What are molecular orbitals? QUANTUM MODEL notes 2 Mr.Yeung
Recall, the quantum model is about electrons behaving both a wave and a particle. Electrons are in areas of calculated probability, these are your orbitals.
ELECTRON S ADDRESS QUANTUM MODEL CONTINUED To locate the exact address of the electrons, there are 3 quantum numbers or clues to use: Principal quantum number: (n) Size n = 1, 2, 3, 4, 5 Angular quantum number: (l) Shape l = s, p, d, or f Magnetic quantum number (m): Orientation m = +1/2 or -1/2 These 3 quantum numbers give you the size, shape and orientation of the electrons
ELECTRON S ADDRESS QUANTUM MODEL CONTINUED To locate the exact address of the electrons, there are 3 quantum numbers or clues to use: Principal quantum number: (n) Size n = 1, 2, 3, 4, 5 Angular quantum number: (l) Shape l = s, p, d, or f Magnetic quantum number (m): Orientation m = +1/2 or -1/2
ELECTRON S ADDRESS QUANTUM MODEL CONTINUED To locate the exact address of the electrons, there are 3 quantum numbers or clues to use: 2 electrons max Principal quantum number: (n) Size n = 1, 2, 3, 4, 5 Angular quantum number: (l) Shape 6 electrons in total l = s, p, d, or f Magnetic quantum number (m): Orientation m = +1/2 or -1/2 Each orbital can occupy a maximum of 2 electrons in opposite spins 10 electrons in total
Principal Quantum Number The energy level of the element Identified by going down the rows of the periodic table Gives the size Angular Quantum Number Gives the shape: s has spherical shape p has dumbbell shape d has 5 orbitals f has 7 orbitals Magnetic quantum number Gives the spin of the electrons
S orbital d orbitals p orbitals Helium goes with S f orbitals
Since each orbital can have a maximum of 2 electrons, let s see how this relates to the Periodic table. 2 electrons 6 electrons 10 electrons 14 electrons
How many total orbitals are there in energy level 2? 2s 2 There is 1 s orbital 2p 6 There is 1px, 1py, 1pz orbital How many total electrons in energy level 2? Total of 4 orbitals Each orbital can hold a maximum of 2 electrons Therefore, 8 total electrons
How many total orbitals are there in energy level 3? 3s 2 3p 6 There is 1 s orbital There is 1px, 1py, 1pz orbital 3d 10 There are 5 orbitals How many total electrons in energy level 3? Total of 9 orbitals Each orbital can hold a maximum of 2 electrons Therefore, 18 total electrons
WHAT IS THE BIG PICTURE? The address of the energy level, the shape of orbital, the number of electrons of an element can be found. This is called the electron configuration
SOME EXAMPLES Energy level 1 s orbital 2 electrons Therefore, the location of electrons address is: 1s 2 This is called electron configuration
SOME EXAMPLES Chlorine has atomic number 17 The electrons have to build up to 17 1s 2 2s 2 2p 6 3s 2 3p 5 Therefore, the location of electrons address is: 1s 2 2s 2 2p 6 3s 2 3p 5
SOME EXAMPLES Potassium has atomic number 19 The electrons have to build up to 19 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 Therefore, the location of electrons address is: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2
Electron configurations follow 3 Principles: Aufbau Principle Pauli Exclusion Rule Hund s rule Electrons have to fill up all the free orbitals before filling German for To build up - start at lowest energy then build up to higher energy levels Only 2 electrons can occupy 1 orbital with opposite spins
For higher elements such as ones in the d sub-level and f sub-level, you must follow the correct energy sequence as the energy levels do not always go in order.
A useful tool to use to write the sequence of the electron configuration build up
SOME EXAMPLES Selenium has atomic number 34 The electrons have to build up to 34 1s 2 2s 2 2p 6 3s 2 3p 6 3d has lower energy than 4p 4s 2 3d 10 4p 4 Therefore, the location of electrons address is: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 4
Recap: Electrons function as waves and particles Electrons are found in regions of space calculated from Schrodinger s Wave equation 3 Principle Quantum numbers that determine where the electrons are located: n, l and m Quantum numbers provide different sizes, shapes and spins Electron configuration locates the electrons in terms of energy level and shape Electron configurations are based on 3 principles, Aufbau, Pauli s exclusion rule, and Hund s rule