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⚛️Quantum Mechanics Unit 6 Review

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6.2 The radial and angular wavefunctions of the hydrogen atom

⚛️Quantum Mechanics
Unit 6 Review

6.2 The radial and angular wavefunctions of the hydrogen atom

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
⚛️Quantum Mechanics
Unit & Topic Study Guides

The hydrogen atom's wavefunction is like a 3D map of where an electron might be. It's split into two parts: one that shows how far the electron is from the nucleus, and another that shows its direction.

These parts are tied to quantum numbers, which are like the atom's ID. They tell us about the electron's energy, shape, and spin, helping us understand how electrons behave in atoms and molecules.

Physical Meaning of Wavefunctions

Separable Wavefunction Components

  • Hydrogen atom wavefunction separates into radial and angular components expressed as ψ(r,θ,φ) = R(r)Y(θ,φ)
  • R(r) represents radial function describing electron's distance from nucleus
  • Y(θ,φ) denotes spherical harmonic function describing spatial orientation of electron's orbital
  • Wavefunction squared |ψ(r,θ,φ)|² yields probability density of electron location in space
  • Radial wavefunction R(r) determines probability distribution of electron's distance from nucleus
  • Angular wavefunction Y(θ,φ) determines probability distribution of electron's angular position

Nodes and Quantum Numbers

  • Radial nodes occur where R(r) = 0, indicating zero probability density at specific distances from nucleus
  • Angular nodes form surfaces where Y(θ,φ) = 0, creating planes or conical surfaces of zero probability density
  • Number of radial nodes relates to principal quantum number n (n - l - 1)
  • Number of angular nodes depends on angular momentum quantum number l (l planes) and magnetic quantum number m (|m| conical surfaces)
  • Total number of nodes equals n - 1, combining radial and angular nodes
  • Quantum numbers n, l, and m uniquely define electron's quantum state in hydrogen atom

Angular Momentum and Spherical Harmonics

Quantum Numbers and Angular Momentum

  • Angular wavefunction Y(θ,φ) described by spherical harmonics, eigenfunctions of angular momentum operator
  • Angular momentum quantum number l ranges from 0 to n-1 (0, 1, 2, ...)
  • Magnetic quantum number m ranges from -l to +l in integer steps
  • Total angular momentum calculated as L = √[l(l+1)]ħ (ħ denotes reduced Planck constant)
  • z-component of angular momentum quantized as Lz = mħ
  • Orbital angular momentum vector precesses around z-axis, forming a cone shape
  • Magnitude of angular momentum remains constant while direction varies

Properties of Spherical Harmonics

  • Spherical harmonics exhibit specific symmetry properties (parity, rotational symmetry)
  • Parity of spherical harmonic given by (-1)^l (even l yields even parity, odd l yields odd parity)
  • Rotational symmetry around z-axis related to magnetic quantum number m
  • Complex spherical harmonics form basis for angular momentum eigenstates
  • Real spherical harmonics created by linear combinations of complex spherical harmonics
  • Real spherical harmonics often used to visualize atomic orbitals (p orbitals along x, y, z axes)
  • Angular probability distribution given by |Y(θ,φ)|², representing likelihood of finding electron at specific angles

Probability Density Distributions

Visualization Techniques

  • Probability density distribution represented by |ψ(r,θ,φ)|², combining radial and angular components
  • Three-dimensional probability density plots show electron density regions (isosurfaces, contour plots)
  • Isosurfaces represent constant probability density values in 3D space
  • Contour plots display probability density on 2D slices through 3D distribution
  • Radial probability distribution plots use r²|R(r)|² to show likelihood of finding electron at specific distance
  • Most probable radius for each quantum state revealed by peak in radial probability distribution
  • Color-coding often employed to represent probability density magnitude in visualizations

Orbital Shapes and Characteristics

  • s orbitals (l = 0) exhibit spherically symmetric probability distributions
    • 1s orbital has no nodes, highest probability density near nucleus
    • 2s orbital has one radial node, creating a shell structure
  • p orbitals (l = 1) display dumbbell-shaped probability distributions
    • Oriented along x, y, or z axes (px, py, pz)
    • One angular node (nodal plane) perpendicular to orbital axis
  • d orbitals (l = 2) show more complex "cloverleaf" patterns
    • Five d orbitals: dxy, dyz, dxz, dx²-y², dz²
    • Two angular nodes creating four lobes (except for dz² with unique shape)
  • f orbitals (l = 3) and beyond reveal increasingly intricate distributions
    • Seven f orbitals with complex shapes and multiple lobes
    • Higher angular momentum states show more angular nodes and intricate patterns