Assign a set of four quantum numbers for the outermost two electrons in Sr.

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Step 1: Identify the atomic number of Sr (Strontium). The atomic number of Sr is 38, which means it has 38 electrons in its neutral state.

Step 2: Write the electron configuration for Sr. The electron configuration of Sr is [Kr] 5s2. This means that the last two electrons (the outermost electrons) are in the 5s orbital.

Step 3: Assign the quantum numbers for the 5s orbital. The principal quantum number (n) is 5, the azimuthal quantum number (l) is 0 (for s orbital), and the magnetic quantum number (ml) can be 0 (since l=0, ml can only be 0).

Step 4: Assign the spin quantum numbers (ms) for the two electrons. The first electron will have a spin quantum number of +1/2 and the second electron will have a spin quantum number of -1/2.

Step 5: The set of four quantum numbers for the outermost two electrons in Sr are therefore (5, 0, 0, +1/2) and (5, 0, 0, -1/2).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Quantum Numbers

Quantum numbers are a set of four numbers that describe the unique quantum state of an electron in an atom. They include the principal quantum number (n), azimuthal quantum number (l), magnetic quantum number (m_l), and spin quantum number (m_s). Each electron in an atom is characterized by these quantum numbers, which determine its energy level, shape, orientation, and spin.

Electron Configuration

Electron configuration refers to the distribution of electrons in an atom's orbitals. For strontium (Sr), which has an atomic number of 38, the electron configuration is [Kr] 5s². This indicates that the outermost two electrons occupy the 5s orbital, which is crucial for determining their quantum numbers.

Pauli Exclusion Principle

The Pauli Exclusion Principle states that no two electrons in an atom can have the same set of four quantum numbers. This principle is essential for assigning quantum numbers to electrons, ensuring that each electron in the outermost shell of strontium has a unique combination of quantum numbers, particularly in terms of their spin.

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