Fluorine element

موضوع: Fluorine element الأربعاء 25 فبراير 2009, 9:28 am

Brief description: fluorine is a Group 17 element. Fluorine is the most electronegative and reactive of all elements. It is a pale yellow, corrosive gas, which reacts with practically all organic and inorganic substances. Finely divided metals, glass, ceramics, carbon, and even water burn in fluorine with a bright flame. It is not uncommon to see fluorine spelled incorrectly as flourine.

Name: Fluorine
Symbol: F
Atomic number: 9
Atomic weight: 18.9984032 (5)
Standard state: gas at 298 K
CAS Registry ID: 7782-41-4
Group in periodic table: 17
Group name: Halogen
Period in periodic table: 2
Block in periodic table: p-block
Colour: pale yellow
Classification: Non-metallic

Until World War 2, there was no commercial production of elemental fluorine. Atom bomb projects and nuclear energy applications made it necessary to produce large quantities of fluorine since isotopes of uranium can be separated through the gas diffusion of UF6. Reasonably safe handling techniques for fluorine are now available and one can transport liquid fluorine by the ton. Compounds of fluorine with noble gases such as xenon, radon, and krypton are known. Elemental fluorine and the fluoride ion (in quantity) are highly toxic.

Isolation: it would never be necessary to make fluorine gas in most laboratories. Fluorine is available commercially in cylinders but is very difficult to handle. Fluorine may be recovered with difficulty as a highly reactive and corrosive pale yellow gas by electrolysis of hot molten mixtures (1:2) of potassium fluoride (KF) and hydrogen fluoride (HF). The electrolyte is corrosive, so is the product. Grease must be avoided because of the fire hazard. It is difficult to store as it reacts with most materials but steel and Monel metal containers may be used as the metal surfaces deactivate through the formation of unreactive surface fluorides.

The most used definition of electronegativity is that an element's electronegativity is the power of an atom when in a molecule to attract electron density to itself. The electronegativity depends upon a number of factors and in particuler as the other atoms in the molecule. The first scale of electronegativity was developed by Linus Pauling and on his scale fluorine has a value of 3.98 on a scale running from from about 0.7 (an estimate for francium) to 2.20 (for hydrogen) to 3.98 (fluorine). Electronegativity has no units but "Pauling units" are often used when indicating values mapped on to the Pauling scale. On the interactive plot below you may find the "Ball chart" and "Shaded table" styles most useful.

Table of Different types of electronegativity for fluorine. Use the links in the "Electronegativity" column for definitions, literature sources, and visual representations in many different styles (one of which is shown below). All values are quoted on the Pauling scale. Electronegativity Value in Pauling units
Pauling electronegativity 3.98
Sanderson electronegativity 4.00
Allred Rochow electronegativity 4.10
Mulliken-Jaffe electronegativity 3.91 (14.3% s orbital)
Allen electronegativity 4.193

There are a number of ways to produce a set of numbers representing electronegativity and five are given in the table above. The Pauling scale is perhaps the most famous and suffices for many purposes.

Melting point: 53.53 [or -219.62 °C (-363.32 °F)] K
Boiling point: 85.03 [or -188.12 °C (-306.62 °F)] K (liquid range: 31.5 K
Critical temperature: 144 [or -129 °C (-200 °F)] K

One measure of size is the element-element distance within the element. The bond length in FF is: 141.8 pm. It is not always easy to make sensible comparisons between the elements however as some bonds are quite short because of multiple bonding (for instance the O=O distance in O2 is short because of the the double bond connecting the two atoms.

There are several other ways ways to define radius for atoms and ions. Follow the appropriate hyperlinks for literature references and definitions of each type of radius. All values of radii are given in picometres (pm). Conversion factors are:

1 pm = 1 x 10-12 metre (meter)
100 pm = 1 Ångstrom
1000 pm = 1 nanometre (nm, nanometer)
Neutral radii
The size of neutral atoms depends upon the way in which the measurement is made and the environment. Follow the appropriate hyperlinks for definitions of each radius type. The term "atomic radius" is not particularly helpful although its use is widespread. The problem is its meaning, which is clearly very different in different sources and books. Two values are given here, one is based upon calculations and the other upon observation - follow the appropriate link for further details.

Atomic radius (empirical): 50 pm
Atomic radius (calculated): 42 pm
Covalent radius (2008 values): 57 pm
Covalent radius (empirical): 71 pm
van der Waals radius: 147 pm

The following are calculated values of valence shell orbital radii, Rmax

Table: valence shell orbital radii for fluorine. Orbital Radius [/pm] Radius [/AU]
s orbital 40.6 0.766984
p orbital 38.1 0.720013
d orbital no data no data
f orbital no data no data

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موضوع: رد: Fluorine element الخميس 26 فبراير 2009, 12:53 am

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