Chapter 7.1: The Nature of Light

Flashcards from Chapter 7.1 of Chemistry: The Molecular Nature of Matter and Change.

Electromagnetic radiation

Energy propagated by electric and magnetic fields that vary intensity as they move in waves

• Includes microwaves, radio waves, light, and x-rays

Wavelength (λ)

The variable that describes the distance a light wave travels in one cycle

• Measured in meters (m)

Frequency (ν)

The variable that describes how many complete light waves pass through a point per second

• Measured in cycles per second (s^-1) or hertz (Hz)

Speed (c)

The constant that describes how fast a light wave moves per unit time

• Measured in meters per second (m/s or ms^-1)

• For light, this is ≈ 3.00⋅10⁸ m/s

  • Shows the inverse relationship between wavelength and frequency, as c = λν

Amplitude

The variable that describes the height of a light wave, affecting intensity

• Can vary separately from frequency and wavelength

Electromagnetic spectrum

The continuum of radiant energy arranged in order of increasing wavelength

• Gamma ray, x-ray, and ultraviolet regions have the shortest wavelengths

• Visible light has slightly longer wavelengths

• Infrared radiation has long wavelengths and low frequency, experienced as heat

• Microwaves and radio waves have the longest wavelengths

Blackbody radiation

An observed phenomena where objects of higher temperature give off light at lower wavelength and higher intensity

Quantum theory

A proposed explanation of many light phenomena, declaring that light only emits certain quantities of energy

• Expressed by the formula E = nhv, where

  • E is the energy of radiation

  • n is the quantum number

  • h is Planck’s constant

  • v is the wavelength

Planck’s constant (h)

A constant relating the energy and frequency of a photon, equal to 6.626 ⋅ 10^-34 J⋅s

• Multiplied by the wavelength and quantum number integer n to demonstrate fixed instead of continuous quantities

Quantum

A fixed quantity of energy stating the smallest energy that can be emitted by light

• Sets n = 1 to receive ΔE = hv

Photoelectric effect

A phenomenon where monochromatic light of sufficient frequency emits a current, challenging the wave nature of light due to:

• A minimum threshold frequency (not intensity)

• No time lag (as energy is seemingly instantly transferred)

Photon theory

A proposed explanation for the photoelectric effect where light flows in particulate states called photons, with energy related to frequency, not amplitude

• States that E_photon = hv = ΔE_atom

• Explains the photoelectric effect via the need for minimum energy attained through frequency