Ch 1 : Electrons and Orbitals

Chapter 1: Where are the Electrons ?

Atomic Orbitals

The electron is the subatomic particle that is fundamental to chemical bonding. For atoms, the electrons are associated with atomic orbitals and it is convienient to think of finding the electrons in the atomic orbitals. But what about electrons in molecules ? Before we can talk about that, we should make sure we understand where they are in atoms. As we will see later, the important principles that apply to atomic orbitals also apply to molecular orbitals.

Simply put, chemical reactions are about reorganising bonds
And bonds are due electrons
So that means chemistry is all about electrons.

STUDY TIP
Learn to keep track of electrons !
Pay attention to charges.
You will find that if you know where the electrons are and what they are doing, then it is much easier to master organic chemistry.

Electrons were discovered in 1897 by J.J. Thompson. They are often thought of as particles. But in 1924, De Broglie suggested that electrons also have wave like properties. This is the concept of "wave-particle duality".

QUESTION : Can you think of examples of particle type and wave type properties ? ANSWER

In 1926, Schrodinger showed that electrons in a hydrogen atom could be described by a wave function, Y.

Electrons are often described as being in orbitals around an atom that are mathematical "constructs" based on the wave function, Y, that describes the motion of an electron.
An orbital is, more correctly, a mathematical function, 4pr²Y², that describes the region of high probability in 3D space, around a nucleus, where an electron is most likely to be found.
Orbitals are commonly represented by the "boundary" surfaces that encloses the region where there is a 90-95 % probability of finding the electron.

In organic chemistry which is focussed on carbon, one needs to be most familiar with the s- and p-type orbitals.

Orbitals can be described by using quantum numbers which arise from the quantum mechanics and wave functions.