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Different forms of an element which exist in the same state but have different molecular or crystalline structures. Classic examples of allotropes include diamond and graphite (allotropes of carbon), red phosphorous and white phosphorous, and $\ce{O2}$ and $\ce{O3}$ (allotropes of oxygen).

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Why does ozone have higher entropy than oxygen?

$$\ce{3O2(g) -> 2O3(g)} \qquad \Delta H^\circ (\pu{298 K}) = \pu{+142 kJ mol^-1}$$ Since the RHS of the equation contains less number of gaseous molecules, naturally I expected the $\Delta S$ to ...
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What is the standard enthalpy of formation of metallic oxygen?

I am curious as to what is the standard enthalpy of formation of metallic oxygen. I am also looking for the theoretical specific impulse of proposed metallic oxygen allotropes. The metallic oxygen ...
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Allotropes of hydrogen

Is it possible to chemically bond 8 hydrogen atoms together to form an allotrope like $\ce{H8}$?
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Does sulfur have various allotropes at room temperature?

Recently I had a question in my chemistry test that said: Which of the following nonmetals does not have multiple allotropes at room temperature? A) Oxygen B) Hydrogen C) Sulfur D) ...
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Aside from carbon, what other substances can be made “superhard”?

So diamonds are an allotrope of carbon, that is formed when carbon is put under immense pressure, right? What other elements or compounds can you make into "diamonds", as in more durable, harder ...
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Are allotropes of sulfur two different phases?

Monoclinic sulfur and rhombic sulfur are two allotropes of sulfur. In phase equilibria, part of the system that is having distinct boundary, mechanically separable and different chemical or physical ...
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Solubility of white phosphorus

Why is white phosphorus soluble in $\ce{CS2}$ but red phosphorus not? Is it something in relation with the structures of both? Please explain.
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Is Nuclear Spin Isomer a kind of allotrope?

In my book there's a question: Does $\ce{H2}$ shows allotropy ? Enlist its allotropes and their application? I pondered over different way Hydrogen can be arranged(I don't know but I have weak ...
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Is Changing between Allotropic forms a Physical or Chemical Process?

When a substance changes its alloptropic form, is this considered a physical change or a chemical change? Right now, I am thinking that it would depend on what the change was. For example, if ...
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Is ozone really a chemical element?

In our chemistry book is written that ozone ($\ce{O3}$) is a chemical element. Also our chemistry book gives a definition that agrees with that. But our teacher doesn't agree. His reasons: If ...
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Which elements exhibit allotropy?

I was just reading this article about allotropes which relates allotropy with some specific elements and also this wiki article. Also some other articles some of which relate allotropy with catenation ...
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Allotropes of Phosphorus

Something I noticed whilst revising about group 15 is that the darker the allotrope of phosphorus, the more stable it is. white/yellow – very volatile, soluble, pyrophoric red – air ...
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Why do we not see silicon in a structure like graphite?

Silicon exists in a structure similar to diamond, with 4 silicon atoms bonded to each other in a tetrahedron. Why do we not see it exist in a structure like graphite? Is it even possible to get ...
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Which allotrope of phosphorus is kinetically the most stable?

Which allotrope of phosphorus is kinetically the most stable? I ruled out white and yellow as being quite reactive. Red and black allotropes are both polymeric and comparitively less reactive. ...
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Allotropy and polymorphism

Polymorphism is defined as the ability of a solid material to exist in more than one form or crystal structure, whereas allotropy is defined as the property of some chemical elements to exist in two ...
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Allotropy in Nitrogen and Bismuth of Group 15

Which elements of Group 15 of the periodic table have allotropes? P, As and Sb have well-known allotropes: P: White, Red and Black; As: Yellow, Black and Gray (Grey); Sb: White, Yellow and Black....
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Can powdered beta-tin be made from raising the temperature of alpha-tin?

When white tin ($\beta$-tin) is cooled to a temperature below $13.2\ \mathrm{^\circ C}$, it creates the allotrope of gray ($\alpha$-tin), a gray, amorphous powder. My question is that once you have ...
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Does single-layered Aluminium Phosphide exist?

I'm currently working with the band structure of graphene and graphene-like compounds. α-Boron Nitride (hexagonal, single layer) has many interesting properties. I was wondering if the next period ...
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Is diamond an allotrope or polymorph of carbon?

Is diamond an allotrope or polymorph of carbon? When is something considered an allotrope vs a polymorph?
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Why does sulfur, but not oxygen, catenate?

Oxygen is a rather boring element. It has only two allotropes, dioxygen and ozone. Dioxygen has a double bond, and ozone has a delocalised cloud, giving rise to two "1.5 bonds". On the other hand, ...