Atomic Structure and Periodicity Electromagnetic Radiation and Nature of Matter

Quantum Theory From Democritus to Einstein has come the modern atomic theory. From Democritus to Einstein has come the modern atomic theory. What is the nature of atoms? Remember Dalton’s theory? What is the nature of atoms? Remember Dalton’s theory?

Electromagnetic Radiation One way energy travel through space is via electromagnetic radiation. One way energy travel through space is via electromagnetic radiation. All forms of radiant energy have wavelike behavior. All forms of radiant energy have wavelike behavior.

Waves Waves have 3 characteristics: Waves have 3 characteristics: Wavelength Frequency Speed

Wave characteristics is the symbol for wavelength, the distance between two consecutive peaks. is the symbol for wavelength, the distance between two consecutive peaks. is the frequency and is number of waves that pass through a given point in space in 1 second. is the frequency and is number of waves that pass through a given point in space in 1 second. The speed of all electromagnetic radiation is the speed of light or c. The speed of all electromagnetic radiation is the speed of light or c.

Wavelength and Frequency The longer the wavelength, the shorter the frequency. The longer the wavelength, the shorter the frequency.   = c = c Units for are 1/sec or hertz, Hz. Units for are 1/sec or hertz, Hz.

Waves have energy! Microwaves passing through water transfer their energy to the water and eventually heating the water to boiling. Microwaves passing through water transfer their energy to the water and eventually heating the water to boiling. Fire transfers heat by infrared radiation. Fire transfers heat by infrared radiation. Which is higher energy? Red or blue light? Which is higher energy? Red or blue light?

Flame tests! Example: Example: Sr(NO 3 ) 2 gives off a red flame of 650 nm. Sr(NO 3 ) 2 gives off a red flame of 650 nm. What is its frequency? What is its frequency?

Answer = c or = c/ = c or = c/ = 6.50 nm x 10 2 = 6.50 nm x 10 2 C = x 10 8 m/s C = x 10 8 m/s 1 m = 1 x 10 9 nm 1 m = 1 x 10 9 nm = 4.61 x Hz = 4.61 x Hz

Nature of Matter 19 th century thought: Matter and energy are distinct. 19 th century thought: Matter and energy are distinct. Matter was made of particles. Matter was made of particles. Light was an energy that moved in waves. Light was an energy that moved in waves. With that the study of physics was complete, there would be no new information, or was there? With that the study of physics was complete, there would be no new information, or was there?

Max Planck Studied radiation of soft bodies heated to incandescence. (light) Studied radiation of soft bodies heated to incandescence. (light) Originally thought matter could absorb or emit any quantity of energy. Originally thought matter could absorb or emit any quantity of energy. Max found that the energy could only be gained or lost in whole number multipliers of the equation h Max found that the energy could only be gained or lost in whole number multipliers of the equation h

Planck’s Constant h is Planck’s constant and was found to equal x J  s. h is Planck’s constant and was found to equal x J  s. The change in energy for a system may be found by ΔE=nh The change in energy for a system may be found by ΔE=nh This equation states that energy is given off in packets or quantized. This equation states that energy is given off in packets or quantized. Each packet of energy is a quantum. Each packet of energy is a quantum.

Example The blue in fireworks is often from Copper (I) chloride heated to 1200°C. Blue light has a wavelength of 450 nm. What is the quantum of energy that may be emitted by light at 450 nm? The blue in fireworks is often from Copper (I) chloride heated to 1200°C. Blue light has a wavelength of 450 nm. What is the quantum of energy that may be emitted by light at 450 nm?

Answer ΔE=nh n=1 ΔE=nh n=1 = c/ = c/ = x 10 8 m/s = x 10 8 m/s 4.5 x m 4.5 x m =6.6x10 14 s -1