The Bohr model of the atom, developed in the early twentieth century, was an attempt to explain patterns in way atoms and electrons absorb, retain, and release energy. The model assumed an atom's structure resembles the solar system with the atomic nucleus at the center and electrons moving in circular orbits similar planet orbiting the Sun. The Bohr model represented an advancement in the understanding of atomic structure and contributed to the development of quantum mechanics. Show
Above is a Bohr Atom. Click on the grey rings to move the electron from orbital to orbital. Change the number of excitation states the electron has with the slider at the lower left and click on the hidden, visible and comment buttons to toggle information about the atom on and off. It is essential to understand that the planet-like imagery is just a representation. The planetary model is not consistent with our current knowledge of the structure of the atom. However, the Bohr atom remains a popular teaching tool because it illustrates the relationship between energy, electron position, and the emission of electromagnetic energy.. Development of the Bohr model of the atom helped establish a framework for understanding how electrons absorb and release discrete amounts (quanta) of energy by indicating that electrons associated with an atom do not have free range to be anywhere around that atom. Instead, electrons maintain discrete positions around the nucleus. In the Bohr atom:
The lowest energy level an electron can occupy is called the ground state. Higher orbitals represent higher excitation states. The higher the excitation state, the more energy the electron contains. When an electron absorbs energy, it jumps to a higher orbital. This is called an excited state. An electron in an excited state can release energy and 'fall' to a lower state. When it does, the electron releases a photon of electromagnetic energy. The energy contained in that photon corresponds to the difference between the two states the electron moves between. When the electron returns to the ground state, it can no longer release energy but can absorb quanta of energy and move up to excitation states (higher orbitals). The number of movements an electron can make depends on the number of excitation states available. In the case of one ground state plus one excitation state, there is only one possible state change. The electron can absorb one quantum of energy and jump up to the excitation state. From that excitation state, the electron can then drop back down, releasing a photon with a fixed amount of energy based on the energy lost by the electron when it fell to the lower orbital. The addition of a second excitation state increases the number of moves possible from one to three: from the ground state to excitation state 1, from the ground state to excitation state 2, and from excitation state 1 to excitation state 2. As the number of excitation states increases, the number of possible moves increases as an arithmetic series. With four excitation states, the number of state changes is 10, which is 4 plus 3 plus 2 plus 1. The Bohr representation of the atom also makes it possible to visualize movements of electrons from particular states. In an atom with six excitation states, an electron can jump from the ground state up to any one of those six states. An electron any of the excitation states can absorb energy and jump up to a higher state, or release a photon and fall to a lower state. It is important to remember that the Bohr atom is not an accurate representation of how atoms orbit the nucleus. However, this model helps illustration some basic concepts of energy absorption and release by atoms and their electrons. Check your understanding Video Overview Related Content Are you loving this? Not loving this? Please consider taking a moment to share your feedback with us. Thanks!
Students will again focus on the first 20 elements. Students will first look at a diagram and animation to understand the basic pattern of the arrangement of electrons on energy levels around an atom. Students will be given cards with information about the electrons and energy levels for each of the first 20 atoms. They will again try to correctly match the cards with each element. ObjectiveStudents will be able to interpret the information given in the periodic table to describe the arrangement of electrons on the energy levels around an atom. EvaluationDownload the student activity sheet, and distribute one per student when specified in the activity. The activity sheet will serve as the “Evaluate” component of each 5-E lesson plan. About this LessonBe sure that the 20 atom name cards are posted around the room. You will need the five cards on the right hand side of each sheet. This lesson is intended as a follow-up to chapter 4, lesson 2. For Lesson 4.3, students can play the Periodic Table Game, Game #2. This is an online version of the periodic table card game from this lesson that you can assign as class work or homework after students have played the game in the classroom.
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