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Chemical similarity (or molecular similarity) refers to the similarity of chemical elements, molecules or chemical compounds with respect to either structural or functional qualities, i.e. the effect that the chemical compound has on reaction partners in inorganic or biological settings.
Thus, on both descending a period and crossing a group by one element, the changes "cancel" each other out, and elements with similar properties which have similar chemistry are often found – the atomic radius, electronegativity, properties of compounds (and so forth) of the diagonal members are similar.
Examples of symmetrical pseudohalogen compounds (Ps−Ps, where Ps is a pseudohalogen) include cyanogen (CN) 2, thiocyanogen (SCN) 2 and hydrogen peroxide H 2 O 2. Another complex symmetrical pseudohalogen compound is dicobalt octacarbonyl, Co 2 (CO) 8. This substance can be considered as a dimer of the hypothetical cobalt tetracarbonyl, Co(CO) 4.
Mg 2+ Disodium phosphate is a very selective reagent for magnesium ions and, in the presence of ammonium salts and ammonia, forms a white precipitate of ammonium magnesium phosphate. Mg 2+ + NH 3 + Na 2 HPO 4 → (NH 4)MgPO 4 + 2Na + Ca 2+ Ca 2+ forms a white precipitate with ammonium oxalate. Calcium oxalate is insoluble in water, but is ...
Merriam-Webster defines chemotaxonomy as the method of biological classification based on similarities and dissimilarity in the structure of certain compounds among the organisms being classified. Advocates argue that, as proteins are more closely controlled by genes and less subjected to natural selection than the anatomical features , they ...
[16] [17] [18] A molecule may be homonuclear, that is, it consists of atoms of one chemical element, as with two atoms in the oxygen molecule (O 2); or it may be heteronuclear, a chemical compound composed of more than one element, as with water (two hydrogen atoms and one oxygen atom; H 2 O). A molecule is the smallest unit of a substance that ...
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Hydrogen can form compounds with most elements and is present in water and most organic compounds. [2] Helium (He) exists only as a gas except in extreme conditions. [3] It is the second-lightest element and is the second-most abundant in the universe. [4]