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Author: Subject: Why do electrons have more kinetic energy when closer to the nucleus?
dolimitless
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[*] posted on 7-6-2009 at 02:10
Why do electrons have more kinetic energy when closer to the nucleus?


Also similarly, why do electrons have less potential energy when closer to the nucleus?

Please can someone help me and explain in laymen's terms? I don't understand it. I know when electrons are seperated by large distances, they are less likely to interact with the positive charge of the protons of the nucleus. Is that why there is less "potential" energy?

So, there is more kinetic energy (energy due to motion) when electrons are closer to the nucleus, because the electrostatic attraction is greater?
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dolimitless
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[*] posted on 7-6-2009 at 02:11
How is ionization an endothermic reaction?


I don't get how ionization is an endothermic reaction.

In an endothermic Reactions: the reactants have less potential energy than do the products. Energy must be input in order to raise the particles up to the higher energy level.

The ionization energy, is the energy required to completely remove a valence electron from a gaseous atom or ion.

EX: Na(g) → Na+(g) + e- I1 = 496 kJ/mole

The reactant though, Na, has more potential energy (it is further away from the nucleus when compared to its ionic counterpart, which just lost an electron) than the product?

Am I thinking wrong?
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dolimitless
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[*] posted on 7-6-2009 at 02:12
What is meant by a gaseous atom in ionization energy?


The ionization energy is the energy required to completely remove a valence electron from a gaseous atom or ion.

What is meant by a "gaseous" ion? Does that simply mean an atom in its ground state?
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Hydragyrum
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[*] posted on 7-6-2009 at 05:08


A gaseous atom (or ion, or molecule) is one which is suspended either in vacuum or in a gas (that is, it is not dissolved in a liquid, nor is it contained in a solid).

What it is referring to here is that no other chemical species are close enough to influence the ionisation potential of the electron (which therefore means that the value measured is intrinsic to that atom or ion and nothing else).




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Hydragyrum
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[*] posted on 7-6-2009 at 05:31


Hmm, tried to write this once already, so this time it's shorter - sorry!

For reaction Na(g) → Na+(g) + e-

This is endothermic because removing a negative electron from a neutral atom to give a positive ion requires work - in the gaseous state, neutral atoms are always more stable than the ionised pair of cation plus electron. This is simply the law of charge attraction, which extends out to infinite distance.

When you say, "The reactant though, Na, has more potential energy (it is further away from the nucleus when compared to its ionic counterpart, which just lost an electron) than the product?" you are mistaken because the electron you have ionised is now much further away from the nucleus than it was prior to ionisation. Does this make sense?




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[*] posted on 7-6-2009 at 05:48


You ask, 1. "Why do electrons have more kinetic energy when closer to the nucleus?", and 2. "Why do electrons have less potential energy when closer to the nucleus?"

These questions are really asking the same thing from different points of view. Easiest to explain in terms of gravity - if you throw a ball upwards, it follows a parabolic arc during which it will reach maximum height before returning to Earth. When you let go it is moving with high speed = high kinetic energy. When it reaches the highest point, it is for an instant at rest (kinetic energy = 0) but has high potential energy (the potential to do work is high because it is far from equilibrium: the equilibrium state is where the ball is on the ground, not motionless in the air). As it falls back to Earth, it loses potential energy but gains kinetic energy as its speed increases.

When it reaches the ground, its kinetic energy is at a maximum, while its potential energy = 0.

So, an electron approaching the nucleus is like the ball approaching the Earth - as it approaches, it speeds up (has more kinetic energy) while the potential energy is at a maximum at infinite distance, and decreases towards zero as it approaches the nucleus.

Your last line is correct - the greater electrical attraction at shorter distances give the electron greater kinetic energy. Potential energy is just that: it is the potential to do work - this is a slippery concept, perhaps someone else can explain it better than I can.




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[*] posted on 7-6-2009 at 06:01


These sound remarkably like homework questions, to me. You started three threads to ask pedagogical questions that belong if anywhere in the Short Questions thread.

Don't ask others to do your class assignments, fella. It is rude and no way to learn.

[Edited on 7-6-2009 by Sauron]




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[*] posted on 7-6-2009 at 07:51


Congratulations Dolimitless! To my knowledge you are the first member who managed to open three threads on the same topic in the same section in the timespan of 2 minutes.
Crossposting is not tolerated here as it brings confusion to the forum. Also, open homework related topics only in the Beginnings section where I'm moving this anyway.
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dolimitless
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[*] posted on 7-6-2009 at 10:47


NONE OF THESE WERE HOMEWORK QUESTIONS

They were simply questions I am asking because I am trying to self-teach myself chemistry during this summer as I am taking it in the fall. Since my knowledge of chemistry is limited, I did not know the answer to the questions in the frame of mind / context I was thinking.

Thank you for those who replied, and for those who were rude....well you were wrong. Sorry for trying to have an intriguing mind.

If anyone else can post anymore insight/input to my questions, I would really appreciate it. Thanks for taking the time to answer my questions! This forum is great!
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[*] posted on 7-6-2009 at 10:52


Quote: Originally posted by Sauron  
These sound remarkably like homework questions, to me. You started three threads to ask pedagogical questions that belong if anywhere in the Short Questions thread.

Don't ask others to do your class assignments, fella. It is rude and no way to learn.

[Edited on 7-6-2009 by Sauron]


I tried answering the questions myself and gave my own viewpoint and what I thought was the proper explanation, I don't see what's the problem. And they were not HW questions. :mad:
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[*] posted on 8-6-2009 at 11:16


Electrons are charged particles and when they move EM radiation is given off. This includes spin. The example using a ball thrown in a parabolic path where the vertical vector equals zero ( P.E. max, K.E. zero) at the apex is not accurate. That is classical mechanics and electrons follow quantum mechanics. It has been a long time since my P Chem class so I won't try to explain. The information is out in the net. For example, http://www.chem1.com/acad/webtut/atomic/WhyTheElectron.html
Some of these places have nice graphics and animation. I applaud you on your quest to prepare for your chemistry classes ahead of time. It will give you an edge. I guess some on this forum forget how they felt the summer before they took chem.
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