\u201cThis idea that relativity is important in heavy elements has been around since the 1970s,\u201d said Lai-Sheng Wang, a professor of chemistry at Brown and the study\u2019s corresponding author. \u201cBut we show direct spectroscopic evidence that what we learned in high school about chemical bonding isn\u2019t true in heavy elements.\u201d<\/p>\n
Atoms form bonds by sharing electrons \u2014 the negatively charged particles that orbit atomic nuclei. Each atom shares one electron to form a bonding pair. The strong negative charge of the electron pair attracts the two positively charged nuclei, holding them together. Some elements share more than one electron pair, forming double or triple bonds.\u00a0<\/p>\n
The textbook picture of triple bonding involves two different types of bonds: one sigma bond and two pi bonds. The sigma bond is a strong, \u201chead-on\u201d bond that occurs along an imaginary horizontal axis between nuclei. The two pi bonds are somewhat weaker, \u201cside-by-side\u201d bonds that wrap around the sigma bond.\u00a0<\/p>\n
That picture works for lighter elements, but toward the bottom of the periodic table, where atomic nuclei get heavier, things get messy. The increased nuclear mass causes orbiting electrons to speed up to a significant fraction of the speed of light, where the rules of Einstein\u2019s theory of relativity are important.\u00a0<\/p>\n
In the relativistic regime, an electron\u2019s spin \u2014 the magnetic moment that points either up or down \u2014 and the electron\u2019s orbit are no longer independent of each other, a state known as spin-orbit coupling. That coupling changes the rules for how electrons can interact, disrupting the strict separation between sigma and pi bonds.\u00a0<\/p>\n
\u201cThe boundary between a sigma bond and a pi bond is now sort of smeared,\u201d Wang said. \u201cWe still have three bonds, but we don’t really strictly have a sigma or a pi anymore.\u201d<\/p>\n
To show evidence for this bonding hybridization, Wang and his team, led by Brown Ph.D. students Deniz Kahraman and Jie Hui, formed molecules made from bismuth and carbon. Bismuth is a heavy element \u2014 right next to lead on the periodic table \u2014 where relativistic effects should be important. After cooling the molecules to near absolute zero, the team analyzed them using photoelectron spectroscopy. The technique uses a laser to knock individual electrons out of their positions in the molecule. The distance each electron flies tells the researchers how strongly they were bound.\u00a0<\/p>\n
The photoelectron spectrum showed that the carbon-bismuth bonds did not fit the traditional triple-bond picture of one sigma and two pi bonds. Instead, the structure looks more like one pi bond and two hybrid sigma-pi bonds.\u00a0<\/p>\n
Wang says the experimental verification of the relativistic structure may spur a rewriting of chemistry textbooks, especially as heavy elements \u2014 bismuth in particular \u2014 garner more research interest. Bismuth could be an alternative to toxic lead in next-generation solar cells. It has also drawn interest in research related to quantum materials and quantum computing.\u00a0<\/p>\n
\u201cMaybe this will become the new textbook idea as we are dealing with more and more heavy chemistry of the heavy elements,\u201d Wang said.\u00a0<\/p>\n
The work was funded by the U.S. National Science Foundation (CHE-2403841) and the U.S. Department of Energy (DE-SC0008501).<\/p>\n","protected":false},"excerpt":{"rendered":"PROVIDENCE, R.I. [Brown University] \u2014 Brown University chemists have provided direct evidence that upends the textbook explanation of…\n","protected":false},"author":2,"featured_media":536135,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[24],"tags":[85,46,370,141],"class_list":["post-536134","post","type-post","status-publish","format-standard","has-post-thumbnail","category-physics","tag-il","tag-israel","tag-physics","tag-science"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts\/536134","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/comments?post=536134"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts\/536134\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/media\/536135"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/media?parent=536134"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/categories?post=536134"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/tags?post=536134"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}