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58

As other answers have noted, the only gas lighter than helium is hydrogen, which has some flammability issues that make it more difficult to handle safely than helium. Also, in practice, hydrogen is not significantly "lighter" than helium. While the molecular mass (and thus, per the ideal gas law, the density) of hydrogen gas is about half that of helium, ...


48

Nobody really knows. Using the naive Bohr model of the atom, we run into trouble around $Z=137$ as the innermost electrons would have to be moving above the speed of light. This result is because the Bohr model doesn't take into account relativity. Solving the Dirac equation, which comes from relativistic quantum mechanics, and taking into account that the ...


48

Actually, hydrogen is the only gas that is lighter than helium. However, it has a very big disadvantage: It is highly flammable. On the other hand, helium is almost completely inert - this is why it is very much safer to use the latter. What might happen when you use hydrogen instead of helium was impressively proven by history when the "Hindenburg" ...


39

Upon reading the answers on Quora (thanks S007 for pointing that out) I realized this trick question is a lousy play upon two somewhat peculiar features of sulfur: When submerged in water (not "dissolved", mind you, for sulfur does not dissolve), its apparent weight becomes less, thanks to Archimedes and the buoyancy force. This is indeed true of any ...


34

To expand on @BelieveInvis's answer -- in the early 19th century, when the Royal Society was really in the swing of things, the dominant language of scholarship was still Latin. Since Latin didn't have words for the new metallic elements, new words were coined from the existing terms for the substances and given Latinate endings. From the OED's entry on -...


29

Table salt! What would be worse than putting sodium (it can spontaneously combust if you get it wet) and chlorine (used as a war gas in WWI) all over your food? Then there's water which always contains some $\rm OH^-$ (an active ingredient in Drano) and $\rm H^+$ (that stuff eats through metal, man). Although those aren't elements. And hiding inside every ...


23

Yes and no. Elements are defined by the number of protons only. It does not matter if (say) a carbon nucleus has six or seven (or eight) neutrons, they will all react the same.* With that, to create new elements, you would need to get up to some 115 or so protons fused together. But there is a reason for neutrons: all the positively charged protons in the ...


22

Diamond (carbon) does not melt at 1 atm. It sublimes to vapor. Using carbon's theoretical phase diagram below (from Wikimedia), "liquid diamond" could be achieved at about 10 GPa (99 thousand atmospheres) and 5000 K (4700 °C). Edit: In fact, heating up diamonds at 1 atm turns them into graphite first. Only further heating would cause sublimation, as ...


21

Neptunium (93) and plutonium (94) were so named because they followed uranium (92) on the periodic table. Uranium was named after Uranus. German chemist Martin Heinrich Klaproth discovered uranium in 1789, eight years after William Herschel discovered Uranus. At the time, uranium was the densest element known and Uranus was the farthest planet from the sun ...


20

Jan's answer is correct. I will try to fill in a few details about why neutrons are essential to creating stable nuclei. All stable isotopes excepting Hydrogen-1 have neutrons in their nuclei. Hydrogen, for example has two stable isotopes: The first simply has a proton with no neutrons in the nucleus, while the second, often called Deuterium has a proton ...


20

Why, when you bring the two bars together so that they touch each other, do they not instantly bond with each other forming one larger bar or block? ... Why do we need to 'weld' two bars together - why don't they just bond on their own? The problem is generally one of two things: gases (air) or metal oxides get in the way. You can actually bond two pieces ...


20

"Estrontium" is not used as an element name in any language. It appears that the error traces to a single user by the name of Alejo Miranda (listed as from Ecuador) who has posted a large collection of periodic tables and individual element clip art to shuttersock, iphoto, etc. in which "estrontium" is incorrectly used as the English name for strontium. The ...


17

The -ium suffix is a Latin suffix which forms abstract nouns, thus it is used to form chemical elements' name from its naming origin, such as minerals (calcium from calx) or person names (gadolinium).


