Chapter 11
Electromagnetic Radiation: is a term used to describe all the different kinds of energies released into space by stars such as the Sun.
This link describes the electromagnetic spectrum and defines electromagnetic radiation.
Emissions by atoms:when atoms receive energy from some source-they become excited-they can release this energy by emitting light. The emitted energy is carried away by a photon.
www.youtube.com/watch?v=8TJ2GlWSPxI
Difference between continuous vs. discrete energy level:
Discrete energy level: only certain energy states are allowed. This means that the hydrogen atom must have certain discrete energy levels. All hydrogen atoms have the same set of discrete energy level.
Continuous energy level: any energy value is allowed
Difference: illustrated by comparing a flight of stairs with a ramp
www.youtube.com/watch?v=8TJ2GlWSPxI
Difference between continuous vs. discrete energy level:
Discrete energy level: only certain energy states are allowed. This means that the hydrogen atom must have certain discrete energy levels. All hydrogen atoms have the same set of discrete energy level.
Continuous energy level: any energy value is allowed
Difference: illustrated by comparing a flight of stairs with a ramp
Wave mechanical model of the atom:
A model created by Louis Victor de Brogile and Erwin Schrodinger that describes the electron in the hydrogen atom/
OBJECTIVE: To understand how the electron’s position is represented in the wave mechanical model.
By the mid-1920s it had become apparent that the Bohr model was incorrect. Scientists needed to pursue a totally new approach. Two young physicists, Louis Victor de Broglie from France and Erwin Schrödinger from Austria, suggested that because light seems to have both wave and particle characteristics (it behaves simultaneously as a wave and as a stream of particles), the electron might also exhibit both of these characteristics.
When Schrödinger carried out a mathematical analysis based on this idea, he found that it led to a new model for the hydrogen atom that seemed to apply equally well to other atoms—something Bohr’s model failed to do. We will now explore a general picture of this model, which is called the wave mechanical model of the atom.
In the Bohr model, the electron was assumed to move in circular orbits. In the wave mechanical model, on the other hand, the electron states are described by orbitals. Orbitals are nothing like orbits. To approximate the idea of an orbital, picture a single male firefly in a room in the center of which an open vial of female sex-attractant hormones is suspended. The room is extremely dark and there is a camera in one corner with its shutter open. Every time the firefly “flashes,” the camera records a pinpoint of light and thus the firefly’s position in the room at that moment. The firefly senses the sex at- tractant, and as you can imagine, it spends a lot of time at or close to it. How- ever, now and then the insect flies randomly around the room.
When the film is taken out of the camera and developed, the picture will probably look like Figure 11.18. Because a picture is brightest where the film has been exposed to the most light, the color intensity at any given point tells us how often the firefly visited a given point in the room. Notice that, as we might expect, the firefly spent the most time near the room’s center.
According to the wave mechanical model, the electron in the hydrogen atom can be pictured as being something like this firefly. Schrödinger found that he could not precisely describe the electron’s path. His mathematics enabled him only to predict the probabilities of finding the electron at given points in space around the nucleus. In its ground state the hydrogen electron has a probability map like that shown in Figure 11.19. The more intense the color at a particular point, the more probable that the electron will be found at that point at a given instant. The model gives no information about when the electron occupies a certain point in space or how it moves. In fact, we have good reasons to believe that we can never know the details of electron motion, no matter how sophisticated our models may become. But one thing we feel confident about is that the electron does not orbit the nucleus in circles as Bohr suggested.
A model created by Louis Victor de Brogile and Erwin Schrodinger that describes the electron in the hydrogen atom/
OBJECTIVE: To understand how the electron’s position is represented in the wave mechanical model.
By the mid-1920s it had become apparent that the Bohr model was incorrect. Scientists needed to pursue a totally new approach. Two young physicists, Louis Victor de Broglie from France and Erwin Schrödinger from Austria, suggested that because light seems to have both wave and particle characteristics (it behaves simultaneously as a wave and as a stream of particles), the electron might also exhibit both of these characteristics.
When Schrödinger carried out a mathematical analysis based on this idea, he found that it led to a new model for the hydrogen atom that seemed to apply equally well to other atoms—something Bohr’s model failed to do. We will now explore a general picture of this model, which is called the wave mechanical model of the atom.
In the Bohr model, the electron was assumed to move in circular orbits. In the wave mechanical model, on the other hand, the electron states are described by orbitals. Orbitals are nothing like orbits. To approximate the idea of an orbital, picture a single male firefly in a room in the center of which an open vial of female sex-attractant hormones is suspended. The room is extremely dark and there is a camera in one corner with its shutter open. Every time the firefly “flashes,” the camera records a pinpoint of light and thus the firefly’s position in the room at that moment. The firefly senses the sex at- tractant, and as you can imagine, it spends a lot of time at or close to it. How- ever, now and then the insect flies randomly around the room.
