Chem 11, Unit 8: Lewis Electron Dots, VSEPR (D, E)

Electron dots

-Represents the number of electrons in the outermost s and/or p orbitals (valence electrons)

-Written in pairs on each side of the atomic symbol

Atomic symbol in a dot diagram

Represents the nucleus and inner shells of electrons

Octet rule

Most bonded non-metallic elements have atoms with 8 electrons in their outermost energy levels (Exceptions include H)

How to determine the bonding of a molecule:

a) Determine the bonding experimentally

b) Make an assumption

When drawing Lewis dot diagrams, assume that...

-The single atom is in the middle if the formula if in the form AXn

-Molecules will form the most symmetrical shape possible

What does NAS stand for

-N: Needed (how many electrons in total must the atoms share)

-A: Available (what is the total number of valence electrons in all the atoms)

-S: Shared (how many electrons are shared)

Limitation of the electron dot model

Doesn't explain bonds which are in between single, double, and triple bonds

Elements that don't require 8 electrons in their bonded orbitals

H (2e-), Be (4e-), B (6e-)

Exceptions

-Some compounds involve binding with d orbitals in addition to the s and p orbital electrons (can have more than 8 bonded electrons)

-Some compounds can't be explained using this method and require more sophisticated bond theories (Example: half bonds)

What does VSEPR stand for

Valence Shell Electron Pair Repulsion

VSEPR Theory

-Used to predict the shapes of molecules

-Bonded atoms and lone pairs of electrons are arranged around a central atom as far as possible to minimize repulsion