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Chemistry- Unit 3 Section II - Chapter 7 (7.6-7.8, 7.11) Quantum Mechanics Atomic Review What subatomic particles do you get to “play” with? Protons → NO! It would change the element Neutrons → Don’t Care - isotopes: only mass is different Electrons → What we “play with” in chemistry Bohr Model of the Atom • electrons must circle the nucleus of an atom in certain paths • Developed the concept of Energy Levels Bohr Model of the Atom • The model correctly fits the quantized energy levels of the hydrogen atom and postulates only certain allowed circular orbits for the electron • Bohr’s model is incorrect. This model only works for hydrogen • Electrons do not move around the nucleus in circular orbits Quantum Mechanics • Quantum (definition from Webster’s) 1) quantity, amount 2) any of the very small increments or parcels into which many forms of energy are subdivided • Quantum Theory -describes mathematically the wave properties of electrons and other very small particles *electrons were determined to have a dual waveparticle nature *uses two principles Quantum Mechanics • Heisenberg uncertainty principle it is impossible to determine simultaneously both the position and velocity of an electron or any other particle • Schrodinger Wave Equation treats electrons as waves around the nucleus Together these two principles determine the probability of finding electrons We do not know the detailed pathway of an electron Quantum Mechanics Orbital three-dimensional region around the nucleus that indicates the probable location of an electron To describe orbitals, we use….. Quantum Numbers specify the properties of atomic orbitals and the properties of electrons in orbitals there are 4 quantum numbers Quantum Numbers • Principal quantum number (n) – size and energy of the orbital – the main energy level occupied by the electron • positive integers • ranges from 1 to 7 • equal to the period Quantum Numbers • Angular momentum quantum number (l or l) – shape of atomic orbitals – sometimes called a subshell • Orbitals possible is equal to n • Values of l are all integers less than l = n-1 Quantum Numbers • Angular momentum quantum number (l or l) l 0 1 2 3 subshell s p d f Quantum Numbers • Angular momentum quantum number (l or l) Concept Check For principal quantum level n = 3, determine the number of allowed subshells (different values of l), and give the designation of each. # of allowed subshells = 3 l=0 3s l=1 3p l=2 3d Quantum Numbers • Magnetic quantum number (ml) – orientation of the orbital in space relative to the other orbitals around the nucleus – ml = ±l • each subshell has a specific shape – s subshell has 1 orbital one shape – p subshell has 3 orbitals three shapes – d subshell has 5 orbitals five shapes – f subshell has 7 orbitals seven shapes • Assign each family magnetic quantum number then repeat if needed You do NOT need to know the shapes Quantum Mechanics • Electron spin quantum number (ms) – an orbital can hold only two electrons, and they must have opposite spins – can be -½ or +½ • Each electron must be distinguishable (different) from all others • Start with the negative spin first Quantum Mechanics Quantum Numbers for the First Four Levels of Orbitals in the Hydrogen Atom Quantum Mechanics 1s Orbital Quantum Mechanics Two Representations of the Hydrogen 1s, 2s, and 3s Orbitals Quantum Mechanics 2px Orbital Quantum Mechanics 2py Orbital Quantum Mechanics 2pz Orbital Quantum Mechanics The Boundary Surface Representations of All Three 2p Orbitals Quantum Mechanics 3dx -y Orbital 2 2 Quantum Mechanics 3dxy Orbital Quantum Mechanics 3dxz Orbital Quantum Mechanics 3dyz Orbital Quantum Mechanics 3d z 2 Orbital Quantum Mechanics The Boundary Surfaces of All of the 3d Orbitals Quantum Mechanics Representation of the 4f Orbitals in Terms of Their Boundary Surfaces Concept Check For l = 2, determine the magnetic quantum numbers (ml) and the number of orbitals. magnetic quantum numbers = –2, – 1, 0, 1, 2 number of orbitals = 5 Quantum Mechanics Identify the four quantum number for the following elements: Element