How to calculate polarity basic, i know

[professor]

i cannot get this i have read through texts, and have made probably incorrect postulates of my own on the matter but canot find an easy, or a way at all to calculate spin. (my postulates are limited to the idea that one or two free electron pairs on a simple molecule with one center aom causes polarity, unless the center atom is a noble gass.) even that basic idea i have made myself seems to well... not work all the time (or atleast i wouldent expect it too...does anyone know how i can accurately predict polarity

 

[marlon]

Are you sure you are not talking about polarization and Electric dipoles . Jus click the 'polarization of dielectrics'-balloon

marlon

 

[professor]

i looked over your recomendenation, and found the site very usefull in general as i have used it before, though this is not what i think i am looking for... i have questiones ask me things such as (simple ex.) -you have the molocule H(subscript-2)O -would this molocule be polar...i know the watermolocule is polar, but not why. seems like i had it for a while, but i put down the work a day ago and forgot.

 

[marlon]

-you have the molocule H(subscript-2)O -would this molocule be polar...i know the watermolocule is polar, but not why. seems like i had it for a while, but i put down the work a day ago and forgot.

Well, actually that has to do with dipoles and electronegativity (ie the tendency of an atom to attract electrons). O has bigger electronegativity and will attract the unshared electrons of the two H molecules, which leads to small displacement of the unshared electrons. This results in a non uniform charge distribution which leads to the electric dipole. The O atom acquires the negative part and the H atom gets the positive part, that arises due to the unshared electron displacement.

Look at http://www.biology.arizona.edu/biochemistry/tutorials/chemistry/page3.html


you can find the electronegativity of an atom on the Periodic Table
http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/bondd.html

marlon

 

[professor]

yes that's it! i have it again thanks... electron affinity an electronegitivity are the same thing... right?

 

[marlon]

yes that's it! i have it again thanks... electron affinity an electronegitivity are the same thing... right?

NO

electron affinity is the energy necessary to release an electron from the valence band to the vacuul level. Or in other words, the energy necessary to rip off a valence electron from an atom. Thus, the other way around, it is also the energy for an atom to 'swallow' an free electron and become negatively charged ion.

In the electronegativity case, the electron is not swallowed by the atom, it is just attracted towards the atom. THAT IS THE DIFFERENCE

marlon

 

[GCT]

How do you intend to predict polarity when you can't even distinguish electron affinity from electronegativity? Methods of "predicting" polarity are outlined explicitly in a standard chemistry text, and it is one of the easiest things you will learn in general chemistry. If your current chemistry text is inadequate I would suggest Principles of Chemistry by Raymond Chang, any of the last three editions.

the first electron affinity pertains to the reverse process of ionization (the "pulling off" of electrons as marlon has mentioned), a particular electron affinity will be negative of the value of the ionization energy for the corresponding electron. The concept of electronegativity is not as concrete, its specific to the situation btw two different atoms; the ability of a particular atom to "hoard" the electrons relative to another.

 

[professor]

yeah opps about that...i still do have it though I just thought as a side comment that i reminded myself to read about electron affinity then for somereason related it to this...