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electron energy levels - Chem coach? (1 Viewer)
- Thread starter Farmerism
- Start date
onebytwo
Recession '08
i didnt think electrons were orbiting at equal distances from the nuclues - however, thats a good question, what i cant work out is why with hydrogen, its one proton and one orbiting electron dont just fuse, since they are oppositely charged?Farmerism said:
Electrons exist in specific energy levels according to their energy - higher energy allows higher radius of travel from nucleus.Farmerism said:
Electrons can't exist in regions in between shells because stable standing waves cannot be produced in these circumferences ( an even number of wavelengths) - remember that electrons have a wave and particle nature.
Valence electrons are electrons in the outer shell which can take part in bonding,as opposed to electrons in the inner shells which remain untouched during chemical reactions.
Hope this helps.
If you do Physics, you'll cover this in From Ideas To Implementation. Electrons take on specific energy shells depending on the amount energy that they possess. The lower the energy in the electron, the lower the energy shell.Farmerism said:
If some source of energy such as electromagnetic radiation is given to an atom, some electrons get excited and get promoted to a higher energy shell because those electrons use that energy to jump into the next energy shell. Therefore electrons in the valence shell would possess the highest amount of energy. As a result, valence shells can be transferred in chemical reactions such as ionic bonding because the energy in the reaction is enough to pull the electron away from the attractive forces of the atom's nucleus.
If you do Physics, you'll cover this in From Ideas To Implementation. Electrons take on specific energy shells depending on the amount energy that they possess. The lower the energy in the electron, the lower the energy shell.Farmerism said:
If some source of energy such as electromagnetic radiation is given to an atom, some electrons get excited and get promoted to a higher energy shell because those electrons use that energy to jump into the next energy shell. Therefore electrons in the valence shell would possess the highest amount of energy. As a result, valence shells can be transferred in chemical reactions such as ionic bonding because the energy in the reaction is enough to pull the electron away from the attractive forces of the atom's nucleus.
hm but what gives them the particular energy in the first place?.. because all this time i just thought that it was ..A l said:
because the electron with highest energy, or highest reactivity [the electrons in the valence shell, or valence band or something], was furtherest away from the nucleus [due to weak eelctrostatic attraction between electron and nucleus] making it more reactive or have more energy? since it can be used to bond readily...
but this reasoning isnt true... even though thats what my year 11 teacher, who taught us jack said... and then i hear from the chem coach that all electrons are equidistant from the nucleus...
um and i understand that the electron/s in the valence shell take part in the bonding like what pkc said, but why this particular electron?........is it because its got a higher energy level than the others? but then why does this particular electron or electrons have this higher energy level than all the other 'inner' electrons
and im also assuming that these energy level have nothing to do with the fact that electrons have charge..
what do you mean by fuse.. do you mean annihilate.. because theyre not.. 'corresponding' sub particles.. cuz electrons annihlate with positrons.. and. i dunno what the proton cancels out with..onebytwo said:
and i dunno.. sounds kinda dumb but why didnt everything just cancel eachother out. cuz shoudlnt there have been equal amounts of positrons and electrons at the beginning of time.. or is it because electrons just naturally bonded with protons and neutrons and so couldnt annihilate with the positrons.. and so.. are there any positrons existing now?.. i dunno
Electrons in different shells are at different distances from the nucleus. All electrons are not equidistant from the nucleus.Farmerism said:
The radius of an orbit is given by
r=n2a,
where n= shell number and a=0.0529nm.
The energy the electrons have is the sum of their potential and kinetic energies, with the potential energy increasing as they increase their distance from the nucleus.
The total energy (eV) is given by:
E=-13.6/n2
The main reason outer shell electrons participate in bonding is because the outer shell is the only shell (in non Group 8 elements) not completeley filled, so it's the one that needs to gain or lose electrons.
The electron does not spiral into the nucleus of a hydrogen atom because it has enough speed (kinetic energy in the tangential direction) to avoid it. The same way a satellite will continue to orbit around the earth indefinitely provided it maintains its necessary speed.
funking_you
Member
The chem coach did not state that all electrons are equidistant from the nucleus, this would be incorrect.