When the film is taken out of the camera and developed, the picture will probably look like Figure 11.18. Because a picture is brightest where the film has been exposed to the most light, the color intensity at any given point tells us how often the firefly visited a given point in the room. Notice that, as we might expect, the firefly spent the most time near the room’s center.
According to the wave mechanical model, the electron in the hydrogen atom can be pictured as being something like this firefly. Schrödinger found that he could not precisely describe the electron’s path. His mathematics enabled him only to predict the probabilities of finding the electron at given points in space around the nucleus. In its ground state the hydrogen electron has a probability map like that shown in Figure 11.19. The more intense the color at a particular point, the more probable that the electron will be found at that point at a given instant. The model gives no information about when the electron occupies a certain point in space or how it moves. In fact, we have good reasons to believe that we can never know the details of electron motion, no matter how sophisticated our models may become. But one thing we feel confident about is that the electron does not orbit the nucleus in circles as Bohr suggested.
Different types of Molecular Orbitals:
The Molecular Orbital Theory, initially developed by Robert S. Mullikan, incorporates the wave like characteristics of electrons in describing bonding behavior. In Molecular Orbital Theory, the bonding between atoms is described as a combination of their atomic orbitals. While theValence Bond Theory and Lewis Structures sufficiently explain simple models, the Molecular Orbital Theory provides answers to more complex questions. In the Molecular Orbital Theory, the electrons are delocalized. Electrons are considered delocalized when they are not assigned to a particular atom or bond (as in the case with Lewis Structures). Instead, the electrons are “smeared out” across the molecule. The Molecular Orbital Theory allows one to predict the distribution of electrons in a molecule which in turn can help predict molecular properties such as shape, magnetism, and Bond Order.
Atoms form bonds by sharing electrons. Atoms can share two, four, or six electrons, forming single, double, and triple bonds respectively. Although it is impossible to determine the exact position of an electron, it is possible to calculate the probability that one will find the electron at any point around the nucleus using the Schrödinger Equation. This equation can help predict and determine the energy and spatial distribution of the electron, as well as the shape of each orbital. The figure below shows the first five solutions to the equation in a three dimensional space. The colors show the phase of the function. In this diagram, blue stands for negative and red stands for positive. Note, however, that the 2s orbital has 2 phases, one of which is not visible because it is inside the other.
The Molecular Orbital Theory, initially developed by Robert S. Mullikan, incorporates the wave like characteristics of electrons in describing bonding behavior. In Molecular Orbital Theory, the bonding between atoms is described as a combination of their atomic orbitals. While theValence Bond Theory and Lewis Structures sufficiently explain simple models, the Molecular Orbital Theory provides answers to more complex questions. In the Molecular Orbital Theory, the electrons are delocalized. Electrons are considered delocalized when they are not assigned to a particular atom or bond (as in the case with Lewis Structures). Instead, the electrons are “smeared out” across the molecule. The Molecular Orbital Theory allows one to predict the distribution of electrons in a molecule which in turn can help predict molecular properties such as shape, magnetism, and Bond Order.
Atoms form bonds by sharing electrons. Atoms can share two, four, or six electrons, forming single, double, and triple bonds respectively. Although it is impossible to determine the exact position of an electron, it is possible to calculate the probability that one will find the electron at any point around the nucleus using the Schrödinger Equation. This equation can help predict and determine the energy and spatial distribution of the electron, as well as the shape of each orbital. The figure below shows the first five solutions to the equation in a three dimensional space. The colors show the phase of the function. In this diagram, blue stands for negative and red stands for positive. Note, however, that the 2s orbital has 2 phases, one of which is not visible because it is inside the other.
This link gives you more information about the molecular orbital theory.
The Pauli Exclusion Principle
The Pauli Exclusion Principle states that, in an atom, no two electrons can have the same four electronic quantum numbers. We are aware that in one orbital a maximum of two electrons can be found and the two electrons must have opposing spins. That means one would spin up ( +1/2) and the other would spin down (-1/2).
This website gives additional information about the Pauli Exclusion Principle and defines it.
Electron Configuration: the representation of the arrangement of electrons that are distributed among the orbital shells and subshells
Examples:
This activity gives you more information about the electron configuration.
This website goes more in depth about electron configuration.
This additional website gives you even more information about electron configuration