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Pauli

Hund's rule states that electrons will singly occupy degenerate orbitals before pairing up. This is because electrons repel each other due to their negative charge and prefer to stay farther apart. The Pauli exclusion principle specifies that no two electrons in an atom can have the same set of four quantum numbers, meaning each electron's state is unique. For the given electron configuration of 3s2 3p4, Hund's rule dictates that the first three 3p electrons will singly occupy each of the three 3p orbitals with parallel spins, while the fourth electron pairs up with one of the occupied orbitals with opposite spin.

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82 views2 pages

Pauli

Hund's rule states that electrons will singly occupy degenerate orbitals before pairing up. This is because electrons repel each other due to their negative charge and prefer to stay farther apart. The Pauli exclusion principle specifies that no two electrons in an atom can have the same set of four quantum numbers, meaning each electron's state is unique. For the given electron configuration of 3s2 3p4, Hund's rule dictates that the first three 3p electrons will singly occupy each of the three 3p orbitals with parallel spins, while the fourth electron pairs up with one of the occupied orbitals with opposite spin.

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San Nwe Zin
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Pauli's Exclusion Principle states that no two electrons in the same atom can

have identical values for all four of their quantum numbers. In other words, (1)
no more than two electrons can occupy the same orbital and (2) two electrons
in the same orbital must have opposite spins

Hund's Rule
 Definition: Hund's rule postulates that electrons will populate degenerate
orbitals (orbitals with the same energy level) singly before any orbital is doubly
occupied.
 Implications for Electron Filling:
 Electrons are like people; they require their own space. When multiple
rooms (orbitals) are available, they'll first occupy separate rooms
before sharing. Similarly, electrons fill all the degenerate orbitals singly
before pairing up.
 This behaviour is rooted in the electron's inherent negative charge.
Electrons repel each other due to like charges. By occupying separate
orbitals, they minimise this repulsion, leading to a more stable atomic
configuration.
 Electron Repulsion: The concept of electron repulsion is central to Hund's
rule. Electrons, being negatively charged, naturally repel each other. When
given a choice, they prefer to stay as far apart as possible, leading to the
observed behaviour of singly filling degenerate orbitals before pairing up.
 Example: Oxygen, with its six electrons in the 2p and 2s orbitals, will have two
unpaired electrons in the 2p orbitals, adhering to Hund's rule.

Pauli Exclusion Principle


 Definition: The Pauli exclusion principle, introduced by physicist Wolfgang
Pauli in 1925, states that no two electrons in an atom can share all four of
their quantum numbers. Essentially, this means that each electron in an atom
has a unique set of quantum numbers.
 Implications for Electron Filling:
 The principle ensures that each atomic orbital can accommodate a
maximum of two electrons, and these electrons must have opposite
spins. This is visually represented by up and down arrows in orbital
diagrams.
 The significance of this principle extends beyond just electron filling. It
ensures the uniqueness of each electron's state in an atom,
contributing to the atom's overall stability.
 Quantum Numbers Explained: Electrons in an atom are characterised by four
quantum numbers:
 Principal Quantum Number (n): Represents the main energy level or
shell.
 Azimuthal Quantum Number (l): Denotes the shape of the orbital (s, p,
d, f).
 Magnetic Quantum Number (m): Specifies the orientation of the orbital
in space.
 Spin Quantum Number (s): Indicates the spin of the electron (either +½
or -½).
An atom's electron configuration is represented as 1s² 2s² 2p⁶ 3s² 3p⁴. Using Hund's
rule and the Pauli exclusion principle, describe the arrangement of electrons in the
3p orbitals.
For the give electron configuration, the 3p subshell contains four electrons.
According to Hund's rule, electrons will singly occupy degenerate orbitals before
pairing up. Therefore, in the three available 3p orbitals (3px, 3py, and 3pz), the first
three electrons will singly occupy each orbital. The fourth electron will then pair up
with one of the previously occupied orbitals. Using the Pauli exclusion principle, this
paired electron will have an opposite spin to the first. Thus, two of the 3p orbitals will
have one electron, each with parallel spins, and one 3p orbital will have two
electrons with opposite spins.

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