Quantum Theory and the Electronic Structure of Atoms Chapter Seven Quantum Theory and the Electronic Structure of Atoms

Wave: a vibrating disturbance by which energy is transmitted. Chapter Seven / Quantum Theory and the Electronic Structure of Atoms From Classical Physics to Quantum Theory We have to understand something about the nature of wave before talking about Quantum theory. Wave: a vibrating disturbance by which energy is transmitted.

Frequency is measured in hertz (Hz) 1 Hz = 1 cycle/s Chapter Seven / Quantum Theory and the Electronic Structure of Atoms From Classical Physics to Quantum Theory Wavelength (λ) lambda: is the distance between identical points on successive waves. Frequency (ν) nu: is the number of waves that pass through a particular point in 1 second. Amplitude : is the vertical distance from the midline of a wave to the peak. Wave speed (u): depend on type of wave and the nature of the medium through which the wave is traveling. u = λν Wavelength usually expressed in units of meter, centimeter, or nanometer. Frequency is measured in hertz (Hz) 1 Hz = 1 cycle/s Normally the word cycle is left out and we say and we expressed frequency as for example 25/s

The speed of light is known as 3 x 108 m/s Chapter Seven / Quantum Theory and the Electronic Structure of Atoms From Classical Physics to Quantum Theory Example: The wavelength of the green light from a traffic signal is centered at 522 nm. What is the frequency of this radiation? u =λν ν=u/λ The speed of light is known as 3 x 108 m/s Because the speed light in m we have to change the wavelength to m λ = 522 x 10-9 m ν = 3 x 108 / 522 x 10-9 = 5.75 x 1014 Hz.

for all electromagnetic radiation c = λν Chapter Seven / Quantum Theory and the Electronic Structure of Atoms From Classical Physics to Quantum Theory There are many type of waves, such as water waves, sound waves and light waves. Clerk Maxwell proposed in 1973 that visible light consists of electromagnetic wave has an electric field component and a magnetic filed component. The two components have the same wavelength and frequency, and hence the speed. Electromagnetic radiation is the emission and transmission of energy in the form of electromagnetic waves. for all electromagnetic radiation c = λν Where c is the speed of light = 3 x 108 m/s

From Classical Physics to Quantum Theory Chapter Seven / Quantum Theory and the Electronic Structure of Atoms From Classical Physics to Quantum Theory

Chapter Seven / Quantum Theory and the Electronic Structure of Atoms From Classical Physics to Quantum Theory Example: A photon has a frequency of 6.0 x 104 Hz. Convert this frequency into wavelength (nm). Does this frequency fall in the visible region? c = λν λ = c/ν = 3 x108 / 6 x104 =5 x 103 m = 5 x 1012 nm Radio wave

The energy of a signal quantum (E): Chapter Seven / Quantum Theory and the Electronic Structure of Atoms Planck’s Quantum Theory When solid are heated they emit electromagnetic radiation over a wide range of wavelength. Example is the dull red glow of an electric heater and the bright white light of tungsten light bulb. the amount of radiant energy emitted by an object at a certain temperature depends on the wavelength according to Plank the atoms and molecules could emit (or adsorb) energy only in discrete quantities (quantum). Quantum is the smallest quantity of energy that can be emitted (or absorbed) in the form of electromagnetic radiation. The energy of a signal quantum (E): Where h is planck’s constant

Chapter Seven / Quantum Theory and the Electronic Structure of Atoms Planck’s Quantum Theory According to the quantum theory energy is always emitted in integral multiples of hν, for example hν, 2hν, 3hν, …… but never for exmaple 1.67hν. Example: Calculate the energy (in J) of: (a) a photon with a wavelength of 5.00 x 104 nm (IR region) (b) a photon with a wavelength of 5.00 x 10-2 nm (X-ray region) a-λ= 5 x 104nm = 5 x 104 x 10-9 = 5 x 10-5m

Chapter Seven / Quantum Theory and the Electronic Structure of Atoms Planck’s Quantum Theory b- λ= 5 x 10-2 nm = 5 x 10-2 x 10-9 = 5 x 10-11m

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