An orbital diagram visually represents the distribution of electrons in an atom’s orbitals, while an electron configuration provides a written notation of the electron arrangement. Let’s break this down further, focusing on the principles governing these arrangements: the Pauli Exclusion Principle, the Aufbau Principle, and Hund’s Rule.
1. Pauli Exclusion Principle:
According to this principle, no two electrons in an atom can have the same set of quantum numbers. In an orbital diagram, this is illustrated by showing that each orbital can hold a maximum of two electrons, which must have opposite spins. For instance, in the 1s orbital diagram, you would see the first electron represented with an upward arrow (↑), and if a second electron is added, it would be shown with a downward arrow (↓) in the same orbital. This ensures that each electron is paired with one of opposite spin.
2. Aufbau Principle:
This principle states that electrons occupy the lowest energy orbitals available before filling higher energy orbitals. In an orbital diagram, you would start filling orbitals in order of increasing energy. For example, the 1s orbital is filled first, followed by the 2s orbital, and then the 2p orbitals. You would depict the 1s filled with two electrons before you start filling the 2s and subsequent orbitals. This sequential filling is essential for determining the correct electron configuration.
3. Hund’s Rule:
Hund’s Rule states that electrons will fill degenerate orbitals (orbitals of the same energy, such as the three 2p orbitals) singly before pairing up. In an orbital diagram, this is depicted by placing one electron in each of the degenerate orbitals before any of them receive a second electron. For example, in the 2p subshell, you would fill it as follows: one electron goes into each of the three 2p orbitals (2px, 2py, and 2pz) before any of them gets a second electron.
Sample Orbital Diagram Problems:
1. For Carbon (atomic number 6): The orbital diagram would look like this:
1s: ↑↓ 2s: ↑↓ 2p: ↑ ↑
This shows that the first two electrons fill the 1s, the next two fill the 2s, and the remaining two occupy separate 2p orbitals according to Hund’s Rule.
2. For Oxygen (atomic number 8): The orbital diagram is:
1s: ↑↓ 2s: ↑↓ 2p: ↑ ↑ ↓
Here, the two 2p electrons pair in one of the degenerate orbitals after each gets one electron, following Hund’s Rule.
In summary, while the electron configuration gives a shorthand representation of the electron arrangement, orbital diagrams provide a clear visual representation that emphasizes the principles that dictate electron pairing and filling order in atoms.