CHE 101 Lecture Notes - Lecture 6: Niels Bohr, Atomic Nucleus, Photographic Film

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11 Jun 2018

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The Electronic Structure of the Atom

When a hydrogen atom is irradiated with energy, some of the energy is absorbed and then re-

remitted. If the light emitted by hydrogen atoms is passed through a prism and then onto a

strip of photographic film, the line spectrum.

In 1913 Niels Bohr proposed a model which explained why the hydrogen atom’s line

spectrum looks like it does and why only certain energies are observed in the spectrum. He

proposed that the electron in a hydrogen atom only exists in specific energy states. These

energy states are associated with specific circular orbits which the electron can occupy

around the atom. When an electron absorbs or emits a specific amount of energy is

instantaneously moves from one orbit to another; the greater the energy the father the orbit

from the atomic nucleus.

The pattern of lines in the spectrum reflects the energy level pattern. The observed spectrum

represents energy level differences occurring when an electron in a higher energy level gives

off energy and drops down to a lower level. The energy difference between two particular

energy levels is called the quantum of energy associated with the transition between the two

levels.

A few years after Bohr published his theories on electron orbits, several significant changes

were made to his basic ideas. The theory of quantum mechanics which finally emerged is

beyond the scope of this course, but one change in Bohr’s theory must be mentioned. The

notion of electrons orbiting a nucleus along a specific path in a well defined orbit had to be

abandoned and replaced by the idea that different electrons, depending on their energies,

simply occupy particular regions of space called orbitals.

Experimental studies show that the lowest set of energy levels for hydrogen is arranged as

followed. Each dash represents the energy possessed by a particular orbital in the atom. The

letters s, p, d and f refer to four different types of orbitals which are discussed later.

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Document Summary

When a hydrogen atom is irradiated with energy, some of the energy is absorbed and then re- remitted. If the light emitted by hydrogen atoms is passed through a prism and then onto a strip of photographic film, the line spectrum. In 1913 niels bohr proposed a model which explained why the hydrogen atom"s line spectrum looks like it does and why only certain energies are observed in the spectrum. He proposed that the electron in a hydrogen atom only exists in specific energy states. These energy states are associated with specific circular orbits which the electron can occupy around the atom. When an electron absorbs or emits a specific amount of energy is instantaneously moves from one orbit to another; the greater the energy the father the orbit from the atomic nucleus. The pattern of lines in the spectrum reflects the energy level pattern.

Related Questions

Use a ruler to calibrate the spectral limits in the figure above. In other words, what are the right and left limits in nm, and what is the equation that converts distance on this page in cm to spectral units of nm? This âcalibrationâ will help you with the next item.

Use the NIST Atomic Spectral Database to assign the three bright spectral lines in the hydrogen spectrum.

Abstract This physical chemistry laboratory exercise will have students work with provided emission spectra for several elements and data collected on the NIST Atomic Spectral Database. First, students will develop a method for calculating what wavelengths of visible light are associated with the most intense spectral lines in the provided visible emission spectra. Then, the NIST Atomic Spectral Database will be accessed in order to identify select properties associated with the four most intense spectral lines. Introduction The emission process can be described in two general parts. Initially, energy is absorbed by an atom, and its electrons can be moved into higher energy (excited) states from their ground state The excitedrelectrons then "relax" and drop back to their ground state. Energy lost during an electron's retaxation process is emitted as a photon. Recall that the energy of a photon is photon upper E lower Where Ephoton is the energy of the photon that is emitted when the emitter drops from an upper energy state to a lower energy state, h is Planck's constant, c is the speed of light, and v is the wavenumber. Remember that the length units should match for c and v This is a good time to revisit a few concepts. Atoms and molecules possess discrete energy levels their energy levels are quantized and not continuous. Using eq 7.1, it is possible to determine the energy associated with a specific excited state to ground state transition if we can determine the wavelength of emitted light. Also keep in mind that there are selection rules that limit the type of transitions we can expect to observe. All of these points are reflected in an elemental or ionic emission spectrum. The visible light spectrum falls within a fairly narrow range of wavelengths, from approximately 400 to 700 nm. Even so, discrete spectral lines are seen in each element's visible light emission spectrum. Each (take some time to reflect on why that would be), each element also has a unique emission spectrum. This provides a diagnostic tool for determining the composition of a sample. As an example, the elements present in celestial objects can be determined by the light that they produce line represents one possible transition. Since each element has unique energy levels Some of the transitions observed in this lab exercise involve d-orbitals. As such, a discussion regarding d-orbitals and related selection rules is necessary at this point. The first goal is to determine which character table should be used. Start by observing the shape and relative orientations of the d-orbitals. Refer to Figure 1 below

Use the NIST Atomic Spectral Database to assign the four brightest spectral lines for Li and He. In a table, list the transition wavelength, lower and upper state electron configurations, the lower and upper state term symbols, the lower and upper state J 71 values, and the lower and upper state degeneracies (http://physics.nist.gov/PhysRefData/ASD/lines_form.html). Hint, use a minimum Aki value to reduce the number of lines reported by the NIST search.

provided to determine AH rxn for the following reaction: urf (klimol) CH4(g) + 3 Cl2(g) â 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 50.0Â°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 Ã 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 Ã 106 m/s. A)1.99 x 10-10m B)5.03 x 10-10 m C) 1.81Ã10-10 m D)5.52 Ã 10-9 m E) 2.76 Ã 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) SchrÃ¶dinger 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)-218Ã10-19J B)+654 Ã 10-19 J C) +4.58 x 10-19 J D)-1.53 x 10-19 J E) +3.76 Ã 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.

CHE 101 Lecture Notes - Lecture 6: Niels Bohr, Atomic Nucleus, Photographic Film

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