Allred-Rochow scale
From Free net encyclopedia
The Allred-Rochow scale in chemistry is a measure of electronegativity.
The electrostatic force of attraction between an electron and the nucleus is given by:
- e²Z/r²
where r is the distance between the electron and the nucleus (covalent radius). e is the charge on an electron. eZ is the charge effective at the electron due to the nucleus and its surrounding electrons.
The quantity Z/r² correlates well with Pauling electronegativities and the two scales can be made to coincide by expressing the Allred-Rochow electronegativity as:
- AR=0.744 + 0.359Z/r²
This Electronegativity is often specified as χAR.
As a general rule, the electronegativity increases as one goes across (to the right) and up the Periodic Table.
Alternative scales are called the Mulliken scale and the Pauling scale.
Further Information:
WebElements - Useful definition http://www.webelements.com/webelements/properties/text/definitions/electroneg-allred.html