Stage+2+Physics+Unit+4 - 1 Stage II Physics Atoms and...

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1 Stage II Physics Atoms and Nuclei
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2 Section 4: Atoms and Nuclei Topic 1: The Structure of the Atom The existence of line emission spectra from atomic gases is used to infer a structure of an atom in terms of states with discrete energies. The structure of an atom as a positive nucleus surrounded by one or more electrons is assumed. The visible continuous spectra emitted by hot objects are introduced and atomic absorption spectra are explained. The phenomena of population inversion and stimulated emission are used to introduce a simple explanation of the operation of a laser. Key Ideas Students should know and understand the following: Intended Student Learning Students should be able to do the following: Line Emission Spectrum A hot vapour of a pure element emits light of discrete frequencies, resulting in a line emission spectrum when the light is viewed with a spectrometer. Describe the general characteristics of the line emission spectra of elements. Explain how the uniqueness of the spectra of elements can be used to identify the presence of an element. Energy Levels in Atoms The presence of discrete frequencies in the spectra of atoms is evidence for the existence of different states in atoms. The states have their own specific energies. The different energies can be represented on an energy-level diagram. When an electron makes a transition from a higher-energy state to a lower-energy state in an atom, the energy of the atom decreases and can be released as a photon. The energy of the emitted photon is given by n m n m E E hf E E , where is the energy difference of the atom, hf is the energy of the photon, and f is the frequency of the emitted light. Explain how the presence of discrete frequencies in line emission spectra provides evidence for the existence of states with discrete energies in atoms. Solve problems involving the use of n m E E hf . Draw energy-level diagrams to represent the energies of different states in an atom. Given an energy-level diagram, calculate the frequencies and wavelengths of lines corresponding to specified transitions. An atom is in its ground state when its electrons have their lowest energy. If an electron is in any of the higher-energy states, the atom is said to be in an excited state. Spectrum of Atomic Hydrogen
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3 Key Ideas Students should know and understand the following: Intended Student Learning Students should be able to do the following: The line emission spectrum of atomic hydrogen consists of several series of lines, each of which converges to a series limit. Draw, on an energy-level diagram of hydrogen, transitions corresponding to each of the series terminating at the three lowest-energy levels. Relate the magnitude of the transitions on an energy-level diagram to the region in the electromagnetic spectrum of the emitted photons (ultraviolet, visible, or infrared).
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