What i was explaining was the following:
PICTURING ELECTRONS IN THE ATOM:
Electrons in atoms move very rapidly and randomly around the nucleus. They do not (repeat, not) move in fixed orbits like planets around the sun, but move so that their distance from the nucleus varies greatly: at one INSTANT an electrons may be close to the nucleis, the next instant far away from it. Because electrons are extremely small and because the volume available to them to wander around in is so huge, they are able to move about haphazardly without ever colliding. It is because we have many electrons moving randomly through the volume surrounding the nucleus that we use the term ' electron cloud' to describe it.
This description is trying to get you away from thinking electrons are electrons are fixed in 'orbits' that circle the nucleus as the planets circle the sun, which is what the Bohr model teaches you (and what most teachers reinforce), because this is not the real picture. The above description is trying to illustrate the dynamic motion of electrons, and get you away from the constraints and assumption of the Bohr model.
...
QUANTUM MECHANICAL MODEL OF THE ATOM FOR BEGINNERS
Introduction
A discussion the REAL nature of the atom is difficult since the hsc course only ever discusses the Bohr model of the atom, which is a VERY primitive model of the atom, which does not explain much and does not paint a correct picture of the real atom.
The quantum-mechanical model is our best model of the atom. We believe it is the accurate discription of the an atom.
Without going into quantum mechanics too much, here is just a short discussion of some important things to thing about.
LETS BEGIN THE JOURNEY ...
The quantum-mechanical model of the atom is our best model of the atom. According to this model electrons exist in 'atomic orbitals'. It is very important to keep in mind that an "orbital" in the quantum-mechanical model bears NO resemblance to an "orbit" in the Bohr model.
In the Bohr model the 'orbit' was a path supposedly followed by the electron, whereas the 'orbital' is an actual description of the location of an electron.
(EXTENSION: the 'orbital' is actually a mathematical function with no physical meaning, i.e. wave function, however what we are really discussing is the 'atomic orbitals radial probability distribution' which is a physical quantity)
The "orbital" is specified by three quantum numbers:
- 1.one which is related to the orbitals size (n),
- 2.another to its shape l/I] and
- 3.the third to its orientation in space. (ml)
Below is an simple, introductory explaination of each concept:
1.Most students understand that the quantum number (n) specify energy levels, and that the higher the n value, the greater the energy level.
In quantum mechanics, the lower the energy level, the more time ON AVERAGE the the electrons will spend being closer to the nucleus (a more precise way to say this is 'the higher the energy level, the greater the radial probability of electrons being closer to the nucleus, but this involves a maths description).
In quantum mechanics we talk about 'radial probability distributions', in normal english talk this translates to 'shells'. Hence we sometimes call energy levels 'shells'.
Each energy level can hold a total maximum of 2n2 electrons.
2. The orbital shape, designated by, l/I], is technically refered to as the 'angular momentum quantum number' which is usually means nothin to a hsc student.
Because there is not mention of this concept in hsc.
Simply thou, this 'angular momentum quantum number' is refered to as 'sublevels' or subshells, which designate the orbital shape as one of the following:
s sublevel (l/I]=0) : has a spherical shape (max. 2 electrons)
p sublevel (l/I]=0) : has a dumbell shape (max. 6 electrons)
d sublevel (l/I]=0) : looks like two p sublevels joined together (max. 10 electrons)
f sublevel (l/I]=0) : looks like two d sublevels joined together (max. 14 electrons)
3. This third concept is formally known as he 'magnetic quantum number'. It is an extention of the second concept, and doesnt warrent much discussion here.
But as pointed out, it is concerned with the 'orientation of the subshell'.
For example, an s-subshell has a spherical shape, hence 'orientation' of this subshell is irrelevnt in 3D space.
However, for a p-subshell, which has a dumbell shape (image blowing up two seperate balloons and tie a not in each, then tie them both together at their nots: thats what a p-subshell looks like) This subshell, can be orientated either in the x-axis, y-axis or z-axis, so it has three seperate orientations of the one type of subshell. Each of these orientations are unquie, and the 'magnetic quantum number' actually differentiated between these three.
