Q. Describe Electron Configurations and Orbital Diagrams?

Ans. Remember that the atomic number of an atom tells us the number of protons and electrons in the neutral atom. To assign each of these electrons to a specific orbital in an atom's electron configuration, we must following these two rules:

• Aufbau Principle: Electrons fill energy levels in an atom by completely filling one sublevel before moving to the next one of higher energy
• Hund's Rule: Within a given sublevel, electrons fill all available empty orbitals before pairing up with electrons in occupied orbitals. In other words, there is a maximum number of half-filled orbitals.

To write an atom's electron configuration, you can also use this diagram to help determine the specific order of the subshells that the electrons will fill:

This diagram arranges the orbitals in the order by which they are filled by successive electrons. Just start at the upper left corner, following the arrows, and work your way down as needed to assign orbitals to all the electrons in a given atom. Remember that each orbital holds two electrons, and that:

• an s subshell can hold a maximum of 2 electrons
• a p subshell can hold a maximum of 6 electrons
• a d subshell can hold a maximum of 10 electrons,
• an f subshell can hold a maximum of 14 electrons

We can, for example, designate two electrons in a 1s subshell as 1s², and six electrons in a 2p subshell as 2p⁶.