Transcript Section 2:
Section 2: The Quantum Model of the Atom! • In this section we will learn how to use the quantum-number code to describe the properties of electrons in atoms…. At the end of class today you should be able to : Define: a. main energy levels b. quantum numbers List the four quantum numbers. • What is your address… house/apartment number… zip code… the whole business. • These items describe the location of your residence. • In the same way that no two houses have the same address, no two electrons in an atom have the same set of four quantum numbers… So scientists – physicists mostly – are still puzzled about electrons. Why did hydrogen’s electron exist around the nucleus only in certain allowed orbits with definite energies? Why couldn’t it exist in a limitless number of orbits with slightly different energies? Enter Louis de Broglie This French scientist combined Einstein’s work with Planck’s math… and used Bohr’s model to propose some ideas that led to a revolution in understanding matter! De Broglie hypothesized that electrons have wavelike properties. • And after investigations and experiments, it is confirmed that electrons have dual waveparticle nature. • And this troubled scientists who wanted to know: Enter Werner Heisenberg Still about the same time, 1920s, a German theoretical physicist made a proposal about attempting to locate a specific electron. • Werner Heisenberg came up with the idea that, since little tiny things have both wave and particle properties, that you can’t know the position of the particle version and the energy of the wave version with any precision at the same time. • This idea is called the Heisenberg uncertainty principle. • It states that it is impossible to determine simultaneously both the position and velocity of an electron or any other particle. Orbitals indicate probable electron locations… Schrödinger To make the Bohr model way better, Erwin Schrödinger came up with an equation that fixed everything and made the world of the atom a way more awesome place. • Instead of the one variable, n, that Bohr used in his equation, he came up with a better equation where there were a bunch of other variables, too. And LOTS and LOTS of crazy math… beaucoup crazy math… Quantum numbers Scientists use Schrodinger’s wave equation to describe atomic orbitals accurately. Electrons don’t travel around the nucleus in neat orbits, as Bohr postulated. Instead, they exist in certain regions called orbitals. An orbital is a 3-dimensional region around the nucleus that indicated the probable location of an electron. To describe these orbitals accurately, we use quantum numbers. Orbitals have different shapes & sizes! • Quantum numbers specify the properties of atomic orbitals and the properties of electrons in orbitals. • They are numbers used to specify the energy, location, shape and orientation of atomic orbitals, as well as the spins of electrons in these orbitals. • There are four quantum numbers. And keep in mind that it is the SET of four quantum numbers that’s important. Principal quantum number Symbol: n Indicates: main energy level occupied by the electron A word about n Values of n are positive integers only: 1, 2, 3 and so on. It will ALWAYS be a whole number and NEVER less than one. As n increases, the electron’s energy and its average distance from the nucleus increase. See the next slide! You can draw this if you wish… Angular momentum quantum number Symbol: l “little l” Indicates: the shape of the orbital Values of l : 0, 1, 2, … n – 1 l will always be a whole number and will NEVER be as large as the “n” value it goes with. • Depending on the value of , an orbital is assigned a letter, s, p, d and f. Orbital letter designations orbital l=0 l=1 l=2 l=3 s p d f There can be more than one shape of orbital Within each energy level (‘n’). It just so happens that n = the variety of Shapes within each energy level. For example… n = 1 and only has 1 shape, s n = 2 and has 2 – s and p n = 3 and has s, p and d n = 4 and has s, p, d and f… You get the picture! We will primarily use elements with s, p and d shapes. s, p, and d orbital shapes I’ll show you f in a minute… it’s crazy! #3 - Magnetic quantum number Symbol: ml (that’s m sub-l) Indicates: the direction or orientation of an orbital around the nucleus. For example, it tells how the p orbital is positioned along x, y and z axes. The Quantum Model of the Atom Shapes and orientations of s, p, d and f orbitals #4 - Spin quantum number Symbol: m s Indicates: the direction the electrons are positioned (spin) in the orbital. Values: +1/2 and -1/2 One moves clockwise and the other moves counter clockwise Wanna play the dizzy electron game?!? I need two volunteers with good balance… • Only 2 electrons live in a single orbital but they MUST have opposite spin states. • Though it’s called the “spin quantum number”, electrons don’t actually spin. It’s more of a traditional thing to call it that and indicates a “state” in a magnetic field. Clarification time An orbital is a single allowed location for electrons. It is described by specific values of n, m and l. It can only hold 2 electrons. A sublevel includes all the similarly shaped orbitals in a particular main energy level. So for a given value of n, a sublevel consists of all orbitals with the same value of l. Textbook Pg. 104 Use this chart to fill in the table at the end of your notes! Target Practice! Show what cha know! Pg. 104 Review Q’s Answer Q’s 1 - 3 The Quantum Model of the Atom Chapter 4 Electrons Accommodated in Energy Levels and Sublevels Quantum Number And what that Quantum Number Means Principle Quantum Number “n” Tells the position or energy level that the electrons are traveling in. Whole numbers: 17. 1 is closest to the nucleus. Angular Momentum Number “l” Tells the shape of the orbital (s, p, d and f). Magnetic Quantum Number “ml” Tells the orientation (3D) in space of the orbital. Spin Quantum Number “ms” Tells the “spin” state of each of the 2 electrons( +1/2 or -1/2). Bellwork What is the name of the current atomic model? Name the 3 scientists whose work formed the orbitals and quantum numbers. Describe. What are the 4 quantum numbers? Describe. What is the maximum number of electrons in each orbital? Target Practice – turn in with your name, please! 1) List the 4 quantum numbers with a brief description of what they do. 2) Which is closer to the nucleus – n=3 or n=7? 3) How many orientations of p are there? How many orientations of d are there?