When 578 \(\mathrm{kJ} / \mathrm{mol}\) of energy is supplied, Al loses one valence electron. Write the electron configuration of the ion that forms.

The Aufbau principle is a fundamental guide for determining the electron configuration of an atom in its ground state. Think of it as a kind of rulebook that tells electrons where to 'sit' in an atom's 'theater' of electron energy levels. According to this principle, electrons fill orbitals starting at the lowest available energy level before moving on to higher levels.

For example, the electron configuration of an aluminum atom is \(1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{1}\). Here, the Aufbau principle dictates that the 1s orbital is filled with two electrons first, followed by the 2s and 2p orbitals, and so on, up to the 3p orbital, which is the furthest from the nucleus and at the highest energy level among the populated orbitals. When an aluminum atom becomes an ion by losing a valence electron, according to the principle, the electron is lost from the orbital at the highest energy level, which is the 3p orbital in this case.

Closely related to the Aufbau principle is Pauli's exclusion principle, which further refines the 'seating arrangement' within an atom. This principle states that no two electrons in an atom can have the same set of four quantum numbers. In simple terms, it means each 'seat' or orbital can hold a maximum of two electrons, and they must have opposite spins. It's like having a rule that says each seat is designed for two people, but they can't be facing the same direction.

When writing out the electron configuration for aluminum, \(1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{1}\), this principle explains why we cannot add a third electron to the 1s, 2s, 2p, or 3s orbitals. The Pauli's exclusion principle ensures that electrons are properly distributed among the available orbitals, and each orbital is filled with electrons of opposite spins.

Valence electrons are the outermost electrons of an atom and are paramount in dictating an atom's chemical properties and how it will react with other substances. These are the electrons involved when atoms form chemical bonds. For aluminum, with its electron configuration \(1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{1}\), the valence electrons are those in the outermost third shell: two in the 3s orbital and one in the 3p orbital.

When 578 kJ/mol of energy is supplied, aluminum can lose one valence electron. This changes the electron configuration, which now becomes \(1s^{2} 2s^{2} 2p^{6} 3s^{2}\) for the ion that forms, reflecting the fact that only the electrons in the 3s orbital are now the outermost valence electrons. Valence electrons are crucial for understanding both the reactivity of elements and the types of bonds that they can form with other elements in chemical reactions.