Problem 14 - Chemistry A Molecular Approach

Question

What are degenerate orbitals? According to Hund's rule, how are degenerate orbitals occupied?

Step-by-Step Solution

Answer

Degenerate orbitals have the same energy levels, and according to Hund's rule, they are occupied by electrons singly with parallel spins before pairing occurs.

Step 1: Understanding Degenerate Orbitals

Degenerate orbitals are orbitals that have the same energy levels. In an atom, electrons can occupy different orbitals that belong to the same subshell (such as 2p or 3d orbitals), and if those orbitals have the same energy, they are referred to as degenerate.

Step 2: Application of Hund's Rule

Hund's rule states that when electrons occupy degenerate orbitals, they must first fill each orbital singly with parallel spins before pairing up. This means that if there are multiple degenerate orbitals available, one electron will go into each orbital with its spin unpaired until all orbitals contain one electron. Only after that can additional electrons pair up with the first ones, filling the orbitals completely.

Key Concepts

Understanding Degenerate Orbitals

Orbitals are like the 'rooms' where electrons 'live' inside an atom, and when we talk about degenerate orbitals, we're referring to 'rooms' that have the exact same energy levels. This is similar to having several identically sized rooms on the same floor of a building; they're at the same level, so no room is 'higher' or 'lower' than the other. In atomic terms, when electrons are looking for a 'room' or orbital to occupy, they don't have a preference for any particular one among the degenerate orbitals because the energy is the same; it's like they don't have to climb stairs to choose between them.

Electron Configuration and Hund's Rule

Electron configuration is all about the arrangement of electrons in an atom. Now, imagine a rule in the dorms that says every student must get their own room before anyone has to share. This is what Hund's rule is like for electrons. When you have degenerate orbitals, Hund's rule comes into play: each electron will first fill its own orbital, like students taking separate rooms, and only after each orbital has one electron (with their 'spin'—a kind of intrinsic momentum—all pointing the same way), will electrons start to pair up in the same orbital. This ensures that the electrons are as spread out as possible which is kind of like ensuring each student has their own personal space before they have to start sharing.

Orbital Energy Levels

In an atom, energy levels can be thought of as the different floors in a high-rise building, with the ground floor being the least energy-demanding level. The various orbitals within these levels are like different apartments, and some are higher-end than others. In terms of energy, electrons will generally fill the 'lower floors' (lower energy orbitals) first before moving 'upstairs' (to higher energy orbitals). It's sort of like people generally preferring to live on lower floors so they don't have to climb the stairs unless necessary. Understanding this building-like structure of electron accommodation in an atom helps clarify why the arrangement of electrons is crucial in determining an element's chemical behavior.