Lithium Bromine Silver Uranium n 2 4 5 7 l 0 1 2 3 ml 0 0 1 -1 ms -½ +½ +½ -½ Concept Check Identify the four quantum number for the following elements: Element Platinum Silicon Chlorine Radium n 6 3 3 7 l 2 1 1 0 ml 0 0 0 0 ms +½ -½ +½ +½ Concept Check Identify the four quantum number for the following elements: Element Potassium Iron Arsenic Tungsten n 4 4 4 6 l 0 2 1 2 ml 0 -2 1 1 ms -½ +½ -½ -½ Quantum Mechanics Electron Configurations • the arrangement of electrons in an atom based on 3 rules • Aufbau principle – electrons occupy the lowest energy level they can • Pauli exclusion principle – in a given atom, no two electrons can have the same set of four quantum numbers Quantum Mechanics Electron Configurations • Hund’s Rule – the lowest energy configuration for an atom is the one having the maximum number of unpaired electrons allowed by the Pauli principle in a particular set of degenerate (same energy) orbitals • orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron • all electrons in singularly occupied orbitals must have the same spin Quantum Mechanics Orbital Energies Quantum Mechanics Orbital Energies Quantum Mechanics The Orbitals Being Filled for Elements in Various Parts of the Periodic Table Quantum Mechanics Electron Configuration Notation • The order that electrons fill orbitals 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10 7p6 Quantum Mechanics Electron Configuration Notation What is the electron configuration for oxygen? 1s2 2s2 2p4 What is the electron configuration for bromine? 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5 Quantum Mechanics Electron Configuration Notation • Instead of using the Periodic Table, you can make this chart to write electron configurations. Quantum Mechanics Electron Configuration Notation What is the electron configuration for Strontium? 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 What is the electron configuration for Erbium (Er)? 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f12 Review page 315 and 316 in book Quantum Mechanics Noble Gas Configuration Notation • You can also use Noble Gases to show electron configurations since they have a fulfilled Octet Rule To do this, go backwards from your element to the closest Noble Gas and list it in brackets [ ] Starting from that point, list the electron configuration to your element • It is really the same thing; it just shortens the configuration up. • Don’t use a Noble Gas Configuration unless asked to do so. Quantum Mechanics Noble Gas Configuration Notation What is the Noble Gas configuration for Chlorine? [Ne] 3s2 3p5 What is the Noble Gas configuration for Einsteinium (Es)? [Rn] 7s2 5f11 Quantum Mechanics Orbital Diagram • A notation that shows how many electrons an atom has in each of its occupied electron orbitals. • Always draw up arrows (-½ spin) first Oxygen: 1s22s22p4 Oxygen: 1s 2s 2p Quantum Mechanics Orbital Diagram • Draw an orbital diagram for sulfur. Sulfur: 1s22s22p63s23p4 3s 2s 1s 2p 3p Concept Check Determine the expected electron configurations for each of the following. a) S 1s22s22p63s23p4 b) Ba 1s22s22p63s23p64s23d104p65s24d105p66s2 c) Eu 1s22s22p63s23p64s23d104p65s24d105p66s24f7 Concept Check Determine the expected Noble Gas configurations for each of the following. a) S [Ne]3s23p4 b) Sr [Kr]5s2 c) Au [Xe]6s24f145d9 Concept Check Draw an Orbital Diagram for Aluminum. 3s 2s 1s 2p 3p Quantum Mechanics Valence Electrons • The electrons in the outermost principal quantum level of an atom 1s2 2s22p6 (valence electrons = 8) • The elements in the same group on the periodic table have the same valence electron configuration • Only going to be responsible for Main Group elements • Range is from 1 to 8 Quantum Mechanics Valence Electrons • Chlorine – 1s22s22p6 3s23p5 [Ne] 3s23p5 7 valence electrons • The number of valence electrons is equal to the group number minus 10 (unless it is a single digit, then it is the number of valence electrons) Concept Check Determine the valence electrons for the following elements: a) S 6 b) Sr 2 c) B 3 Unit 3 Homework Set #2 pg 332: #67, 68, 70, 75, 76, 77, 79, 84, 89, 92, 132 (11)