(455) Nuclear physics and energy levels [IB Physics SL/HL]

Introduction

• Discussing nuclear physics and energy levels.

• Importance of understanding notation.

Simple Atom Structure

• Atoms consist of a central nucleus containing:

  • Neutrons (n)

  • Protons (p)

• Electrons orbit the nucleus; their details are temporarily less relevant.

• The nucleus is significantly smaller than the atomic structure, which is largely empty space.

Atomic Notation

• General representation: Element X

• Z (Atomic Number):

  • Located at the bottom.

  • Represents the number of protons in the nucleus.

  • Example: Helium (He) has 2 protons (Z = 2).

• Mass Number:

  • Top number indicating the total number of nucleons (protons + neutrons).

  • Example: Helium has a mass number of 4 (2 protons + 2 neutrons).

• Redundancy in notation:

  • Helium-4 vs Helium; atomic number is unnecessary if the element's name is known.

Energy Levels

• Electrons exist in quantized energy levels around the nucleus.

• Electrons can be excited by:

  • Absorbing photons

  • Applying potential difference (e.g. in fluorescent lights).

• Transitioning to lower energy levels results in photon emission.

• The relation:

  • E = hf

    • E = energy of the photon

    • h = Planck’s constant (6.63 × 10^-34 J·s)

    • f = frequency of the photon (Hertz)

• Photon energy is quantized and only exists in multiples of Planck's constant.

Energy Transitions

• Various transitions possible between energy levels.

  • Transition from higher to lower energy results in emitted light.

• Different photons emitted correspond to different energy differences:

  • Larger energy transition = higher frequency = different colors.

• Allowed frequencies and wavelengths are specific to the atom's structure.

Relationships Between Energy, Frequency, and Wavelength

• Wave equation relationship:

  • For light: c = fλ

    • c = speed of light

    • λ = wavelength

• Rearranging gives the wavelength as

  • λ = hc/E

    • Inversely proportional; higher frequency = smaller wavelength.

Example of Electron Transitions

• Transition causing the smallest wavelength corresponds to the largest frequency and energy:

  • Use E = hf principle to find the largest energy transition for smallest wavelength.

  • Example highlighted: Transition A has the largest energy, therefore the smallest wavelength.