Chapter 6: Electronic Structure and Periodic Properties of Elements

Introduction to Electromagnetic Radiation

• Definition: Electromagnetic radiation (EM radiation) is a disturbance that travels through electric and magnetic fields, carrying energy.

• Importance in Chemistry:

  • EM radiation is used to probe atoms through spectroscopy. The wave properties of EM radiation are crucial in this method.

  • Electrons also exhibit wave properties, making it essential to understand EM radiation in studying atomic structure.

Wave Properties of Electromagnetic Radiation

• Wave Definition: A wave is an oscillation or periodic movement that transports energy from one point to another.

• Key Properties:

  • Wavelength (λ):

  • Symbol: λ (lambda)

  • Measured from crest to crest.

  • Units of length: meters (m), nanometers (nm).

  • Frequency (ν):

  • Symbol: ν (nu)

  • Definition: The number of wavelengths that pass a point in a specific amount of time (in seconds).

  • Unit: Hertz (Hz), also expressed as /s or s⁻¹.

  • Relationship between Wavelength and Frequency:

  • Speed of light equation:
    c =
    u imes ext{λ}
    where ( c = 3.00 \times 10^8 \text{ m/s} ).

  • If wavelength (λ) increases, frequency (ν) decreases, and vice versa.

Electromagnetic Spectrum

• Definition: The electromagnetic spectrum encompasses all types of EM radiation, defined by varying wavelengths and frequencies.

• Visible Light: Makes up a small portion of the electromagnetic spectrum with specific frequencies and wavelengths.

• Color Wavelength Ranges (in nm):

  • Red: 620–750

  • Orange: 590–620

  • Yellow: 570–590

  • Green: 495–570

  • Blue: 450–495

  • Indigo: 440–450

  • Violet: 380–440

Energy and Photons

• Quantization of Energy:

  • Energy of electromagnetic radiation is quantized and exists in discrete units called photons.

  • Photon Energy Formula:

  • E = h
    u

  • Substituting for frequency:
    E = \frac{hc}{\text{λ}}

  • Where ( h ) (Planck's constant) is 6.63 \times 10^{-34}\text{ J s}.

  • Each individual photon has minimal energy, but a stream of light consists of numerous photons leading to significant total energy.

• Energy and Frequency Relation:

  • High frequency (short wavelength) light (e.g., X-rays) possess high energy.

  • Low frequency (long wavelength) light (e.g., radio waves) possess low energy.

Summary of Key Points

• Electromagnetic radiation is crucial for understanding atomic structure and spectroscopy.

• Waves have distinct wavelengths and frequencies, exhibiting specific behaviors based on these properties.

• The electromagnetic spectrum includes various forms of radiation, with visible light being just a small segment.

• The concept of quantization is fundamental, leading to the understanding of photons and their energy relationships based on frequency and wavelength.