CHM120H5 Lecture Notes - Lecture 1: Bohr Model, Standing Wave, Vsepr Theory

LIGHT LAB SPRING 2018 CHEM 1430 Ill. Quantization of Electromagnetic Radiation In 1894, the German physidist, Max Plank, was working for a utility company to maximize visible light output from incandescent lamps using minimum power. Based on theoretical considerations, Planck postulated that electromagnetic energy could only be emitted at discrete values, rather than the continuum of predicted by classical physics, as multiples of the frequency of the radiation. Planck's Postulate took the mathematical form: E·hv where the energy emitted, in Joules, is the product of a constant, h, known as Planck's Constant, and the frequency of the radiation, v. Planck's Postulate was experimentally verified and h found to have the value of 6.626 x 1034 Js(Joule seconds). The idea that electromagnetic radiation energy had specific frequency dependent energy was termed a "quantum of action," a distressing finding for the dlassically trained Planck. Despite his objections, Planck adopted this quantization of energy as a last resort to reconcile experiment with theory. This discovery set the stage for the early understanding of atomic structure, led to the term "photon" to describe the packet of energy carried by light waves, led to an understanding of the photoelectric effect, eventually leading to the development of general quantum theory Planck's Relationship, in combination with the tight equation, c the energy of a photon from frequency or wavelength. λ w, allow expressions to be written to calculate ACTIVITY 4: QUANTIZATION OF THE ENERGY OF RADIATION To practice cakculations with Planck's Relationship, complete the following table, showing work with units in the right mest column, Convert given frequency to energy or given wavelength to energy. Take the value for Planck's Constant, h, to be 6.626 x 10"Js, show a calculation string include dimensions, reporting the final value to the proper number of significant figures Spectral Region Wavelength Frequency Energy in J/photon Show Calculation String λ in meters v in s or cps X-ray 6.0 x 10"m Blue light 4.5 x 10m Infrared 4.1 x 10" cps Microwave 7.3 x 101 cps Radio Wave 3.0x 10 m IV. Bohr's Quantum Model for the Hydrogen Atom Ernest Rutherford's Gold Foil Experiment of 1911 demonstrated the nuclear structure of the atom. Questions remained as to how electrons were arranged in the atom. The most common belief called for the negatively charged the late 19h century recognized a particle (an electron) traveling around a body (the positively charged nucleus) would continuously radiate energy, slowing over time, eventually falling into the nucleus. Matter would collapse. Page 8 of 12

provided to determine AH rxn for the following reaction: urf (klimol) CH4(g) + 3 Cl2(g) → CHCI3() + 3 HCI(g) airrxn-? A)-151 kJ B)33SkJ C) +662kJ D) +117kJ E)-217 kJ A) 4.1 atm B) 5.0 atm c) 6.4 atm D)1.1 atm E) 2.3 atm kg) of the copper sample if the specific heat capacity of copper is 0 CH4(g) 75 CHCI3() -134 HCI(g) -92 8) What pressure will 14.0 g of CO exert in a 3.5 L container at 75 C? 9) A sample of copper absorbs 43.6 kJ of heat, resulting in a temperature rise of 50.0°C, determine the mass (in .385 J/g C A) 226 kg B) 0.235 kg C)6.64 kg D) 119kg E)5.10 kg 10) Which of the following processes is exothermic? A) the ionization of a melting snow atom B) the breaking of a boiling of water bond C) the boiling of water D) the condensation of water E) All of the above processes are exothermic 11) Calculate the energy of the red light emitted by a neon atom with a wavelength of 703.2 nm. B)4.27 x 10-19J C) 2.34 x 10-19J D)6.45 x 10-19J E) 2.83 x 10-19J A)3.54 × 10-19J 12) Identify the color of a flame test for potassium D) yellow A) violet B) red C) white E) blue 13) Which of the following statements is TRUE? A) The emission spectrum of a particular element is always the same and can be used to identify the element. B) Part of the Bohr model proposed that electrons in the hydrogen atom are located in "stationary states" or particular orbits around the nucleus. C) The uncertainty principle states that we can never know both the exact location and speed of an electron. D) An orbital is the volume in which we are most likely to find an electron. E) All of the above are true. 14) Calculate the wavelength of an electron (m-9.11 x 10-28 g) moving at 3.66 × 106 m/s. A)1.99 x 10-10m B)5.03 x 10-10 m C) 1.81×10-10 m D)5.52 × 10-9 m E) 2.76 × 10-9 m 15) Which of the following quantum numbers describes the shape of an orbital? A) principal quantum number B) magnetic quantum number C) spin quantum number D) Schrödinger quantum number E) angular momentum quantum number 16) Determine the energy change associated with the transition from n = 2 to n-5 in the hydrogen atom. A)-218×10-19J B)+654 × 10-19 J C) +4.58 x 10-19 J D)-1.53 x 10-19 J E) +3.76 × 10-19J 17) If two electrons in the same atom have the same value of I, they are A) in the same sublevel, but not necessarily in the same level. me level, but different sublevel. C) in the same orbital. D) in different levels and in different shaped orbitals. E) none of the above.