Researchers made a breakthrough that could change the foundation of chemistry as we know it.
The team made prediction in how one could compress rock salt to form new compounds. The compounds in question confirmed the accuracy of the lead researcher's methodology for predicting an object's properties, a Stony Brook University news release reported.
"I think this work is the beginning of a revolution in chemistry," lead researcher Artem R. Oganov said. "We found, at low pressures achievable in the lab, perfectly stable compounds that contradict the classical rules of chemistry. If you apply the rather modest pressure of 200,000 atmospheres -- for comparison purposes, the pressure at the center of the Earth is 3.6 million atmospheres -- everything we know from chemistry textbooks falls apart."
Standard modern textbooks teach that sodium and chlorine have completely different electronegativities, meaning they have no choice but to form an "ionic compound with a well-defined composition." Sodium has a +1 charge while chlorine has a -1. Since sodium gives away an electron and chlorine obtains one the only possible combination of the two would be NaCl (rock salt).
"We found crazy compounds that violate textbook rules -- NaCl3, NaCl7, Na3Cl2, Na2Cl, and Na3Cl," Weiwei Zhang, the lead author and visiting scholar at the Oganov lab and Stony Brook's Center for Materials by Design, said. "These compounds are thermodynamically stable and, once made, remain indefinitely; nothing will make them fall apart. Classical chemistry forbids their very existence. Classical chemistry also says atoms try to fulfill the octet rule -- elements gain or lose electrons to attain an electron configuration of the nearest noble gas, with complete outer electron shells that make them very stable. Well, here that rule is not satisfied."
Oganov theorized that if he compressed NaCl and metallic sodium in a heated diamond anvil cell and found it would create sodium-rich Na3Cl. He also suggested that if NaCl was compressed with pure chlorine it would create NaCl3.
Experiments by Alexander F. Goncharov of Carnegie Institution of Washington confirmed these theories.
The compound Na3Cl has an exceptionally interesting structure according to Oganov. It is made up of "layers of pure sodium"that act as insulators and conduct electricity.
"For a long time, this idea was haunting me -- when a chemistry textbook says that a certain compound is impossible, what does it really mean, impossible? Because I can, on the computer, place atoms in certain positions and in certain proportions. Then I can compute the energy. 'Impossible' really means that the energy is going to be high. So how high is it going to be? And is there any way to bring that energy down, and make these compounds stable?" Oganov said.
The team made their finding by breaking the rules of chemistry.
properties and levels of stability.
"We have learned an important lesson -- that even in well-defined systems, like sodium chloride, you can find totally new chemistry, and totally new and very exciting materials," Oganov said. "It's like discovering a new continent; now we need to map the land. Current rules cannot cope with this new chemistry. We need to invent something that will."