# Tag Info

## Hot answers tagged periodic-table

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

The short answer is that you can find a power-law fit ($1.61Z^{1.1}$) with low average error. I'd never really thought about it much, but after downloading the IUPAC Atomic Weights, I decided to do some curve fitting. Here's a linear fit between atomic number and atomic mass: As you say, the fit isn't very good for small $Z$, but the overall fit isn't bad ...

19

I think it's also important to mention relativistic effects here. They already start becoming quite visible after $Z=70$, and $\ce{Ra}$ lies a good bit after that. In very heavy atoms, the electrons of the $\ce{1s}$ orbital (actually, all orbitals with some electron density close to the nucleus, but the $\ce{1s}$ orbital happens to be the closest and ...

17

Surprisingly, I learned that there are also usages for orbitals g,h,i and even j. Actually, the letter "j" is not used, so it is s, p, d, f, g, h, i, k, l, etc. The higher angular momentum orbitals do enter the domain of science, due to excited states of atoms. Transitions to and from excited states are observable through atomic spectroscopy. For ...

16

Blocks in the periodic table should not be mixed up with groups (like noble gases). The reason why Helium is considered a noble gas is because its outermost (and at the same time only) shell is fully occupied by its 2 electrons. When you look at the electron configurations in the PTE you can see that the first element which happens to have an occupied p-...

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Please do not underestimate the scientists of 19th century. They were as creative, intelligent and perhaps more genuinely dedicated to science than the scientists of the 21st century. Spectroscopy was the tool of the trade to identify and verify that a given substance is not a mixture. The original reference which established that Didymium was a mixture is ...

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On the contrary, zinc(I) compounds do exist, though they are rare, and relatively unstable. Most zinc(I) compounds contain a $\ce{[Zn2]^{2+}}$ core, which is analogous to the $\ce{[Hg2]^{2+}}$ cation. The $\ce{[Zn2]^{2+}}$ ion does, however, rapidly disproportionate into zinc metal and zinc(II), and has only ever been obtained by cooling a solution of ...

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

There isn't really much sense in memorizing the periodic table. The elements you often use you will know them by heart after a while. And you can always use a table when you need it for the others. That being said if you really want to do it, mnemonics are probably the best solution to memorizing the whole table. You can find some here : https://www....

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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

The Periodic Table arranges elements in blocks as each type of orbital fills with electrons - $s,p,d,f,g,h$. Alkali metals and alkaline earths are $s$-block filling (but could be one $s$-block slot). $p$-block six electrons to fill are trelides, tetralides, pnticides, chalcogenides, halides, inert gases (but could be one $p$-block slot). Transition metal $... 12 Since OP is still in the high school, I'll try to explain it simply as possible using mathematical manipulation (hoping OP is more familiar with mathematics than chemistry). Both gold and platinum consist of same crystal packing called body-centered cubic, which is illustrated in following diagram: Crystal studies of both gold and platinum has revealed ... 12 There is no theoretical limit to the number of rows, but... On one hand, as Tom Lehrer states, there may be many others but they haven't been discovard. On the other hand, after all s, p, d, f orbitals are filled in the seventh period, there might be a new row, or there might be an extension of the seventh row, as a new type of orbital (g? Anyone know it ... 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 ... 11 You can memorize the periodic table in one night, simply by emulating best-practice memorization techniques and doing what memory experts do. Common sense, right? Memory experts and world champion memory ‘athletes’ activate the enormous natural power of their visual memory by using visualization and association mnemonic techniques. That’s a fancy way of ... 11 So if that is the case, shouldn't period 3 have more elements, since it can hold up to 18 electrons, and therefore it can have up to 18 more protons from the largest atomic number element in period 2? Indeed, elements of the same period have the same number of electron shells, but the "problem" is that in accordance with the Madelung/Janet/Klechkowski ... 11 In 1978, the IUPAC Commission on the Nomenclature of Inorganic Chemistry decided that it would be necessary to have a systematic naming for the elements with atomic number greater than 100, even for those which had not been discovered. The recommendations are as follows: The name is derived directly from the atomic number of the element using the ... 11 It might be scientifically correct but it is linguistically misleading The sentence "diamond is an element" can be seen to be misleading when compared to the sentence "diamond is an allotrope of the element carbon". Or even "diamond consists of the element carbon". The issue is that clear language should distinguish between the form and the composition of ... 11 First and foremost! Do not do this reaction unless you are properly trained and have the appropriate safety equipment. Fluorine is one of the most dangerous substances out there, and one of the presumed products,$\ce{OF2}$, is also terrifying. If you can calculate the free energy change for a reaction, you will know whether it is spontaneous. To do this, ... 10 Well, the first question to answer would be: where? The rarest element in the universe? the sun? in meteorites? on earth? in the ocean? in humans? We can tap in to the curated datasets provided by Mathematica to get the answer: Elements up to atomic number 98 have been found in trace quantities; however, the dataset does not contain any information about ... 10 This behavior can be attributed to the same phenomenon as that which causes the lanthanide contraction. The electrons in$f$subshells are very poor at nuclear shielding, so the$s$electrons in the next higher shell are closer (on average) to the nucleus than you might expect. If these electrons are closer to the nucleus, then the atom exhibits a smaller ... 10 While it's an interesting thought, I don't think it's very useful to suggest Mendeleev predicted neutrinos. It's far more sensible for it to be a curious coincidence. His suggestions of ghost-like properties similar to neutrinos (very hard to detect, tiny mass, little interaction with matter, etc) are more easily explained as an attempt to justify (properly) ... 10 The pattern is better expressed this way: Row 1: 2 elements Row 2: 2+6 elements Row 3: 2+6 elements Row 4: 2+6+10 elements Row 5: 2+6+10 elements Row 6: 2+6+10+14 elements Row 7: 2+6+10+14 elements The reason comes down to how the electrons fill the available energy levels. The thing that differentiates one element from another is the proton number, and ... 10 One attempt to order chemical elements was Döbereiner's system of triades, published in Annalen der Physik und Chemie, back in 1829 (doi 10.1002/andp.18290910217 with Wiley); or (open access with Gallica). Although an actual view into his paper permits the speculation he was not using the atom masses we know today; rather than using specific weight and ... 10 The letters are related to the electron orbitals, which were originally observed through spectroscopy. The lines shown in the spectroscope were named sharp, principal, diffuse and fine (or fundamental). With a strong magnetic or electrostatic field, these separate into one, three, five or seven lines, or energy levels. There can be up to two electrons (with ... 8 One could do it in the following way. The atomic number$Z$can be determined by examining the x-ray spectrum of an atom. The frequency$f$of the so-called K-alpha line is related to the atomic number$Z$by Moseley's law $$\sqrt f = k_1 \cdot \left(Z - k_2\right) \, .$$ The atom is electrically neutral, so the number of electrons is obviously ... 8 Because if you put lanthanides and actinides in to the Periodic Table like transition metals, the table will be way too wide. 8 The average relative atomic mass of an element comprised of$n$isotopes with relative atomic masses$A_i$and relative fractional abundances$p_i$is given by: $$A = p_1 A_1 + p_2 A_2 + \dots + p_n A_n = \sum\limits_{i=1}^n p_i A_i$$ For example carbon: \begin{array}{lrrr} \text{Isotope} & \text{Isotopic Mass$A$} & \text{Abundance$p\$} & ...

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