| Homology (chemistry) ： ウィキペディア英語版|
In chemistry, homology refers to the appearance of homologues. A homologue (also spelled as homolog) is a compound belonging to a series of compounds differing from each other by a repeating unit, such as a methylene bridge −−, a peptide residue, etc.〔(Glossary of Terms Used in Medicinal Chemistry ) (IUPAC Recommendations 1998)〕
A homolog is a special case of an analog. Examples are alkanes and compounds with alkyl side chains of different length (the repeating unit being a methylene group -CH2-).
On the periodic table, homologous elements share many electrochemical properties and appear in the same group (column) of the table. For example, all noble gases are colorless, monatomic gases with very low reactivity. These similarities are due to similar structure in their outer shells of valence electrons. Mendeleev used the prefix eka- for an unknown element below a known one in the same group.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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