FINALLY, what IS AN ORBITAL: it is allowed combinated of each of the above three quantum numbers.
Hence for each orbital, you will specify each of the three.
Each orbital can hold a maximum of 2 electrons.
The two electrons in each orbital have 'opposite spins': one has an up-spin, and one has a down spin.
What is this spin? well its NOT like a toy spin top, although many people picture it like that. If you do physics. It is an intrinsic angular momentum. (intrinsic means it is characteristic which is essential and specific to that thing)
Electron spin is quite complex and mathematical, so i wont give you a proper description.But a valid way to introduce this concept is to remember from physics (if you do it!), that a rotating electrically charged body can create a magnetic field, so the electron particles 'spin' essentially creates a magnetic dipole moment; the direction of this magnetic dipole moment is either up or down.
SUMMARY:
Electrons exist in 'atomic orbitals'. Each atomic orbital is defined by and descriped by three quantum numbers:
- [1]principle quantum number: which specifies the energy level (shell), and is will also determine the orbitals size.
- [2]angular momentum quantum number: which defines the sublevels (subshells) that exist. This will specific which of the 4 possible shapes the sublevel has
- [3]magnetic quantum number: this described the orientation on the sublevel (subshell) in 3D space with respect to the 3 cartesion axes.
Each atomic orbital will have 3 different quantum numbers which specify it, and each atomic orbital can hold 2 electrons, which have opposite spin.
Electron spin is designated by a different quantum number, so tecnically EACH ELECTRON is specific by 4 different quantum numbers.
No two electrons will have the same 4 quantum numbers.
...
Furthermore, some asked a question about electrons collapsing, so
ENERGY LEVELS & ELECTRONS COLLAPSING:
Since positive and negative charges attract each other, we might expect the electrons to be attracted to the nucleus, and the atom to collapse into a tiny blob. The fact that this does not happen indicated that the electrons posses energy, sufficient to resist the attraction towards the positive nucleus. We find electrons in an atom exist in discrete energy levels.
FINAL REMARKS
If you have read this far, WELL DONE !!!, if you take anything from the above it should be this:
The Bohr model of the atom is VERY primitive, and actually has many assumption and ideas which are wrong, and many which are misleading.
The Bohr model of the atom is useful to introduce the structure of the atom and electron configurations, to junior science students, and it works well in explaining simple chemical reactions.
It is unfortunate that as senior higher school students 11 & 12 students, you are still feed the Bohr model.
Just remember that the atom is much more complex and beautiful that what you are taught.
At first the quantum mechanical model is torturous to say the least, cause it requires a whole new way of picturing the atom, but with time, everyone can master it and then apply it to chemical reactions.
GOOD LUCK
George J
p.s. students studying quanta to quarks in physics or the chemistry or art as you chemistry option should print off this thread and read it and keep it, if will come in very handy when you study those options.
Any student that will study both options is VERY lucky.
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This would be true if the electron in a hydrogen atom could resist the attraction of the positive nucleus, but it can't and it doesn't.chemcoach said:
The same way a satellite does not resist the force of gravity from earth, it just goes with flow.
In the case of a satellite, the result of this inward travel forced by gravity combined with a movement at 90 deg to the force due to the satellite's speed, is a uniform circular path. Physics student will know what I mean here (Topic "Space"- HSC).
The same applies to the case of an orbiting electron, except the inward force is an electrostatic one rather than a gravitational one, and the tangential speed is from the electron's kinetic energy. There is no resistance necessary to explain the motion.
Basically, in a nutshell, the model of the atom we study in the HSC course (Bohr model) is NOT the actual model scientists use today. This is because the quantum model is very complex and Bohr model is simple enough to explain large numbers of phenomena. In other words, you are getting confused between two different models (proposed in two different time frames of history with one being seen as more accurate than the other) of the atom.
Just stick with the basic Bohr model and everything you need in the course would fit in nicely.
Just stick with the basic Bohr model and everything you need in the course would fit in nicely.