17

Is Astatine a non metal or a metalloid? Unknown According to the Wikipedia article on astatine, the longest-lived isotope has a half-life of 8.1 hours. The element is so radioactive that large samples would melt and vaporize under the heat generated by its own radioactivity. Such behavior makes it difficult to assess whether astatine has the appropriate ...


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 ...


16

This is a Google ngram of the usage of the words:iodine, carbon, nitrogen, zinc and Iodine,Carbon, Nitrogen, Zinc (not at the beginning of the phrase). There is no historical trend, at least not an usage of an archaic form (we can see that the maximum usage of the capitalized element name is from 1900 to 1960 but normalized to the overall usage is steady). ...


16

Asked and answered, but this is a good place to include other astronomically named elements: cerium named after the asteroid Ceres (or the Roman goddess of agriculture) helium from the Greek helios or "Sun" mercury OK, named after the Roman god, but so was the planet palladium named after the asteroid Pallas, discovered the year that Pd was first isolated ...


16

There are two key factors that account for the ubiquity of carbon compounds. Bond strengths: Look at the following table of bond strengths and notice how the strength of both carbon-carbon single and double bonds is much greater than the bond strengths found in other molecules. \begin{array}\hline Typical~Single ~Bond~ Dissociation ~Energies~ (kcal/mole)\\ ...


16

There are two factors here: Radon is a gas and can thus enter the body very easily, through inhalation. $\ce{^222Rn}$ and its first 4 decay products are extremely radioactive, with halflives of miliseconds to a few days, releasing alpha and beta radiation. When the two are combined, we have a problem. Even if the quantity is low, inhaling radon places an ...


16

The amount of X-rays absorbed by an element depends on the size of its atoms (its absorption cross-section, specifically, as affected by the size of core orbitals that contain electrons that can be excited by X-ray absorption, and the number of electrons in those orbitals) and how many atoms are packed into a given volume. Big atoms that are close together ...


15

The systematic element names refer to a temporary name and symbol for hypothetical and newly synthesized elements. Because of naming controversies in the past, these names were introduced by the IUPAC to discuss the elements without ambiguity. After the discovery is confirmed, they receive a permanent name. The IUPAC states in the red book this controversy ...


15

WHAT MAKES HYDROGEN ABUNDANT IN UNIVERSE: After few minutes of creation of the universe, protons and neutrons began to react with each other to form deuterium, an isotope of hydrogen. Deuterium, soon collected another neutron to form tritium. Rapidly following this reaction was the addition of another proton which produced a helium nucleus. Sources say ...


14

I don't think there is any such traditional definition requiring $\ce{N}$, $\ce{O}$ or $\ce{F}$. For example, in table 7 and the discussion thereof in Hydrogen Bonding Annual Review of Physical Chemistry Vol. 22: 347-385 the hydrogen bonds in the following species are discussed: $\ce{ClHCl^-}$ $\ce{BrHBr^-}$ $\ce{IHI^-}$ $\ce{BrHCl^-}$ as well as related ...


14

Densest gas Densest element Greatest range between melting and boiling temperature Highest melting point Lowest solubility product constant Most dangerous: Is there any substance that's a 4-4-4 on the NFPA diamond?. But also, don't forget that the NPFA diamond doesn't even classify ClF3 as flammable (though everything else is flammable in it) and by any ...


14

Atomic mass refers to the average mass of an atom. This has dimensions of mass, so you can express this in terms of daltons, grams, kilograms, pounds (if you really wanted to), or any other unit of mass. Anyway, as you said, this is an average of the masses of the isotopes, weighted by their relative abundance. For example, the atomic mass of $\ce{O}$ is $15....


14

Gallium, and Galinstan have the ability to wet glass, while mercury does not. So it's most probably gallium (or Galinstan).


13

The density of an element is related to how many atoms can be placed in a given volume and the weight of the nuclei. Therefore, the smaller the atomic radius of an atom and the higher the atomic number of the nucleus, the greater the density of the element. The very small atomic radius of osmium results in a small metal-metal separation. This small atomic ...


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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