Light and Energy Electromagnetic Radiation is a form of energy that is created through the interaction of electrical and magnetic fields. It displays wave-like behavior as it travels through space.

Light and Energy Several characteristics can be used to describe these waves. Frequency (n) is the number of waves that pass a given point per second. 2 sec Amplitude (a) is the height of a wave from the normal to the cresting point. Time Wavelength (l) is the total distance that encompasses a full crest and a full trough.

f2 has a higher frequency. Light and Energy Which of the following waves has a higher frequency? f2 has a higher frequency.

Light and Energy All electromagnetic waves travel at the same speed in a vacuum This speed (c) is 3.00 x 108 m/s in a vacuum. c is more commonly referred to as the speed of light. c = ln

As the wavelength decreases, the frequency increases and the energy….. Light and Energy Electromagnetic radiation can be displayed in the electromagnetic spectrum. This spectrum places all of the wave types in order based on wavelength (l) and frequency (n). As the wavelength decreases, the frequency increases and the energy….. INCREASES!

Light and Energy In 1900 Max Planck helped us move toward a better understanding of electromagnetic radiation. Matter can gain or lose energy only in small, specific amounts called quanta. A quantum is the minimum amount of energy that can be gained or lost by an atom.

How can we equate wavelength and energy? Light and Energy Planck then demonstrated the relationship between that quantum and the frequency of the emitted radiation. E = hn E = energy n = frequency h = Planck’s Constant 6.626 x 10-34 J s c = ln E = hn How can we equate wavelength and energy?

Light and Energy Wave Theory of Light In the 1800’s Thomas Young conducted an experiment on the wave theory of light.

Light and Energy Double Slit Interference Patterns

This proved that light had wave properties.

Light and Energy The wave theory of light could not explain why objects, when heated, would emit different colors of light at different temperatures These colors would correspond to different frequencies and wavelengths.

Light and Energy Light and energy can’t always be explained using waves. In 1905 Albert Einstein proposed that electromagnetic radiation has both wavelike and particle like natures. In the photoelectric effect electrons (or photoelectrons) are emitted from a metal’s surface when light or energy of a specific frequency comes in contact with the metal.

Looking at an emission spectrum of a rainbow. Light and Energy Looking at an emission spectrum of a rainbow.

Light and Energy What was happening? 3-2 4-2 5-2 6-2 What was happening? When a photon ( a packet of light energy) is absorbed, an electron moves from a low energy level to a higher energy level. This change is energy results in the black lines that are seen. -When the electron returns to it’s original energy level, it emits energy in the form of a photon of light that has a specific frequency and wavelength. Are there other frequencies of radiation being emitted?

Light and Energy 3-2 4-2 5-2 6-2 Emission and Absorption spectrums are important because they are one of the most important ways chemists can probe atomic structure. This also led to the idea that energy was quantized. Electrons could only gain or lose energy in specific quantized amounts.

Light and Energy So, is light a wave or a particle? While a beam of light has many wavelike characteristics, the beam can also be thought of as a stream of tiny particles or bundles of energy called photons. In other words: A photon is a particle of electromagnetic radiation with no rest mass that carries a quantum of energy.

Atomic Theory Neils Bohr (1885 - 1962) Proposed a quantum model Predicted frequencies of hydrogen’s atomic emission spectrum Atoms have only certain allowable energy states Related energy states to the motion of electrons in circular orbits

Atomic Theory Bohr Model of an Atom Visible Infrared Ultraviolet

Atomic Theory Louis de Broglie So…. If light has both particle and wave properties, can objects that are particles have wave characteristics? Louis de Broglie

Atomic Theory Louis de Broglie (1892 – 1987) All moving particles, including electrons, have wave characteristics. Only whole numbers of wavelengths are allowed in a circular orbit of a fixed radius Electrons move in wavelike motion with restricted circular orbits

Atomic Theory The de Broglie equation predicts that all moving particles have wave characteristics. l = h /mv However, this wavelike nature is too small to be observed for macroscopic objects.

Atomic Theory Heisenberg Uncertainty Principle Stated that it is impossible to know both the position and velocity of an electron. This is because when attempting to observe an electron, the wavelength of light we would have to use will cause the electron to move.

Atomic Theory Schrodinger wave equation Erwin Schrodinger used de Broglie’s wave theory to develop the quantum mechanical model of the atom. Like Bohr’s model, the quantum mechanical model limits the electron’s energy to certain values, but it does NOT describe the path around the nucleus. It predicted the probable location of an electron in an atom. That location is more likely to be close to the nucleus.