2. GPS Standards SC3a – Discriminate between the relative size, charge, and position of protons, neutrons, and electrons in the atom. Identify the inadequacies in the Rutherford atomic model. Identify the new proposal in the Bohr model of the atom. Describe the energies and positions of electrons according to the quantum mechanical model. Describe how the shapes of orbitals related to different sublevels differ.
3. Essential Question How are Rutherford’s, Bohr’s, and the quantum mechanical models related to each other?
4. Notes Inadequacies in Rutherford’s Model Could not explain why metals and metal compounds give off characteristic colors when heated in a flame Could not explain why heated metals glow red, then yellow, then white Could not explain the chemical properties of elements Treated the electron as a particle
5. The Bohr Model Revised Rutherford’s model to include information about how the energy of an atom changes when it absorbs or emits light Proposed that an electron is found only in specific circular paths, or orbits, around the nucleus Each proposed orbit has a fixed energy called an energy level Higher the energy of an electron, the farther it is from the nucleus Quantum – the amount of energy required to move an electron from one energy level to another energy level Gave results in agreement with experiments for the hydrogen atom Failed to explain the energies absorbed and emitted by atoms with more than one electron Treated the electron as a particle
6. Quantum Mechanical Model Schrodinger Devised a mathematical equation describing electron as a wave Quantum mechanical model modern description of the electrons around an atom based on mathematical solutions to Shrödinger’s equation Based on the probability of finding an electron within a particular volume of space around the nucleus By treating the electron as an electron wave instead of a particle, most of the problems associated with Bohr’s model were alleviated. There are still some problems that we will look at later. The model is still a work in progress.
7. September 7, 2011 Essential Question How are quantum numbers used to describe electrons?
8. Quantum Numbers Each electron around an atom has a set of 4 quantum numbers which describe the “energy address” of the electron. Principal quantum number (n) First quantum number Represents the energy level in which the electron is found (larger value of n = higher energy) Determines the size of an orbital (larger value of n = larger orbital size) The values of n are successive integers beginning with 1 (n = 1, 2, 3, 4, …., ) Each energy level represents 1 period on the periodic table. Maximum number of orbitals in an energy level = n2 Maximum number of electrons in an energy level = 2n2
9. Angular momentum quantum number (l) Designates the shape of the orbital in which the electron is found Indicates the sublevel of the electron Values of l = successive integers from zero to n-1 (l = 0, 1, 2, …., n-1) Each energy level has a number of sublevels equal to the value of n. Energy level n=1 has 1 sublevel (l=0) Energy level n=2 has 2 sublevels (l=0 and l=1) Energy level n=3 has 3 sublevels (l=0, l=1, and l=2) Energy level n=4 has 4 sublevels (l=0, l=1, l=2, l=3) Commonly used labels of the sublevels l=0 is the s-sublevel l=1 is the p-sublevel l=2 is the d-sublevel l=3 is the f-sublevel
10.
11. Magnetic quantum number (ml) Determines the orientation of the orbital within the sublevel Each energy level has an s-sublevel that contains 1 s-orbital Beginning with the 2nd energy level, each energy level has a p-sublevel containing 3 p-orbitals. Beginning with the 3rd energy level, each energy level has a d-sublevel containing 5 d-orbitals. Beginning with the 4th energy level, each energy level has an f-sublevel, containing 7 f-orbitals Values of ml are integers from –l to +l Orbital – a region in the space surrounding the nucleus where the probability of finding an electron is above 90%
12. Spin quantum number (ms) Each orbital can hold a maximum of 2 electrons. Spin makes the electron act like a tiny magnet Values of ms are +1/2 or -1/2
