The Bohr Model. In 1913, Niels Bohr ( ), a young Danish physicist and a student of Rutherford, developed a new atomic model.

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1 Chapter 5 Electrons In Atoms 5.1 Revising the Atomic Model 5.2 Electron Arrangement in Atoms 5.3 Atomic Emission Spectra and the Quantum Mechanical Model 1 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. Energy Levels in Atoms The Bohr Model In 1913, Niels Bohr ( ), a young Danish physicist and a student of Rutherford, developed a new atomic model. He changed Rutherford s model to incorporate newer discoveries about how the energy of an atom changes when the atom absorbs or emits light. 2 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

2 Energy Levels in Atoms The Bohr Model Bohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus. 3 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. Energy Levels in Atoms The Bohr Model Each possible electron orbit in Bohr s model has a fixed energy. The fixed energies an electron can have are called energy levels. A quantum of energy is the amount of energy required to move an electron from one energy level to another energy level. 4 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

3 Energy Levels in Atoms The Bohr Model The rungs on this ladder are somewhat like the energy levels in Bohr s model of the atom. A person on a ladder cannot stand between the rungs. Similarly, the electrons in an atom cannot exist between energy levels. 5 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. Energy Levels in Atoms The Bohr Model The rungs on this ladder are somewhat like the energy levels in Bohr s model of the atom. The energy levels in atoms are unequally spaced, like the rungs in this unusual ladder. The higher energy levels are closer together. 6 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

4 How does the Bohr model improve upon the Rutherford model? The Rutherford model could not explain why elements that have been heated to higher and higher temperatures give off different colors of light. The Bohr model explains how the energy levels of electrons in an atom change when the atom emits light. 7 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. The Quantum Mechanical Model The Quantum Mechanical Model What does the quantum mechanical model determine about the electrons in an atom? 8 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

5 The Quantum Mechanical Model Austrian physicist Erwin Schrödinger ( ) used new theoretical calculations and experimental results to devise and solve a mathematical equation describing the behavior of the electron in a hydrogen atom. The modern description of the electrons in atoms, the quantum mechanical model, came from the mathematical solutions to the Schrödinger equation. 9 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. The Quantum Mechanical Model Like the Bohr model, the quantum mechanical model of the atom restricts the energy of electrons to certain values. Unlike the Bohr model, however, the quantum mechanical model does not specify an exact path the electron takes around the nucleus. 10 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

6 The Quantum Mechanical Model The quantum mechanical model determines the allowed energies an electron can have and how likely it is to find the electron in various locations around the nucleus of an atom. 11 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. The Quantum Mechanical Model Probability describes how likely it is to find an electron in a particular location around the nucleus of an atom. 12 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

7 The Quantum Mechanical Model In the quantum mechanical model, the probability of finding an electron within a certain volume of space surrounding the nucleus can be represented as a fuzzy cloudlike region. The cloud is more dense where the probability of finding the electron is high. Electron cloud 13 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. How are the quantum mechanical model and the Bohr model alike? How are they different? Like the Bohr model, the quantum mechanical model restricts the energy of electrons to certain values. Unlike the Bohr model, the quantum mechanical model does not specify an exact path the electron takes around the nucleus. 14 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

8 How do sublevels of principal energy levels differ? 15 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. For each energy level, the Schrödinger equation also leads to a mathematical expression, called an atomic orbital. An atomic orbital is represented pictorially as a region of space in which there is a high probability of finding an electron. 16 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

9 The energy levels of electrons in the quantum mechanical model are labeled by principal quantum numbers (n). These numbers are assigned the values n = 1, 2, 3, 4, and so forth. For each principal energy level greater than 1, there are several orbitals with different shapes and at different energy levels. 17 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. The energy levels of electrons in the quantum mechanical model are labeled by principal quantum numbers (n). These numbers are assigned the values n = 1, 2, 3, 4, and so forth. For each principal energy level greater than 1, there are several orbitals with different shapes and at different energy levels. These energy levels within a principal energy level constitute energy sublevels. 18 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

10 Each energy sublevel corresponds to one or more orbitals of different shapes. The orbitals describe where an electron is likely to be found. 19 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. For a given principal energy level greater than 1, there is one s orbital, 3 p orbitals, and 5 d orbitals. 20 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

11 The numbers and types of atomic orbitals depend on the principal energy level. Summary of Principal Energy Levels and Sublevels Principal energy level Number of sublevels Type of sublevel Maximum number of electrons n = 1 1 1s (1 orbital) 2 n = 2 2 2s (1 orbital), 2p (3 orbitals) 8 n = 3 3 n = 4 4 3s (1 orbital), 3p (3 orbitals), 3d (5 orbitals) 4s (1 orbital), 4p (3 orbitals), 4d (5 orbitals), 4f (7 orbitals) Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. CHEMISTRY & YOU Why do scientists no longer use physical models to describe the motion of electrons? Previous models of the atom were physical models based on the motion of large objects. Theoretical calculations and experimental results showed that these models did not always correctly describe electron motion. Schrödinger devised a mathematical equation describing the behavior of the electron in a hydrogen atom. The quantum mechanical model came from the solutions to the Schrödinger equation. 22 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

12 Key Concepts Bohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus. The quantum mechanical model determines the allowed energies an electron can have and how likely it is to find the electron in various locations around the nucleus of an atom. Each energy sublevel corresponds to one or more orbitals of different shapes, which describe where the electron is likely to be found. 23 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. Glossary Terms energy level: the specific energies an electron in an atom or other system can have quantum: the amount of energy needed to move an electron from one energy level to another 24 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

13 Glossary Terms quantum mechanical model: the modern description, primarily mathematical, of the behavior of electrons in atoms atomic orbital: a mathematical expression describing the probability of finding an electron at various locations; usually represented by the region of space around the nucleus where there is a high probability of finding an electron 25 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved. END OF Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.