UNIT 3 ELECTRON CONFIGURATION AND MODERN ATOMIC THEORY

Section 1: Light and Quantized Energy

Development of Atomic Models These illustrations show how the atomic model has changed as scientists learned more about the atom’s structure.

Development of Atomic Models Rutherford’s Model: - didn’t explain how the electrons are arranged around the nucleus. - didn’t explain why negatively charged electrons aren’t pulled into the positively charged nucleus.

Development of Atomic Models In the early 1900s, scientists observed that certain metals and compounds of metals emitted visible light when heated in a flame. - Studies of absorption and emission of light revealed an intimate relationship between light and an atom’s electrons.

The Wave Nature of Light - Visible light is a type of electromagnetic radiation, a form of energy that exhibits wave-like behavior as it travels through space. - All waves can be described by several characteristics.

The Wave Nature of Light amplitude: wave’s height from zero to crest. wavelength,  : distance between the crests. frequency,  : number of wave cycles to pass a point per unit of time (measured in Hz or s-1). All EM waves travel at the same speed!

The Wave Nature of Light The frequency and wavelength of light waves are inversely related. As the wavelength increases, the frequency decreases. wavelength and frequency are inversely proportional to each other

The Wave Nature of Light R O Y G B I V

The Wave Nature of Light c = 3  108 m/s (speed of light) c = λν wavelength and frequency are inversely proportional λ is wavelength ν is frequency All EM radiation travels at the same speed!!!

c = λn Sample Calculation 1: Calculate the wavelength of the yellow light emitted by a sodium lamp if frequency of the radiation is 5.10 x 1014 Hz. (3.00 x 108) = λ (5.10 x 1014) (3.00 x 108) = λ (5.10 x 1014) λ = 5.88 x 10–7 m

c = λn Sample Calculation 2: Calculate the frequency of blue light with a wavelength of 6.05 x 10–7 m (or 605 nm). (3.00 x 108) = (6.05 x 10–7) n (3.00 x 108) = n (6.05 x 10–7) n = 4.96 x 1014 s–1

The Particle Nature of Light The wave model of light cannot explain all of light’s characteristics. Why do certain materials, like iron, emit only specific colors of light when heated? Why don’t they give off a continuous spectrum of light?

The Particle Nature of Light The wave model of light cannot explain all of light’s characteristics. Photoelectric Effect Why do some metals emit electrons only when light of a specific minimum frequency shines on them?

The Particle Nature of Light German physicist Max Planck discovered that 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. - Planck’s Constant has a value of 6.63  10–34 J ● s.

The Particle Nature of Light - Albert Einstein proposed in 1905 that light has a dual nature. - A beam of light has wave-like and particle-like properties. - A photon is a particle of electromagnetic radiation with no mass that carries a quantum of energy.

The Particle Nature of Light E = energy in joules (J) E = hν energy and frequency are directly proportional h is Planck’s constant (6.6 3 x 10-34) ν is frequency in Hz

E = hn Sample Calculation 3: Calculate the energy of the yellow light emitted by a sodium lamp if frequency of the radiation is 5.10 x 1014 Hz. E = (6.63 x 10–34) (5.10 x 1014) E = 3.38 x 10–19 J Sodium vapor lamps produce a yellow glow.

E = hn c = λn Sample Calculation 4: Calculate the energy of blue light with a wavelength of 6.05 x 10–7 m (or 605 nm). (3.00 x 108) = (6.05 x 10–7) n (3.00 x 108) = n (6.05 x 10–7) n = 4.96 x 1014 s–1 Sodium vapor lamps produce a yellow glow. E = (6.63 x 10–34) (4.96 x 1014) E = 3.29 x 10–19 J

Quick Quiz! 1. Which of the following relationships is true? A. Higher-energy light has a higher frequency than lower-energy light does. B. Higher-energy light has a longer wavelength than lower-energy light does. C. Higher-energy light travels at a faster speed than lower-energy light does. D. Higher-frequency light travels at a slower speed than lower-energy light does.

Quick Quiz. 2. The energy of EM radiation is greatest for A. visible light. B. ultraviolet light. C. infrared light. D. X-ray radiation.

Quick Quiz. 3. The longer the wavelength of light, the… A. higher the frequency. B. higher the energy. C. lower the energy. D. lower the frequency.