5.1 Revising the Atomic Model > 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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

5.1 Revising the Atomic Model > 2 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Shown here is a life- sized model of a skier, but not all models are physical. In fact, the current model of the atom is a mathematical model. CHEMISTRY & YOU Why do scientists use mathematical models to describe the position of electrons in atoms?

5.1 Revising the Atomic Model > 3 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Energy Levels in Atoms It explained only a few simple properties of atoms. Limitations of Rutherford’s Atomic Model

5.1 Revising the Atomic Model > 4 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Energy Levels in Atoms Limitations of Rutherford’s Atomic Model It explained only a few simple properties of atoms. It could not explain all the chemical properties of elements.

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Energy Levels in Atoms It explained only a few simple properties of atoms. It could not explain all the chemical properties of elements. For example, Rutherford’s model could not explain why an object such as the iron scroll shown here first glows dull red, then yellow, and then white when heated to higher and higher temperatures. Limitations of Rutherford’s Atomic Model

5.1 Revising the Atomic Model > 6 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. What did Bohr propose in his model of the atom? Energy Levels in Atoms

5.1 Revising the Atomic Model > 7 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Energy Levels in Atoms Bohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus. The Bohr Model

5.1 Revising the Atomic Model > 8 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Energy Levels in Atoms In 1913, Niels Bohr (1885 – 1962), 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 energy. The Bohr Model

5.1 Revising the Atomic Model > 9 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Each possible electron orbit in Bohr’s model has a fixed energy. Energy Levels in Atoms The Bohr Model

5.1 Revising the Atomic Model > 10 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Each possible electron orbit in Bohr’s model has a fixed energy. Energy Levels in Atoms The fixed energies an electron can have are called energy levels. The Bohr Model

5.1 Revising the Atomic Model > 11 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Each possible electron orbit in Bohr’s model has a fixed energy. Energy Levels in Atoms 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. The Bohr Model

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Energy Levels in Atoms 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. The Bohr Model

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Energy Levels in Atoms The rungs on this ladder are somewhat like the energy levels in Bohr’s model of the atom. The Bohr Model The energy levels in atoms are unequally spaced. The higher energy levels are closer together.

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Energy Levels in Atoms The rungs on this ladder are somewhat like the energy levels in Bohr’s model of the atom. The Bohr Model Quantum Jump, when an electron moves from one energy level to another. The light given off is called a photon. Different colors are visible based on the number of levels changed.

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. How does the Bohr model improve upon the Rutherford model?

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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.

5.1 Revising the Atomic Model > 17 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. What does the quantum mechanical model determine about the electrons in an atom? The Quantum Mechanical Model

5.1 Revising the Atomic Model > 18 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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. The Quantum Mechanical Model

5.1 Revising the Atomic Model > 19 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Austrian physicist Erwin Schrödinger (1887– 1961) 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. The Quantum Mechanical Model

5.1 Revising the Atomic Model > 20 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.

5.1 Revising the Atomic Model > 21 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Probability describes how likely it is to find an electron in a particular location around the nucleus of an atom. The Quantum Mechanical Model

5.1 Revising the Atomic Model > 22 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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. The Quantum Mechanical Model Electron cloud

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?

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.

5.1 Revising the Atomic Model > 25 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Orbitals How do sublevels of principal energy levels differ?

5.1 Revising the Atomic Model > 26 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Each energy sublevel corresponds to one or more orbitals of different shapes. The orbitals describe where an electron is likely to be found. Atomic Orbitals

5.1 Revising the Atomic Model > 27 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Orbitals Solutions to the Schrödinger equation give the energies, or energy levels, an electron can have.

5.1 Revising the Atomic Model > 28 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Orbitals Solutions to the Schrödinger equation give the energies, or energy levels, an electron can have. For each energy level, the Schrödinger equation also leads to a mathematical expression, called an atomic orbital.

5.1 Revising the Atomic Model > 29 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Orbitals Solutions to the Schrödinger equation give the energies, or energy levels, an electron can have. 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.

