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18 votes
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To which block of the periodic table does helium belong?

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 ...
AstronAUT's user avatar
  • 757
16 votes

How did Mendeleev know elements from compounds or mixtures?

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 ...
AChem's user avatar
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14 votes
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Spontaneity and nature of attack of fluorine gas on aluminum

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 ...
Ben Norris's user avatar
13 votes
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Confused by notation of atomic number Z and mass number A on periodic table of elements

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 ...
andselisk's user avatar
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13 votes

Why is platinum denser than gold?

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 ...
Mathew Mahindaratne's user avatar
12 votes

Calling Diamond an element?

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 ...
matt_black's user avatar
12 votes

Why are there only 7 periods in the periodic table?

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 ...
DrMoishe Pippik's user avatar
11 votes

Why is Promethium the only radioactive Lanthanide?

Lanthanoids are not generally supposed to be radioactive, with exception of mentioned very long lived radioisotopes. The longest half-life radioactive nuclides of lanthanoids ( in years ) $\ce{^{...
Poutnik's user avatar
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11 votes
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Why is UuX used as a symbol for unnamed elements on the periodic table?

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 ...
ringo's user avatar
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11 votes
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On the periodic table: Why are groups of elements organized by 'letter'

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)...
DrMoishe Pippik's user avatar
11 votes
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Is there a canonical variable for period and group?

There isn't a standard symbol. However, if you choose these current symbols, please note that "table" should be placed in upright font, not italics: correct: ...
orthocresol's user avatar
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11 votes
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Is "pentel" a real chemistry term?

Use Google Scholar (scholar.google.com/) when needed. All I searched was: pentels pnictogen, and the third search result leads to an article in Angewandte Chemie which in turn leads to the original ...
AChem's user avatar
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10 votes

What organizational methods pre-date the Periodic Table?

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 ...
Buttonwood's user avatar
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10 votes
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What organizational methods pre-date the Periodic Table?

Aaron J. Ihde's The Development of Modern Chemistry (DMC) has an entire chapter entitled "Classification of the Elements," which includes a very nice overview of the attempts before Mendeleev to bring ...
hBy2Py's user avatar
  • 17.4k
8 votes

What is the usage of orbitals more complex than f orbitals?

One use of orbitals beyond f is in computational chemistry to construct basis sets. It's important to remember that orbitals are entirely a mathmatical construct that chemists and physicists have ...
Tyberius's user avatar
  • 11.8k
8 votes

Lower melting points of zinc, cadmium and mercury

Mercury is a rather special case, which cannot be compared to Zn and Cd. Mercury (Z = $80$) belongs to the heaviest elements of the periodic table. Pekka Pyykkö's calculations have shown that nuclei ...
Maurice's user avatar
  • 28.9k
7 votes

Anomalous Electronic Configuration of Thorium

For first four actinide elements $\ce{Th}$, $\ce{Pa}$, $\ce{U}$ and $\ce{Np}$, the difference in energy between $\mathrm{5f}$ and $\mathrm{6d}$ orbitals is small. Thus in elements electrons may occupy ...
Sidhant Prasad's user avatar
7 votes

Where can I find a downloadable spreadsheet of element properties?

I found a nice json database here (it may have errors, I wouldn't know, but there are links to the original sources). Best visualised with Chernoff faces IMO, ...
baptiste's user avatar
  • 209
7 votes

Why is Thorium (At. no. 90) an f-block element at all?

The bulk metal actually does involve the $f$ orbitals, distinguishing it from what would be its congeners in Group 4 of the $d$ block. From Wikipedia: Despite the anomalous electron configuration ...
Oscar Lanzi's user avatar
  • 59.1k
7 votes

Why are there only 7 periods in the periodic table?

On the other hand, it will be difficult to synthetize elements heavier than Oganesson ($\pu{Z = 118}$) for lack of neutrons. When the number of protons increases through the periodic table, the ratio ...
Maurice's user avatar
  • 28.9k
7 votes

Why an atom is more stable when only sublevels s and p are full?

Supposedly when explaining electronegativity and stability of an element, they tell you that it is more stable if the last level is full. No "supposedly" about it. That concept is ...
John Bollinger's user avatar
7 votes

Why are there so many metals in the periodic table?

Very simply, metallicity is defined (other than in astronomy, where everything beyond He is a metal) by behavior: a shared sea (conduction band) of electrons, causing conductivity, reflectivity, etc. ...
DrMoishe Pippik's user avatar
7 votes

Is "pentel" a real chemistry term?

Group 13 and group 14 elements are trivially called triels and tetrels respectively (see previous posts- this and this). By same analogy, group 15 elements are called "pentels". pentel (...
Nilay Ghosh's user avatar
  • 26.2k
7 votes

Are there common/trivial/archaic names for any of the periods of the periodic table?

Though I don't know of terms for each row, there are a few that describe a horizontal section of the periodic table. Astronomers refer to anything other than H and He (first period) as metals, so in ...
DrMoishe Pippik's user avatar
6 votes

To which block of the periodic table does helium belong?

Helium is an s-block element with properties like those of the p-block noble gases. In a periodic table more concerned with chemical behaviour you're likely to see He in the p-block. In a table more ...
Pretty fly for a chem nerd's user avatar
6 votes

Do non-English speaking countries use the same element symbols?

Both North Korea and South Korea use the periodic table. The names, however, are different. Here is a periodic table in North Korea The title translates to "Mendeleev's atomic periodic table." The ...
CoffeeIsLife's user avatar
  • 4,284
6 votes

Electronic configuration of uranium

Nobody really knows. Our theory of how electrons are ordered in the ground states of atoms is a case of good news and bad news. And, as in human endeavors, the bad news ends up getting the headlines. ...
Oscar Lanzi's user avatar
  • 59.1k
6 votes
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Why don't elements having the same valency as Carbon bond so readily?

It's not that they don't bond readily, it's that they can't form as stable of networks as carbon. Carbon has many different allotropes, while silicon has only a few. As you can see, carbon forms ...
ringo's user avatar
  • 24.1k
6 votes
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Mendeleev's predictions

Well, guess what, even I study the exact same textbook (class 11 NCERT, from India). I had asked my teacher the exact same doubt, and the answer was: Due to its proximity with neighbouring substances,...
Abhigyan's user avatar
  • 1,667

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