Introductory Chemistry Instructor: Dr. Yongmei Wang
Topic 2: Electron Configuration and Periodic Table
This topic will go into details to discuss the quantum mechanical understanding of motions of electrons
in atoms, which determine the reactivity and properties of atoms. The content of this topic is found in
chapter 3 and 4 in your current textbook. Under this topic you should focus on
1. Know how chemist specifies orbitals using quantum numbers; memorize the list of orbitals from
first shell n=1 up to at least n=5
2. Memorize the energy order of orbitals up to 5f for H atom and for multielectron atoms. Know
the similarity and difference between the two sets.
3. Able to write electron configuration of all elements and see the link between electron
configuration with periodic table
4. Understand the periodic change of properties in terms of your knowledge of electron
configuration. These properties include: atomic radius, ionization energy and electron affinity
The textbook also introduces a little bit on quantum mechanics and light as electromagnetic radiation.
You should therefore also able to do the following
1. Interconvert between wavelength and frequency of light
2. Calculate energy of photon associated with any electromagnetic radiation
3. Able to relate energy of photon and electron jumps between different energy levels –calculate
wavelength of light absorption or emission due to electronic transition.
The following text provides a guide on the content discussed in Topic 2.
The chemical reactivity of an element is determined by the electrons in the atom. In order to understand
the reactivity of atoms, we need to know how these electrons move inside an atom. Electrons are
subatomic particles. Whenever one tries to study the motion of these subatomic particles, the classical
physics is no longer applicable. The motions of electrons are governed by the quantum mechanics. In
quantum world, the motion of a particle is described by a wavefunction . The reason we need wave-
function to describe the motion of electron is that in quantum world, you cannot know precisely where
and how fast a particle travels simultaneously. You can only speak of “probability” of finding a particle in
certain space. A wavefunction gives us the probability of finding the particle in space. The essential
equation governing the motion of electron is given by the Schrodinger equation, H=E where H is
called Hamiltonia operator, and is the wavefunction and E is the energy of the electron. If you solve
the above equation for one electron in the H atom, you get a set of wavefunctions (or called orbitals)
that have different energies. These orbitals are named as 1s, 2s,