Final answer:
Austrian physicist Wolfgang Pauli formulated the Pauli exclusion principle, which states that an orbital can hold a maximum of two electrons with opposite spins. This principle is fundamental in determining the electron configuration of elements like oxygen, with its four 2p electrons first filling each orbital singly before pairing up.
Step-by-step explanation:
The scientist who determined that every orbital can hold up to two electrons of opposite spins was Austrian physicist Wolfgang Pauli. This is known as the Pauli exclusion principle. It states that no two electrons in an atom can have the same set of all four quantum numbers, which means that two electrons can share the same orbital only if their spin quantum numbers (± ½) are opposite.
Using oxygen as an example, it has four 2p electrons. According to Hund's Rule, these electrons will first fill each 2p orbital singly with parallel spins. Once all the orbitals have one electron, any additional electrons will pair up with the opposite spin. Therefore, after each 2p orbital has one electron, the fourth electron can enter the first 2p orbital with a spin opposite to that of the already present electron.
Each atomic orbital can be occupied by a maximum of two electrons. This rule is also reflected in the way we determine the electron configuration of elements and their subsequent chemical behaviors. The number of orbitals in any shell 'n' is given by n², and with two electrons allowed per orbital, the maximum number of electrons in a shell can be calculated as 2 x n².