant outside of nuclear physics. All other hydrogen isotopes have extremely small half-lives. The next most stable ...


26

In addition to the reasons ste listed, the isotopes of hydrogen have the greatest differences in mass compared to other elements. Consider that deuterium is twice as heavy as protium, and tritium is three-times as heavy as protium. Isotopes of all elements can be used in kinetic isotope experiments. The dramatic differences in mass among the hydrogen ...


26

All possible arrangements of $\ce{Br2}$ molecule: $\displaystyle 79 + 79 = 158$ $\displaystyle \color{red}{79 + 81} = 160$ $\displaystyle \color{red}{81 + 79} = 160$ $\displaystyle 81 + 81 = 162$ The amount of $\ce{^{79}Br}$ and $\ce{^{81}Br}$ in nature is roughly the same, thus each permutation is equally probable. There are two arrangements that lead to $...


25

Yes, $\ce{T2O}$ has been prepared and is available in significant quantity. When relatively pure, the energy released by the radioactive decay process is so intense that $\ce{T2O}$ will boil. It must be transported in a shielded, cryogenic dewar. A significant difference between compounds containing an element bonded to protium, deuterium or tritium is ...


24

For the reasons explained in New point of view on the meaning and on the values of $K_\mathrm{a}(\ce{H3O+, H2O})$ and $K_\mathrm{b}(\ce{H2O, OH-})$ pairs in water Analyst, February 1998, Vol. 123 (409–410), the $\mathrm{p}K_\mathrm{a}$ of $\ce{H3O+}$ in $\ce{H2O}$ and the $\mathrm{p}K_\mathrm{a}$ of $\ce{D3O+, D2O}$ are undefined. The entire point of the ...


22

IR-3.3.1 Isotopes of an element The isotopes of an element all bear the same name (but see Section IR-3.3.2) and are designated by mass numbers (see Section IR-3.2). For example, the atom of atomic number 8 and mass number 18 is named oxygen-18 and has the symbol $\ce{^{18}_{}O}$. IR-3.3.2 Isotopes of hydrogen Hydrogen is an exception to the rule in Section ...


17

The relative natural abundance of isotopes is not the same everywhere. Depending upon what you mean by "everywhere", there are two cases to consider. Extraterrestial Dust from before the sun was formed (stardust, presolar grains) has a very different elemental and isotopic composition than that found on earth. Depending where a star is in its life cycle ...


17

The short answer is nuclear binding energy, which is the energy needed to disassemble an atom into its subatomic parts (or in some cases the energy released when this happens). The binding energy is a consequence of the strong and weak nuclear forces that hold atoms together. Where does this energy come from? It comes from the mass of the nucleons! What? ...


17

I think there are two reasons. First, it is more convenient to categorize them under the actual element-name to which they belong. If I say "15-Beryllium" everyone knows immediately, what I'm talking about. If we add hundreds of isotope-names, it would be quite a mess. Leading to the second reason: Xenon for example has over known 30 isotopes. There are just ...


17

Your chemistry teacher is making a few simplifications there that make the statement false on a black-and-white true-and-false scale. Protons would repel each other electrostaticly due to their same charges. Neutrons interact with protons by the so-termed strong interaction (because it is stronger than the weak interaction; props to physicists for inventing ...


16

Water has formula H2O. Oxygen has 3 stable isotopes (99.76% 16O, 0.039% 17O, 0.201% 18O), and hydrogen has two (99.985% 1H, 0.015% 2H). Thus, there are 9 natural isotopic configurations for water: 3 possibilities for oxygen, multiplied by 3 possibilities for 2 hydrogens with 2 possible isotopes. Out of those 9 possible configurations, only 4 have a natural ...


16

Isovalent isotopes will have the same force constant. However the different masses of the isotope will affect the position of the vibrational state in its potential well. You can rationalise the difference in well depth briefly using the vibrational frequencies of a classical oscillator as the harmonic approximation to the asymmetric well for low lying ...


