Wednesday, January 25, 2012

Do specific elements have specific numbers of shells for their electrons?

If yes how come an electron can jump from one shell to the other (flame tests)? And can you please illustrate or at least describe how these things work, because it really confuses me...

Do specific elements have specific numbers of shells for their electrons?
The electrons are found in specific shells, yes.



The flame takes electrons from occupied orbitals into unoccupied orbitals (meaning that they don't disturb those other electrons in the "assigned" shells. When the excited electron relaxes back to it's original shell, it emits the photon that you see.



Hope this helps
Reply:This can be rather tough to explain in a few sentences. If you be a lot easier if you have learnt some quantum physics, or something related to light spectroscopy.



There are many discrete energy levels an electron could stay in. When energy is provided, and it matches the difference between 2 different states, there is a possibility for the atom/molecule to become excited, provided that the transition is allowed.



Here is a link to some basic terms:

http://www.astronomy.ohio-state.edu/~pog...
Reply:It's easy. Atoms have energy level groups, or shells, that their electrons fall into. They start by filling up the first shell, when it's full they start filling up the next shell, etc (in very heavy elements, however, sometimes a few electrons will go in a higher shell before filling up the last one. I don't know why that is but it's the exception to the rule). The valence numbers are always the same. The first shell is 2, the second is 8, the third is 18, then I don't remember after that, but they keep getting bigger.



Take for example Lithium. It has 3 protons %26amp; 3 electrons. The first 2 electrons are in the first shell and the third electron is in the second shell. The third electron has more energy than than the first two.



Take for example oxygen. It has 8+ and 8-, so the first shell is full and the second has 6- so it needs 2 to be full. This is where covalent bonding comes into place. Two oxygen atoms will share 2 electrons w/ eachother so both of their outer shells are full.



Now if you start putting energy into an atom, once it gets enough energy, one of the electrons will jump up to a higher energy level (shell). But obviously it is unstable in this state, and so it doesn't stay there for long. It jumps back down to its natural energy level, and releases that extra energy in the form of a photon.



That is how astronomers can look into space and figure out what element they are seeing. Because for each element it takes a specific amount of energy to cause that electron to jump to a higher energy level (by the way this is called a "quantum leap") and when it falls back down it releases that exact amount of energy so it emits a photon at a specific wavelength. Scientists know the wavelength for many elements that is how they can tell what stuff out in space is composed of.


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