Lecture Eight Flashcards
What is valance bond theory?
Describes pairs of electrons as either localised in bonds between two atoms (covalent bonds) or localised on a single atom (lone pairs). provides another way to consider the nature of bonding within molecules. A covalent bond forms when the orbitals of two atoms over lap and are occupied by a pair of electrons that have the highest probability of being located between the nuclei.
The localised bonding model deelips orbitals of two types.
One type is a bonding orbital that has a high electron density between two atoms (covalent bonds).
The other type is an orbital located on a single atom (lone pairs). In other words, any electron is restricted to the region around a single atom, either in a bond to another atom or in a non bonding orbital.
What are the characteristics of hybid orbitals?
A set of overlapping orbitals has a maximum of two electrons that must have opposite spins.
The greater the orbital overlap, the stronger (mroe stable) the bond.
Hybridization = mixing of certain combinations of atomic orbitals to generate new hybrid atomic orbitals.
The hybrid orbitals have particular shapes that a suited to various molecular geometries.
Five hybridizaion schemes exist: sp, sp2, sp3, sp3d and sp3d2.
First three are the most common.
Each of these may be considered a mathematical combination of the atomic orbitals which were used to construct them.
What are the characteristics of the sp hybrid orbital?
By mathematically combining the Px and s atomic orbitals, in phase and out of phase conbinations lead to two bybrid orbitals.
Note that the energy of the two hybrid orbitals is an average of the energ of the two atomic orbitals used. Also note that the energy fo the Py, and Pz atomic orbitals remain unchanged.
What are the characteristics of the SP2 hybird orbitals?
Arise from mixing three atmoic orbitals.
Combinging the Px, Py and S atomic orbitals generates three, 3-fold SP2 hybrid orbitals.
Note that the energy of the three hybrid orbitals is an average of the energy of the three atomic orbitals used.
Also note that the energy of the Pz atomic orbital remains unchanged.
What are the characteristics of the SP3 hybrid orbitals?
SP3 hybridisation arises from teh mixing of four atomic orbitals.
Combinging the Px, Py, Pz and S atomic orbitals generates these four orbitals.
Again, note how the energy of the four hybrid orbtals is an average of the energy of the four atomic orbitals used.
No hybridised s or p atomic orbitals remain.
What are the gemoetric shapes of the hybridised molecules?
The number of hybrid orbitals obtained always equals the number of atomic orbitals mixed.
The type of hybrid orbitals varies with the types of atomic orbitals mixed.
How can pi bonds form in valance bond hybridization?
The unhybridised atomic orbitals can participate in pi bonding with neighbouring atoms.
One pi bond forms when there are two regions of electron density.
What are the four steps to finding the appearance of hybridized atoms.
Draw the lewis structure.
Determine the shape using VSEPR.
Specify hybrid orbitals involved in sigma bonding.
Extra points of sharing electrons from pi bonds.