5.1 Revising the Atomic Model > 30 Atomic Orbitals Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Energy Levels are like floors and obitals are like rooms on each floor.

5.1 Revising the Atomic Model > 31 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Orbitals The energy levels of electrons in the quantum mechanical model are labeled by principal quantum numbers (n).

5.1 Revising the Atomic Model > 32 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Orbitals 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.

5.1 Revising the Atomic Model > 33 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Orbitals 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.

5.1 Revising the Atomic Model > 34 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Orbitals 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.

5.1 Revising the Atomic Model > 35 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Orbitals The s orbitals are spherical. Different atomic orbitals are denoted by letters.

5.1 Revising the Atomic Model > 36 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Orbitals The s orbitals are spherical. The p orbitals are dumbbell-shaped. Different atomic orbitals are denoted by letters.

5.1 Revising the Atomic Model > 37 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Orbitals The s orbitals are spherical. The p orbitals are dumbbell-shaped. The d orbitals are double dumbbell-shaped. Different atomic orbitals are denoted by letters.

5.1 Revising the Atomic Model > 38 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Orbitals For a given principal energy level greater than 1, there is one s orbital…

5.1 Revising the Atomic Model > 39 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Orbitals For a given principal energy level greater than 1, there is one s orbital… 3 p orbitals...

5.1 Revising the Atomic Model > 40 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Orbitals For a given principal energy level greater than 1, there is one s orbital… 3 p orbitals… and 5 d orbitals.

5.1 Revising the Atomic Model > 41 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Orbitals Four of the five d orbitals have the same shape but different orientations in space.

5.1 Revising the Atomic Model > 42 Atomic Orbitals Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Why is the atom pictured as a round sphere when only one orbital is round?

5.1 Revising the Atomic Model > 43 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Orbitals Summary of Principal Energy Levels and Sublevels Principal energy level Number of sublevels Type of sublevel Maximum number of electrons n = 111s (1 orbital)2 n = 222s (1 orbital), 2p (3 orbitals)8 n = 33 3s (1 orbital), 3p (3 orbitals), 3d (5 orbitals) 18 n = 44 4s (1 orbital), 4p (3 orbitals), 4d (5 orbitals), 4f (7 orbitals) 32 The numbers and types of atomic orbitals depend on the principal energy level.

5.1 Revising the Atomic Model > 44 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Orbitals The principal quantum number, n, always equals the number of sublevels within that principal energy level.

5.1 Revising the Atomic Model > 45 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Orbitals The principal quantum number, n, always equals the number of sublevels within that principal energy level. The number of orbitals in a principal energy level is equal to n 2.

5.1 Revising the Atomic Model > 46 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Orbitals The principal quantum number, n, always equals the number of sublevels within that principal energy level. The number of orbitals in a principal energy level is equal to n 2. A maximum of two electrons can occupy an orbital.

5.1 Revising the Atomic Model > 47 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Atomic Orbitals The principal quantum number, n, always equals the number of sublevels within that principal energy level. The number of orbitals in a principal energy level is equal to n 2. A maximum of two electrons can occupy an orbital. Therefore, the maximum number of electrons that can occupy a principal energy level is given by the formula 2n 2.

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Calculate the maximum number of electrons in the 5 th principal energy level (n = 5).

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Calculate the maximum number of electrons in the 5 th principal energy level (n = 5). The maximum number of electrons that can occupy a principal energy level is given by the formula 2n 2. If n = 5, 2n 2 = 50.

5.1 Revising the Atomic Model > 50 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Why do scientists no longer use physical models to describe the motion of electrons?

5.1 Revising the Atomic Model > 51 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Previous models of the atom were physical models based on the motion of large objects. Why do scientists no longer use physical models to describe the motion of electrons?

5.1 Revising the Atomic Model > 52 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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. Why do scientists no longer use physical models to describe the motion of electrons?

5.1 Revising the Atomic Model > 53 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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. Why do scientists no longer use physical models to describe the motion of electrons?

5.1 Revising the Atomic Model > 54 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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.

5.1 Revising the Atomic Model > 55 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. END OF 5.1