The periodic table Flashcards
What is the Aufbau principle?
Electrons enter and fill lower-energy orbitals before filling higher-energy orbitals.
What is Pauli’s exclusion principle?
No two electrons in the same atom can be in the same quantum state. No two electrons can have the same set of 4 quantum numbers.
What is Hund’s Rule of Maximum Multiplicity?
When there are degenerate orbitals available, electrons will enter the orbitals singly and will only pair up when all of the orbitals are half filled. This avoids e-e repulsion and maximises the exchange energy (k) of the electronic configuration.
What are exchange energies?
This energy can be calculated based on the number of pairs of parallel spins that exist for electrons of equal energy in a given electronic configuration. The more exchanges possible, the more stable the arrangement.
Why does the 4s orbital fill and empty before the 3d?
The 4s orbital has a lower energy when empty than the 3d orbitals, and increases in energy above the 3d when filled.
Why does Chromium not fill according to the expected pattern and how does it differ?
Expected: 4s2 3d4, actual: 4s1 3d5. This is due to the higher exchange energy created in this configuration.
What is the difference between the 2s/2p orbitals in hydrogen and the 2s/2p orbitals in other electron systems?
The 2s/2p orbitals are degenerate in hydrogen but this is not the case for other electron systems.
