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Moving, electron shells? 
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#1
Apr2108, 11:10 PM

P: 11

1. The problem statement, all variables and given/known data
Recently in my chemistry class my teacher told us that, the greater the atomic number the smaller the radius of the electron. Because there is more protons pulling on electrons. which would mean the elctrons move inwards. This doesnt seem quite right to me as i thought that the distance of electron shells are constant for all atoms, but i cant find any disproofs or paradoxis with this statment so, am I wrong? 2. Relevant equations none, however an electron shell diagram could be usefull 3. The attempt at a solution i was thinking that if electron shells could move then, theoreticly the atom could collapse by the electrons flying into the nucleus. However this doesnt seem to help me or make sense. 


#2
Apr2108, 11:24 PM

P: 45

Also, every atomic element will have a minimum energy level for it's electrons, but that does not mean that the minimum energy for Hydrogen will be the same for, say, Gold or Lead. 


#3
Apr2208, 02:50 AM

HW Helper
P: 2,249

Hi gateman234,
The size of the atoms decreases as you move along a single row in the periodic chart. So for the atoms in the third row, with n=3, sodium has the largest radius. Then as Z increases (but the extra electrons keep going into the n=3 shell), the radius decreases until argon has the smallest size. But when you go to the next row, potassium, with an electron in the n=4 shell, is larger than all of the elements in the previous row. (At higher Z values, the progression isn't quite so regular, but the overall trend still holds.) 


#4
Apr2408, 01:08 AM

P: 11

Moving, electron shells?
thanks for this,
but i still dont really get it because wouldnt Na would have energy levels 1,2 complete with one electron in the third shell (3s). while Cl would have 1,2 (3s) energy levels complete with one electron missing from (3p). so Cl would have a bigger radius? unless the energy levels distance from the nucleus changes dependant on the amount of protons. also wouoldnt alot of elements in between Na and Cl have the same radius? i must be missing something, help 


#5
Apr2408, 01:20 AM

HW Helper
P: 2,249

For the particular case you mentioned, Cl is quite a bit smaller than Na. 


#6
Apr2408, 02:29 AM

P: 45

the whole point of classifying subshells as for example, s or p, is because the geometric arrangement is different. S are basically spherical, wheras p are dumbbell shaped. Hence, an s electron can be on average the same distance from the nucleus as a p electron. Just because an electron is in a p orbital does NOT mean that it must be further away. As effective positive nuclear charge increases (i.e. you move along a group), ALL the electrons are "pulled" further in hence decreasing the atomic radius



#7
Apr2408, 05:11 AM

P: 11

ok?,
what about Bores model? because doesnt the different geometric arrangments (s,p,d,f) fill in that order? also, because there are more protons there are also more electrons. so there isnt any exess charge. however if we were talking about ions, it would be different. i think? 


#8
Apr2408, 09:28 AM

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P: 2,249

Start with hydrogen with a specific radius. Then go to helium. Each electron "sees" a nuclear charge of +2 and is pulled in closer to the nucleus. Lithium: each of the n=1 electrons "sees" a charge of +3 and is pulled even closer to the nucleus. For the third electron in the n=2 orbital, it experiences a nuclear charge of +3 but the screening due to the inner electrons create an effective central charge of +1 and so, based on this model, we would expect the third electron to be roughly at the location of the n=1 shell for hydrogen. (However, the reasoning here is just the reasoning in Bohr's model; in real atoms the electrons all interact even within a shell, and so this simple model does not give good numerical results.) 


#9
Apr2508, 02:23 PM

P: 45




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