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Phi (/ f aɪ /; [1] uppercase Φ, lowercase φ or ϕ; Ancient Greek: ϕεῖ pheî; Modern Greek: φι fi) is the twenty-first letter of the Greek alphabet. In Archaic and Classical Greek (c. 9th to 4th century BC), it represented an aspirated voiceless bilabial plosive ( [pʰ] ), which was the origin of its usual romanization as ph .
The OpenType font format has the feature tag "mgrk" ("Mathematical Greek") to identify a glyph as representing a Greek letter to be used in mathematical (as opposed to Greek language) contexts. The table below shows a comparison of Greek letters rendered in TeX and HTML. The font used in the TeX rendering is an italic style.
The Greek letter φ in their name refers to f orbitals, since the orbital symmetry of the φ bond is the same as that of the usual (6-lobed) type of f orbital when seen down the bond axis. There was one possible candidate known in 2005 of a molecule with phi bonding (a U−U bond, in the molecule U 2 ). [ 1 ]
The Greek alphabet has been used to write the Greek language since the late 9th or early 8th century BC. [2] [3] It was derived from the earlier Phoenician alphabet, [4] and is the earliest known alphabetic script to have developed distinct letters for vowels as well as consonants. [5]
This is a list of letters of the Greek alphabet. The definition of a Greek letter for this list is a character encoded in the Unicode standard that a has script property of "Greek" and the general category of "Letter". An overview of the distribution of Greek letters is given in Greek script in Unicode.
Chemical symbols are the abbreviations used in chemistry, mainly for chemical elements; but also for functional groups, chemical compounds, and other entities. Element symbols for chemical elements, also known as atomic symbols , normally consist of one or two letters from the Latin alphabet and are written with the first letter capitalised.
Euclid's Elements (c. 300 BC) provides several propositions and their proofs employing the golden ratio, [15] [c] and contains its first known definition which proceeds as follows: [16] A straight line is said to have been cut in extreme and mean ratio when, as the whole line is to the greater segment, so is the greater to the lesser. [17] [d]
Although notation was partly standardized, style and symbol varied between alchemists. Lüdy-Tenger [1] published an inventory of 3,695 symbols and variants, and that was not exhaustive, omitting for example many of the symbols used by Isaac Newton. This page therefore lists only the most common symbols.