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The common atom that connects the two (or sometimes three) rings is called the spiro atom. [2]: SP-0 In carbocyclic spiro compounds like spiro[5.5]undecane, the spiro-atom is a quaternary carbon , and as the -ane ending implies, these are the types of molecules to which the name spirane was first applied (though it is now used general of all ...
A chemical element, often simply called an element, is a type of atom which has a specific number of protons in its atomic nucleus (i.e., a specific atomic number, or Z). [ 1 ] The definitive visualisation of all 118 elements is the periodic table of the elements , whose history along the principles of the periodic law was one of the founding ...
Nonterminal symbols are those symbols that can be replaced. They may also be called simply syntactic variables. A formal grammar includes a start symbol, a designated member of the set of nonterminals from which all the strings in the language may be derived by successive applications of the production rules.
Elemental phosphorus was first isolated from human urine, and bone ash was an important early phosphate source. Phosphate mines contain fossils because phosphate is present in the fossilized deposits of animal remains and excreta. Low phosphate levels are an important limit to growth in a number of plant ecosystems.
It can also be used with highly specific meanings in specialised contexts. In the description of protein structure, in particular in the Protein Data Bank file format, a heteroatom record (HETATM) describes an atom as belonging to a small molecule cofactor rather than being part of a biopolymer chain.
An atom (or ion) whose oxidation number increases in a redox reaction is said to be oxidized (and is called a reducing agent). It is accomplished by loss of one or more electrons. The atom whose oxidation number decreases gains (receives) one or more electrons and is said to be reduced. This relation can be remembered by the following mnemonics.
Since 1988, it has been called Group 15 by the IUPAC. Before that, in America it was called Group VA, owing to a text by H. C. Deming and the Sargent-Welch Scientific Company, while in Europe it was called Group VB, which the IUPAC had recommended in 1970. [2] (Pronounced "group five A" and "group five B"; "V" is the Roman numeral 5).
The practice also continues with tritium compounds. When the name of the solvent is given, a lowercase d is sometimes used. For example, d 6-benzene or C 6 D 6 can be used instead of C 6 [2 H 6]. [14] The symbols for isotopes of elements other than hydrogen and radon are no longer used in the scientific community.