60 votes
Accepted

Why do we use helium in balloons?

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 ...
49 votes

Why do we use helium in balloons?

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 ...
40 votes

Does the mass of sulfur really decrease when dissolved in water and increase when burnt?

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 "...
  • 30.1k
34 votes

Are there any good examples of commonly ingested molecules that contain particular toxic individual elements?

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 ...
  • 5,487
23 votes
Accepted

Will adding up protons and electrons (without neutrons) create a new element?

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 ...
  • 64.8k
21 votes

If you put two blocks of an element together, why don't they bond?

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 - ...
  • 16.9k
21 votes

"Estrontium" on poster

"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 ...
  • 9,157
20 votes

Will adding up protons and electrons (without neutrons) create a new element?

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. ...
  • 443
18 votes
Accepted

Is the relative natural abundance of isotopes of an element the same everywhere?

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 ...
  • 82.5k
17 votes
Accepted

Why is beryllium transparent to x-rays?

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 ...
  • 5,487
16 votes
Accepted

What makes carbon special and versatile?

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 ...
  • 82.5k
16 votes
Accepted

If radium has such a long half-life, how can radon possibly be a threat to us?

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 ...
16 votes
Accepted

Is hydrogen bonding generally defined to include only three period two elements?

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 ...
  • 39.1k
16 votes
Accepted

Why are some elements more abundant than others in the universe?

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 ...
  • 1,635
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 ...
  • 33.6k
16 votes
Accepted

Can osmium react with oxygen at room temperature?

From Encylopedia Britannica: Of the platinum metals, osmium is the most rapidly attacked by air. The powdered metal, even at room temperature, exudes the characteristic odour of the poisonous, ...
  • 19.4k
15 votes
Accepted

Why is a temporary name given to an element with an atomic number above 100?

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 ...
14 votes
Accepted

Why is osmium the densest known element?

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 ...
  • 82.5k
14 votes

Memorizing the periodic table

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. ...
  • 241
14 votes
Accepted

Why is Astatine monoatomic?

One key problem with astatine is that it's incredibly unstable. There are no known stable isotopes, and the longest-lived has a half-life of ~8 hours. So no one has been able to (yet) prepare enough ...
14 votes
Accepted

What are the most extreme chemicals?

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 ...
14 votes

What is the difference between "molecular mass", "average atomic mass" and "molar mass"?

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 ...
  • 66.8k
14 votes
Accepted

Identification: was this gallium or mercury from broken thermometer?

Gallium, and Galinstan have the ability to wet glass, while mercury does not. So it's most probably gallium (or Galinstan).
  • 6,824
13 votes
Accepted

Elements other than carbon that can form many different compounds by bonding to themselves?

Is carbon the only element that can do this? No, carbon is not the only element with such characteristics. If not, then what are the other elements can also do this? There is a whole number of ...
  • 486
12 votes

How were the elements discovered before modern technology?

Modern day scientists rely on technology and advanced nuclear physics. But in absence of these advances, how were ancient scientists able to discover them? In many cases, they weren't - the ancient......
  • 10.1k
12 votes

Is there a way to contain fluorine gas for long term so that it can be visually observed?

As @JonCuster mentions, some materials are pretty resistant to fluorine gas at room temperature. But out of curiosity, I checked Theodore Gray's website. He's made an effort to have a "periodic table"...
12 votes
Accepted

Is it possible for Hydrogen to lose its electron?

Hydrogen can lose an electron meaning it can be in the +1 oxidation state. However, just like any other cation or anion it never occurs free in condensed matter, it always is in contact with solvent ...
  • 20.9k
12 votes
Accepted

Memorizing the periodic table

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 ...

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