valence bond theory- orbital hybridization-Sp2 hybridized orbitals in graphite

if you wanted to melt diamond (tetrahedral carbon) what would have to happen?

“melt” meaning bc of :

• really high temp

• lots of energy

why do metals melt and diamonds do not?

diamonds have a unique crystal structure with incredibly strong covalent bonds between carbon atoms, requiring a significantly higher amount of energy to break and melt, while metals have weaker metallic bonds that are easier to disrupt with heat; essentially, diamonds need much more extreme temperatures to melt compared to most metals. 

what are the 2 models of bonding?

molecular orbital & valence bond

molecular orbital model of bonding:

• atomic orbitals combine to form an equal number of molecular orbitals

• each orbital can contain up to 2 electrons

• electrons in bonding orbitals stabilize the system

• electrons in anti bonding orbital make it less stable

• electrons are delocalized(not at anyone place)

• no hybridization

valence bond model of bonding:

• atomic orbitals overlap to form a bond

• greater the overlap, stronger the bond

• each bond made up of 2 electrons

• electrons are localized in the bond

• hybridization=specific shapes

how can carbon form 4 identical bonds in diamond?

• uses hybrid orbitals

# atomic orbitals in =

# of hybrid orbitals out

how many atomic orbitals (on one carbon) should combine to make 4 hybrid orbitals?

• 4

bonding in diamond(valence bond model):

• atomic orbitals “hybridize” (mix up) to form bonding orbitals that then combine with orbitals from other atom to form a bond

1s-orbital+3 p orbitals = 4 sp3 orbitals→ tetrahedral geometry

to form 4 bonds:

carbon hybridizes the 4 orbitals that are used for bonding

since one s and 3 p orbitals combine

call them sp3 orbitals

bonding in diamond shape:

natural shape comes from 2 items that want to be repeling from each other is going off in 4 different directions thats where the tetrahedral shape comes from

(bonding in diamond ) when the hybrid orbitals combine there is a large gap bw the bonding +

anti bonding molecular orbitals(rlly important) > combo of 2 bonding theories

bonding in tetrahedral C:

• hybridized atomic orbitals(sp3) give rise to strong directed bonds

  • these bonds give rise to high MP/decompositon temp. - bc these bonds have to be broken to melt diamond(in fact diamond decomposes rather than melts)

  • these bonds are “sigma bonds”

end to end overlap=

sigma bonds

sigma bonds link to MO theory:

end to end bonding (overlap) of orbitals

sigma orbital formation from

2 p orbitals

sigma orbital formation from

2 sp3 orbitals

diamond properties explained:

• hard

  • 3d network(stationary bonds) of strong bonds, you would have to break bonds to disrupt a crystal

• high MP

• doesnt conduct electricity

  • electrons are located in bonds bw atoms-not free to roam(e^- locked in place)

  • there is a large “bond gap” bw the bonding and anti bonding orbitals

• translucent

  • light passes through or is reflected to absorb light on electron must be promoted to high energy level since there is a large “bond gap” bw the bonding and anti bonding orbitals

bonding in graphite:

• one s and 2 p orbitals hybridize to give 3 sp2 orbitals (there is a p orbital left over)

  • s pp → sp2

  • 1 s orbital +3 p orbitals → 3 sp2 orbitals+ 1 unchanged p orbital

• geometry is trigonal plane

• C-C-C bond angle is 120 degrees

• when the sp2 hybrid orbitals combine they form sigma bonding molecular orbitals

• the leftover p orbitals (one on each carbon) combine side to side to form a large number of molecular orbitals(pie bonding)

double bonds:

• carbon can mix the s and any number of p orbitals- leaves one p orbital open

  • here C has mixed the s and 2p’s=sp2

  • geometry:trigonal planer

  • 3 sigma bond- and one pi bond bw the C and the O

    • first bond is always a sigma(cylindrical - di

triple bond:

• carbon can mix its S and one p orbital to make sp hybridization

  • one sigma,2 pi bonds=triple bond

  • linear geometry

• pi bonds-combination of py and pz orbitals

  • pi orbital formation from 2 p orbitals

  • formation of sigma and pi molecular orbitals from 2 sp2 hybridized

graphite:

• has a “localized” sigma bond framework (explained by overlap of hybridized orbitals)

• has a “delocalized” pi network over the whole sheet of atoms(explained by delocalized pi molecular orbitals)

  sigma= stationary

graphite properties explained:

• graphite conducts electricity bc it has delocalized pi MO’s over the whole structure (jus like metal bonding)

• shiny-bc it can absorb and emit photons(jus like metals) → a lot more blended MO

• slippery-sheets can slide over each other-only “held together” by LDFs (sheets are large so LDFs add up to be pretty strong) (like metal bonding)

diamond:

• C-C

• Sp3

• strong o- bond

graphite:

• -c=C<

• sp2

• strong o- bond

• pi bond