Electron Structure

Electron Structure - ELECTRON STRUCTURE I Experimental...

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1 ELECTRON STRUCTURE I. Experimental Approach A. Periodic Law. 1. The physical and chemical properties of elements are periodic functions of their atomic numbers. Since the atomic numbers are equal to the number of electrons in a neutral atom, the properties are functions of the number of electrons. a. Group 17 (Halogens): 1) Reactive nonmetals. 2) Form -1 ions. 3) Exist as diatomic molecules in their elemental forms (F 2 , Cl 2 , etc.) b. Group 18 (Inert Gases): 1) Unreactive monatomic gases. 2) No compounds are known for the lighter elements (He and Ne). 3) Heavier members, such as Xe, form compounds only with strong nonmetals such as O and F. c. Group 1 (Alkali Metals): 1) Soft, reactive metals. 2) Form +1 ions. 2. Chemical and physical properties (except for mass) are due to electron structure. Those elements with similar properties, that is, that are in the same Group in the Periodic Table, must have similar electron structures. B. Emission Spectra of elements. 1. Line vs. continuous spectra. a. Spectrum 1) When electromagnetic radiation (light) passes through a prism or impinges on a grating, the light is separated into its different wavelengths (colors), 2) The spectrum is the display of the radiation after it has been separated into its component wave lengths. (Plural = spectra) b White light gives a continuous spectrum . That is, one that contains all wave lengths (colors) merging into one another. c. A line spectrum contains only several discrete wavelengths. 2. Light obtained from energized atoms exhibits a line spectrum. Lines are independent of the particular isotope of the element. Therefore, line spectra are functions of the electron structures of atoms.
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2 C. Consideration of Light. Transmission of energy through space. Two ways that energy can be transferred, through wave disturbance that is propagated through space or by a particle that moves through space. 1. Light as a Wave Phenomenon. a. Radiant energy (light) - an oscillating electric and magnetic field (force) that is propagated through free space at a speed of 2.9979x10 8 m/s. b. Some wave properties. At some instant in time, the wave resembles a series of crests and valleys that are evenly spaced. Distance +A –A 0 λ λ λ λ λ c. Some parameters that describe a wave. 1) Wavelength ( λ ) - distance between repeating units of the wave. This can be expressed in any convenient unit of length. The SI unit is the meter . 2) Amplitude (A) - value of the wave disturbance. Light is an oscillating electric and magnetic field, therefore, the amplitude is the field strength. Since the field is a vector quantity, it can be positive or negative. The intensity of the radiation is directly proportional to A 2 . 3) Frequency ( ν ) - Number of cycles per second. The wave packet moves through space at its speed of propagation ( C ). Therefore, if one were to monitor the field at one point over a period of time, it would appear as if the field was going through a series of complete cycles as the wave passed the point. The number of complete cycles per second that one would observe is the frequency.
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