Hybrid Orbitals and Molecular Orbital Theory (Chapter 9)

Nov 10, 12 and 14 Lectures

Use ____ orbitals when you want to form a tetrahedral geometry from a central atom

sp³

to form trigonal planar geometry, hybridize

sp² orbitals

use ___ to form the sigma bond in all linear molecules

sp

the # of orbitals you hybridize for a geometry is related to the # of

sigma bonds

Kekule Structure

Lewis structure but without lone pairs

Condensed Structure

no bonds drawn in the core structure

ex: CH3CH2CH2CH3

Skeletal structures

Hydrogen atoms assumed, carbons represented by vertices

chirality

a property of a molecule that does NOT apply to its mirror image (optical isomerism)

• structures with the same molecular formula can react differently due to their orientations in space 

most common chiral molecule!!

4 different atoms (not hydrogen) attached to carbon

chiral molecules

their mirror images can NOT be superimposed upon themselves

Number of Molecular Orbitals always equals 

the number of Atomic Orbitals used to make the Molecular Orbitals

Bond Order (predicts amt of bonds in a molecule)

Half of the number of (bonding electrons - antibonding electrons)

homonuclear diatomic

two of the same element

2pz direction

points directly at other atom

diamagnetic

all electrons are paired

• weakly repelled in a magnetic field

paramagnetic

has unpaired electrons

• attracted to a magnetic field

in MO theory, orbitals need the same ___ to be mixed

symmetry

• related to whether sigma or pi bonds are formed

what p orbital forms sigma bonds?

2pz

which p orbitals form pi bonds?

2px and 2py

Valence Band

a band of orbitals that are filled or partially filled by valence electrons

Conduction Band

an unoccupied band higher in energy than a valence band, in which electrons are free to migrate

• kind of the opposite of valence band

metalloids

elements with properties that are intermediate between metals and nonmetals, often appearing lustrous and brittle with variable electrical conductivity. Common metalloids include Boron (B), Silicon (Si), Germanium (Ge), Arsenic (As), Antimony (Sb), and Tellurium (Te)

band gap

the space between the conduction and valence bands

• affects conductivity- larger gap= less conductive

Semi-Conductors

Metalloids

• Critical for when we need to control the conductivity of a substance

• Conductivity can be increased through doping

Doping

• n-type: add electron-rich dopant atoms that contribute excess electrons

• p-type: add electron-poor dopant atoms that cause a reduction in the number of electrons