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Arrangement of Electrons in Atoms I. The Development of a New Atomic Model BIG IDEA- Electrons have properties of both WAVES & PARTICLES! A. The Nuclear Atom and Unanswered Questions List three reasons scientists found Rutherford’s nuclear atomic model to be incomplete. His model did not explain 1. ______________________________________________________________________________________ 2. ______________________________________________________________________________________ 3. ______________________________________________________________________________________ Before the 1900’s, scientists thought light behaved only as waves. This belief changed when it was discovered that light also has particle-like characteristics. This is known as the wave-particle duality of light. B. Wave Nature of Light Electromagnetic radiation: The electromagnetic spectrum includes: Characteristic properties of light waves include (draw a wave below and label the parts): The significant feature of wave motion is its repetitive nature, which can be characterized by the measurable properties of wavelength and frequency. 1. Wavelength (m, cm, nm): -1 2. Frequency (s or Hz): ___________________________ and ________________________ are mathematically related to each other. For electromagnetic radiation, the relationship is……. Formula: Where c = speed of light = λ= ν= Wavelength and frequency are _______________________________ proportional. This means ______________________________________________________________________________________ ALL electromagnetic waves travel at the speed of light (in a vacuum). A light beam passing through a prism is refracted (bent), separating it into all of the colors of the rainbow called the _______________________________________________________________. 1. ROYGBIV: ________________________________________________________________________________ 2. Each color of light has its own _____________________ and ________________________ ; and therefore a different amount of energy. C. Particle Nature of Light Photoelectric effect: Planck’s quantum concept (1900) 1. By studying the heating of solid objects, his quantum concept concluded that matter can gain or lose _____________________________ only in small, specific amounts called ___________________. A quantum is the minimum amount of energy that can be ______________________ or ________________________ by an atom. 2. A direct proportion exists between the energy of a quantum and the frequency of the emitted radiation: Formula: Where E= _______________________________; the unit for energy is __________________ h= Planck’s constant = _______________________________________ ν = _____________________________; the unit is ___________________ Einstein and the photoelectric effect (1905) 1. Einstein proposed that EM radiation has both wavelike and particle-like behavior. He explained that in addition to its wavelike characteristics, a beam of light can be thought of as a stream of ____________________________ called _____________________________. 2. Photon: 3. Einstein’s explanation of the photoelectric effect: Practice Problems: Problem/Work 1. Yellow light has a longer wavelength than green light. Which color of light has the higher frequency? 2. Green light has a lower frequency than blue light. What color of light has a longer wavelength? 3. Calculate the wavelength of yellow light emitted by a sodium lamp if the frequency of the radiation is 14 5.10 x 10 Hz. -7 4. Determine the frequency of light whose wavelength is 4.257 x 10 cm. 5. Calculate the energy, in Joules, of a quantum of radiant energy (the energy of a photon) that has a 15 -1 frequency of 5.00 x 10 s . 6. A photon has energy of 2.93 x 10 -25 J. What is its frequency? 7. A hydrogen line emission spectrum includes a line at a wavelength of 434 nm. What is the energy of this radiation? Answer D. Atomic Emission Spectra Define the following: ground state: excited state: emission: absorption: line- (or atomic-) emission spectrum: Each element’s atomic emission spectrum is __________________________ and can be used to identify that element. E. Bohr’s Model of the Atom Bohr constructed a model of the hydrogen atom with quantized energy levels that agreed with the hydrogen emission spectrum. Bohr’s model: 1. 2. 3. At first, Bohr’s model appeared promising; it fit the hydrogen atom very well, BUT ________________________________ ___________________________________it did NOT _______________. Electrons do ___________ move around the nucleus in circular orbits. His model did pave the way for later theories. F. Quantum Mechanical Model Mathematical laws can identify the regions outside of a nucleus where the electrons are __________________________ to be found. These laws are beyond the scope of this class and include the work of DeBroglie, Heisenberg, Schrodinger, and others. Like Bohr, the quantum mechanical model lead to quantized energy levels. Unlike Bohr, the quantum mechanical model does not define an exact pathway for electrons. The _____________________________________________________________ is concerned with the ______________________ of finding an electron. Today we say that the electrons are (most probably) located in a region outside the nucleus called the electron cloud.