Chemistry- Chapter 8-> Section 8.1

Lewis structures show , but Lewis structures can't so they came up with two new models: the bond theory and the orbital theory.

Valence bond theory: a model of chemical bonding that states that atoms fill their valence shells by filling vacancies in particular . Partially filled orbitals of two atoms , and a bond is formed. This theory is also called the electron theory.

Sigma bonds: The orbitals overlap to end. The orbital overlap is located the nuclei. They can form from various orbital combinations: two s orbitals, two p orbitals, or an s and a p orbital. Sigma bonds always form .

Pi bonds: The orbitals overlap to side. The orbital overlap is located above and the nuclei. Pi bonds can combine with bonds and other pi bonds to form and triple bonds. One sigma and one pi= (double bond.) One sigma and two pi= ( bond.) Pi bonds always form sigma bonds.

Sigma bonds are the . Pi bonds are than sigma bonds because the electrons are spread out over a greater volume of space around the bond axis. The combination of a sigma and a pi bond is than either bond by itself.

Resonance: the state of molecules that can have or more possible Lewis structures. No Lewis structure can completely describe electron distribution in resonance molecules. There are NO single or double bonds in these molecules- the bonds are experimentally identical. A resonance molecule is depicted with a Lewis structure.

Some molecules form without an octet for each bonded atom: this happens when there is an number of valence electrons, electron , and hypervalent molecules.

Some molecules have an odd number of valence electrons to share. Substances with these unpaired electrons are called and tend to be fairly .

Electron Deficiency: elements with than 8 valence electrons.

Hypervalent Molecules: The central atom has than 8 valence electrons. This occurs only in Period and higher. These molecules are described as having octets.

The Molecular Orbital Theory: the orbitals of an atom are replaced by orbitals when a molecule forms. Each molecule has a set of molecular orbitals equal to the of the atomic orbitals of the original atoms. Molecular orbitals are much than atomic orbitals, up to the size of the entire molecule. Orbitals are ranked in order of energy.

: the attraction of a molecule to a magnetic field

Factors affected by the arrangement of a molecule's electrons:
- bond (bonding and antibonding)
- bond (single, double, triple bonds)
- molecular properties (like paramagnetism)

Bonding orbitals:
- interference
- nuclei
- in energy than the atomic orbitals from which they form
- stable molecules

Antibonding orbitals:
- interference
- of the molecule, far away from the nuclei
- in energy than the atomic orbitals
- unstable