MadSci Network: Chemistry
Query:

Re: What is meant when a person refers to positive and negative energy ?

Date: Mon Jan 8 19:31:13 2001
Posted By: Paul Henderson, Undergraduate, Small Physics, Fortismere
Area of science: Chemistry
ID: 978121116.Ch
Message:

Hi Crissy The idea of negative energy is quite simple when you understand it, I remember having to think about it a bit before i got it. A typical example is gravitational potential energy: if you have a ball at a height it has GPE. If you drop it, it gains kinetic energy. The GPE is said to be negative as the energy of the ball (that is actually having an effect ie: KE) is increasing as it looses GPE. I hope that makes some sense to you, try reading a Brief History of Time by Stephen Hawking as he explains this much better. (it really isn’t that hard to read! just kinda weird ;-) Now, shielding: This is the effective attraction between electrons surrounding a nucleus in an atom. For example if we have an nucleus of charge +4 and only 2 electrons around it they are quite ‘unshielded’ (i suppose) as they have a greater effective attraction as there is a 2:1 ratio of +ve to -ve charge. If we have the same nucleus but now 4 electrons, the ratio is 1:1 and so they are more shielded. Now, as the distance of electrons increases the effective attraction decreases and so the electrons closer to the nucleus ‘shield’ the attraction of the nucleus from outer electrons. ie: the 1s^2 shell shields the 3s^2. Again, i hope that makes sense. Somewhere in the MadSci archives there is an explanation of why Mercury is a liquid at room temp. it involves ‘shielding’ and is certainly worth reading.

try this link for more info:< http:// library.thinkquest.org/10429/high/indexh.htm>

keep up the good work n’ all Paul Henderson


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