 Presentation on theme: "Electromagnetic Radiation"— Presentation transcript:

Light Quantized energy Quantum theory and the atom

Light Wave nature of light Electromagnetic spectrum Equations

Wave Nature of Light All light is composed of an electric component and a magnetic component; thus the term electromagnetic radiation

Wave Nature of Light There are a few terms that we use to characterize light waves Wavelength (l) Units are meters (m) Frequency (n) Units are Hertz (Hz = seconds -1) Amplitude

Wave Nature of Light There are a few terms that we use to characterize light waves

Wave Nature of Light 3.0 x 108 m/s
Although light waves can have different wavelengths and frequencies, they all travel at the same speed; the speed of light 3.0 x 108 m/s

Electromagnetic Spectrum
Remember when we learned about radiation energy we looked at the electromagnetic spectrum Now we will apply the ideas of wavelength and frequency to the electromagnetic spectrum

Electromagnetic Spectrum

Electromagnetic Spectrum

Electromagnetic Spectrum
Visible light

Electromagnetic Spectrum
The frequency and wavelength of light are indirectly proportional As one increases, the other decreases

Equations The frequency and wavelength of light are indirectly proportional When frequency and wavelength are multiplied together, they always equal the speed of light Speed of light (c) c = l n

Equations If we know either the wavelength or the frequency of light, we can calculate the other one by rearranging the equation Ex: If we know the wavelength, n = c/l If we know the frequency, l = c/n

Quantized energy

Quantized Energy Particle nature of light
Emission and absorption spectra

Particle Nature of Light
Certain observations about light interacting with matter were not able to be described by the wave properties of light Heated objects emit light at specific frequencies at a given temperature When light of a certain frequency is shined on some metals, electrons are emitted

Particle Nature of Light
Max Planck, a German physicist, discovered that matter can only gain or lose energy in small specific amounts called quanta A quantum is the minimum amount of energy that can be gained or lost by an atom

Particle Nature of Light
The energy (E) that is emitted by hot objects is related to the frequency (n) of the emitted radiation. They are related by a number called Planck’s constant (h) h = e-34 J x s E = h n

Particle Nature of Light
h = e-34 J x s Energy is always released in multiples of h n (1 h n, 2 h n, 3 h n, ) E = h n

Particle Nature of Light
When light of a certain frequency is shined on a metal surface, electrons are ejected from the metal. This phenomenon is known as the photoelectric effect

Particle Nature of Light
Photoelectric effect Packets of light energy called photons Energy of light is transferred to the electron increasing the electron’s kinetic energy

Particle Nature of Light
Photoelectric effect

Particle Nature of Light
Atomic emission spectra

Particle Nature of Light
Atomic emission spectra Electricity passing through the neon gas in the glass tube Neon atoms absorb that energy and become “excited” The “excited” atoms release energy as light as they return back to their “ground” state The atomic emission spectra for an element is the set of frequencies of the light emitted by the atoms as they return to their “ground” state

Particle Nature of Light
Atomic emission spectra If the light emitted by an element is passed through a prism, the frequencies of the emitted light can be determined

Particle Nature of Light
Atomic emission spectra

Particle Nature of Light
Atomic emission spectra Atomic emission spectra Continuous emission spectra

Particle Nature of Light
Atomic emission spectra Each element has its own unique emission spectra

Particle Nature of Light
Absorption spectra

Particle Nature of Light
Continuous vs. emission vs. absorption “Excited” gas “Ground state” gas

Particle Nature of Light
We don’t see the colors that are absorbed, only those that are reflected

Particle Nature of Light
We don’t see the colors that are absorbed, only those that are reflected

Particle Nature of Light

Particle Nature of Light
Why do you think this pattern occurs?

Quantum theory and the atom

Quantum Theory and the Atom
Bohr’s model of the atom Electrons as waves Heisenberg uncertainty principle

Quantum Theory and the Atom
Bohr used Planck’s idea of quantized energy and applied it to the atom He proposed that electrons orbit nuclei only at specific distances from the nucleus

Quantum Theory and the Atom
Bohr atomic model

Quantum Theory and the Atom
Bohr atomic model The orbital closest to the nucleus corresponds to the ground state The orbitals further away from the nucleus are excited states

Quantum Theory and the Atom

Quantum Theory and the Atom
Energy associated with electron orbital transitions

Quantum Theory and the Atom
Energy associated with electron orbital transitions DE = Ef – Ei If E is absorbed, Ef > Ei DE is positive If E is emitted, Ef < Ei DE is negative

Quantum Theory and the Atom
Energy absorbed or emitted can be in frequencies other than just visible light

Quantum Theory and the Atom
De Broglie proposed that electrons moving around the nucleus had wave-like behavior. The wavelength associated with an electron depends on the mass and velocity of the electron l = h / m v

Quantum Theory and the Atom
The idea of particle – wave duality applies to all matter, not just light and electrons The mass of objects we can see are so large and the wavelengths are so small that we cannot see this effect l = h / m v

Quantum Theory and the Atom
Heisenberg uncertainty principle (for atomic scale particles) It is impossible to know both the position and the velocity of a particle at the same time

Quantum Theory and the Atom
Anything we do to determine the location or velocity of an electron moves it from its original location and changes its velocity We can know one or the other but not both We talk about the probability for an electron to occupy a certain region around the nucleus (so the fixed orbital proposed in the Bohr model are impossible)