Overview
This lecture introduces the nature of light, the basics of quantum mechanics, and the four quantum numbers used to describe the electronic structure of atoms.
Nature of Light
- When hydrogen is heated, it emits light composed of specific colors, each with a particular wavelength.
- Neils Bohr proposed electrons occupy fixed energy levels and light is emitted when they transition between these levels.
- Light is made of oscillating electric and magnetic fields, characterized by wavelength (λ) and frequency (ν).
- The equation c = λν relates light’s speed (c), wavelength (λ in meters), and frequency (ν in Hz).
- Max Planck showed electromagnetic radiation comes in quantized energy units, called quanta.
- Energy of a photon: E = hν, where h is Planck's constant (6.63 × 10⁻³⁴ J·s).
- Alternate energy formula: E = (hc)/λ.
Quantum Mechanics & Electron Structure
- Quantum mechanics describes the behavior and location of electrons in atoms.
- Schrödinger’s wave equation predicts the probability of finding an electron in a region called an orbital.
- Each electron is described by four quantum numbers: principal (n), angular momentum (l), magnetic (ml), and spin (ms).
Quantum Numbers (P.A.M.S.)
- Principal quantum number (n): main energy level (shell), allowed values are positive integers (n = 1, 2, 3...).
- Angular momentum quantum number (l): orbital shape, allowed values are 0 to n-1; l = 0 (s orbital), 1 (p), 2 (d), 3 (f).
- Magnetic quantum number (ml): specifies orbital orientation, allowed values: –l to +l (including zero).
- Spin quantum number (ms): electron spin, only two values allowed: +½ or –½.
Electron Shells and Subshells
- The number of l values in a shell defines the subshells it contains.
- Each ml value represents an orbital; each orbital holds up to 2 electrons with opposite spins.
- Maximum electrons in a shell = 2n².
- Example: K shell (n=1) holds 2 electrons; L shell (n=2) holds 8 electrons; M shell (n=3) holds 18 electrons.
Key Terms & Definitions
- Wavelength (λ) — Distance between peaks in a wave; measured in meters.
- Frequency (ν) — Number of wave cycles per second; measured in hertz (Hz).
- Photon — Quantum of electromagnetic radiation.
- Quantum Numbers — Set of four numbers describing electron position and behavior.
- Orbital — Region where there is high probability of finding an electron.
- Subshell — Group of orbitals with the same l value within a shell.
Action Items / Next Steps
- Download and complete Activity 1 (practice questions) from Courselink.
- Review the table of allowed quantum numbers and practice electron configurations for M and N shells.
- Attend or watch the recorded tutorial on Activity 1.
- Email instructor with questions or request a virtual meeting if needed.