15

It depends how pure you want the $\ce{D2O}$ to be and what you consider simple :) Electrolysis of water strongly favors "H" being converted to hydrogen gas rather than "D", by a factor of about 8 to 1 (depending upon the electrodes). Inexpensive Equipment for the Preparation and Concentration of Pure $\ce{D2O}$ Ohio Journal of Science volume 41, number 5,...


15

For elements with no stable isotope (i.e. Francium, Radium, and Actinium), the atomic mass is chosen to be that of the longest lived isotope. More generally, the masses for stable elements are reflective of the natural abundance of each isotope in a sample of the element. Sodium has more than one isotope, so the statement is not really true, though only ...


14

This is an interesting question and depending on how you define bond strength the answer is different. Let us for simplicity consider only diatomic molecules and let us assume that the electronic potential between the two atoms is well described by a Morse potential \begin{align} V(r) &=D_e \left( 1 - \mathrm{e}^{-a(r-r_e)} \right)^2,& \text{with } ...


14

You have two equations and 3 unknowns, so you can't solve it with just that. Say a, b, c are the fractions (as a decimal) of each isotope... $$ a(x) + b(x+1) + c(x+2) = (x+\frac{1}{2}) $$ $$a + b + c = 1 $$ The 4:1:1 solution works. Another that works is 3:0:1. Another is 7:4:1. There are infinitely many solutions.


13

This is an interesting question and you raise a number of points, let's step through them. A consequence of this is that relative atomic masses of elements mined—those with two or more stable isotopes—will no longer be faithful to our current periodic table. But this is already happening. $\ce{^235U}$ constitutes 0.72% of uranium found on earth and ...


13

As already stated, the system of equations is underdetermined. But we can get the range of possible solutions. Starting with \begin{equation} xM + y(M+1) + z(M+2) = M + \frac{1}{2} \end{equation} and using the normalization constraint \begin{equation} x + y + z = 1 \end{equation} we get \begin{equation} (x+y+z)M + y + 2z = M + \frac{1}{2} \\ y + 2z = \...


13

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 ...


12

No, deuterium is completely stable. I found the answer at Hyperphysics, and it has to do with the mass energies of the products and reactants of this hypothetical reaction. The decay of deuterium would be $$\ce{D -> P + N + e + \bar{\nu}}_e$$ where $\ce{D}$ is deuterium, $\ce{P}$ is a proton, $\ce{N}$ is a neutron, $\ce{e}$ is an electron and $\ce{\bar{\...


12

When comparing isotopes, the different nuclear masses control the bond length and bond strength. The radius of the $n^\text{th}$ Bohr orbit is given by $$r_{n} = {n^2\hbar^2\over Zk_\text{c} e^2 m_\text{e}}$$ where $Z$ is the atom’s atomic number, $k_\text{c}$ is Coulomb’s constant, $e$ is the electron charge, and $m_\text{e}$ is the mass of the electron. ...


12

This early paper reports that acidic compounds (phenols, carboxylic acids, and others) are noticeably more dissociated in $\ce{H2O}$ than $\ce{D2O}$. Since water (protio or deuterio) is just another example of a weak acid, it is not unreasonable to expect $\ce{H2O}$ and $\ce{D2O}$ to follow this pattern. This would suggest that the equilibrium constant in ...


11

The differences in molecular mass stem from two sources: Nuclear binding energy The definition of the atomic mass unit and Avogadro's number (and thus the g/mol), is the mass of one atom of the carbon-12 isotope $\ce{^{12}_6 C}$. 1 amu = $\frac{1}{12}$ the mass of one atom of $\ce{^{12}_6 C}$ and the g/mol unit is based on the definition of Avogadro's ...


11

Whatever the isotopes are for asteroidal material (and they are mostly close to those seen down here on Earth), they are contained in the 5 to 100 tons of meteoritic material that falls onto the Earth's atmosphere (and thus filters down to us on the surface) every day. It will be a long time before the cumulative pollution from asteroid (or lunar) mining can ...


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