ATOMIC ORBITAL

[ttuankiet2005]

hello everybody. my name is kiet . I have some problems about atomic orbital .In CH4, cacbon have to be excited . Why does the cacbon be excited?Can u tell me about it?

[Houston]

Have you learned much about atomic orbitals? and hyrbidization too?

Basically for Carbon:

___ ___ ___
2px 2py 2pz

__
2s

__
1s

Now, generally, the 1s will have 2 electrons in it (one spin up, one spin down). The 2s will also have 2 electrons, 1 spin up, one spin down.
since Carbon has 6 electrons, the remaining two will go into the 2p orbitals (for this case, we'll just say one goes into 2px spin up, and one goes into 2py spin up. According to all principles (Hund, Schrodinger, Pauli Exclusion etc). As you can see, Carbon will only have 2 unpaired electrons and thus can only attach to 2 other atoms right? Well, if you excite the carbon, the one of the 2s orbitals will be promoted and be in the 2pz, spin up. you now have 4 orbitals with only 1 electron each (eerily convenient, since it bonds to 4 hydrogen atoms, which also have 1 electron each). So there you have it. , you need to excite the electron to have 4 orbitals of one electron each,

Note that this alone is slightly wrong, since you would not have a tetrahedral atom, since the s orbitals are spherical, and p orbitals are dumbell shaped and at angles of 90 degrees to one another. to get the right geometry, the s and the 3 2p orbitals then combine to create 4 new orbitals which point to the 4 corners of a box, creating a tetrahedral shape. from this you have the right geometry and the right number of possible bonds.

[ttuankiet2005]

You say right.But I don t know why the cacbon is excited.My friend say that "cacbon is excited by the Hydro".My other friend say that "we have provide energy about 1500 Centigrate for C and H to create CH4 following to the reaction C+H_CH4 ,so the C will be excited .Then the C will hybridize sp3."Im very embarrassed.I agree with the first opinion.And you?How do you think ?Im very happy when you reply.

[Houston]

There are generally two ways any molecule or atom is excited. It either is given heat (by you), or it gets hit with ultraviolet (UV) light (from the sun). In most cases, this is enough to promote the electron to the higher orbital. I am not sure that the hydrogen atom can just excite the electron to jump up to the 2p orbital, I would be inclined to say that it is because of heat or ultraiolet light.