The first three horizontal rows or periods in the modern periodic table consist entirely of representative elements. Formulas for chlorides of the first dozen elements that show the periodic variation of valence Element This agrees with the valence rules derived from the periodic table, and results in formulas for chlorides of the first dozen elements that show the periodic variation of valence. For representative elements the number of valence electrons is the same as the periodic group number, and the number needed to match the next noble-gas configuration is 8 minus the group number. That is, the valences of the representative elements may be predicted on the basis of the number of valence electrons they have, or from the number of electrons that would have to be added in order to attain the same electron configuration as an atom of a noble gas. ![]() Many of the chemical properties of the representative elements can be explained on the basis of Lewis diagrams. Most of the elements whose chemistry and valence we have discussed so far fall into this category. The representative elements are those in which the distinguishing electron enter an s or p subshell. The type of subshell ( s, p, d, f)into which the distinguishing electron is placed is very closely related to the chemical behavior of an element and gives rise to the classification shown by the color-coding on the periodic table seen here. This last electron is called the distinguishing electron because it distinguishes an atom from the one immediately preceding it in the periodic table. ![]() Since it is the outermost (valence) electrons which are primarily involved in chemical interactions between atoms, the last electron added to an atom in the building-up process is of far more interest to a chemist than the first. The commonly used long form of the periodic table is designed to emphasize electron configurations. Only 68% of people with IBD appeared to carry the gene, along with 40% of babies less than 3 months old, who are at a heightened risk for jaundice.\) They also looked for the gene in the guts of more than 1,800 adults with IBD and of about 4,300 healthy infants and found it was much less prevalent. They found that 99.9% of the people had gut bacteria that carried the gene for bilirubin reductase. The team then genetically screened the gut microbiomes of 1,801 healthy adults, hunting for the pee-coloring gene. coli.īy searching for the gene in all gut bacterial species, they discovered that the enzyme is mainly produced by species belonging to a large group known as the Firmicutes, which dominate the human gut microbiome. They then tested whether the enzyme was able to facilitate this conversion in the model organism Escherichia coli, better known as E. In this way, they identified the gene that encodes bilirubin reductase. In the new study, the researchers compared the genomes of species of human gut bacteria that can convert bilirubin into urobilinogen and those that lack this capacity. Previous research into the color of urine was conducted before genomic sequencing technologies became widely available, which made it difficult to identify which strains of bacteria were actually present in urine samples, the authors wrote in the paper. "It's remarkable that an everyday biological phenomenon went unexplained for so long, and our team is excited to be able to explain it," Brantley Hall, the lead study author and an assistant professor in the Department of Cell Biology and Molecular Genetics at the University of Maryland, said in a statement. Jaundice develops because of a build-up of bilirubin in the blood, while people with IBD have been observed to have l ower levels of urobilin than adults without the condition. ![]() Namely, it could improve our understanding of the role of the gut microbiome - the community of microbes in the gut - in conditions such as jaundice, the yellowing of the skin and eyes, or inflammatory bowel disease (IBD), chronic inflammation in the digestive tract. The authors of the new study say that the discovery could have potential health implications.
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