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Understanding Matter Part II Beyond the Bohr model
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ELECTRON CONFIGUIRATION SHELL DIAGRAM
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Quantum Mechanical Model As we saw earlier, the Bohr Model had several short comings Krypton does not follow the 2, 8, 8 pattern. In order for Krypton to have enough electrons for 36 it needs an extra 18 electrons. The model currently used to describe the atom is the Quantum Mechanical Model of the atom This is the current theoretical framework that is used to describe all of the information we have about atoms and how they function
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Definitions Quantum (plural ‘quanta’) A finite amount of energy i.e. – an energy level in an atom The amount of energy required to move an electron from its present energy level to the next higher one Electrons can only have specific energy levels and nothing inbetween. Mechanical Movement of parts in relation to a whole i.e. – electrons in an atom Hence the Quantum Mechanical Model deals with the movement and location of electrons in an atom
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Uncertainty Principle We cannot know where an electron is and where it is going Because of this, we use probability to determine where an electron is most likely to be Using the electron probabilities, we find areas where electrons are most likely to be These areas are called electron clouds where the probabilities of finding electrons is very high The shapes and distance from the nucleus of these electron clouds depends on several factors
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Quantum Numbers To describe electron clouds and where electrons probably are, we use quantum numbers There are a total of four (4) quantum Principal Quantum Number Angular Quantum Number Magnetic Quantum Number Spin Quantum Number We will be concerned with theses 2
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Principal Quantum Number Energy level Distance away from the nucleus As # increases, distance from the nucleus also increases As the number increases, so does the energy of the electrons in those orbitals Represented by integers 1,2,3,4,5,6,7 that correspond to the seven horizontal rows on the periodic table Determined by counting as you move down (top to bottom) the periodic table
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Angular Quantum Number Also known as “sub-shells” Refer to the shape of the orbital There are four (4) different shapes S, P, D, F These correspond to the s, p, d, f blocks on the periodic table
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Periodic table shows Quantum Structure Energy increases as you go down the periods Subshell s Subshell p Subshell d Subshell f
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Sub-Shells S” Sub-shell Spherical shape Only one (1) orbital per energy level The 1 sub shell can hold 2 electrons “P” Sub-shell Dumbbell shape Three (3) orbitals per energy level Each shell can hold 2 electrons 3 orbitals mean the p-shell can hold up to 6 electrons
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Sub-Shells Continued “D” Sub-shell Tend to have a clover-leaf shape Five (5) orbitals per energy level Each can hold a maximum of two (2) electrons Can hold a max of 10 electrons “F” Sub-shell Shape contains 6 lobes for the most part Seven (7) orbitals per energy level Each can hold a maximum of two (2) electrons Fourteen 14 electrons total at each energy level
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To Summarize
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Modeling the Quantum Atom Krypton
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Potassium
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Manganese
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Three principles for electrons filling Shells Aufbau Principle: Electrons enter sub-shells of lowest energy first 1 st energy level fills up before the next Pauli Exclusion Principle: All atomic sub-shells contain a maximum of two (2) electrons. Each MUST have a different spin Hund’s Rule: when electrons occupy sub-shells of equal energy, ONE electron enters EACH sub-shell until all the sub-shells contain one electron with identical directions Electrons are added to sub-shells so that a maximum number of unpaired electrons result
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ELECTRON CONFIGUIRATION ORDER OF FILLING ORBITALS Orbitals are filled in increasing order of energy Different blocks on the periodic table (shaded in different colors in this chart) correspond to different types of orbitals. The periodic table, from left to right, shows the ‘basic’ pattern of sub- shell filling.
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Cheat Note
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Orbital Notation and Electron Configuration ORDER OF FILLING ORBITALS - HUND’S RULE The lowest energy stability of atom is attained when the number of electrons with the same spin is maximized
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Lets Try Oxygen
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Oxygen
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Lets Try Aluminum
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Aluminum
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Lets Try Chlorine
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Chlorine
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Nobel Gas notation An even more simplified and shorthand method for representing electron configuration. Emphasizes the outermost energy level only Instead of listing every energy level and amount of electrons individually, it utilizes the nearest noble gas element of the energy level below as a representation of the inner energy levels
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Nobel Gas Notation Example For Example: Sulfur Electron configuration would be: 1s 2 2s 2 2p 6 3s 2 3p 4 Its Noble Gas Notation would be: [Ne] 3s 2 3p 4 …this is because we know that the electron configuration of Ne is: 1s 2 2s 2 2p 6, therefore there is no need to write it all out.
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Nobel Gas Examples
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Examples Continued
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Nobel Gas Notation Noble Gas Configurations are especially useful for elements with a large atomic number, as their complete electron configurations become tiresome & redundant to write out each time.
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You Try Complete Orbital and noble gas practice sheet. For additional practice you could try: Write out the orbital diagram and electron configuration of all even number elements up to 18 Write out the Nobel gas notation for each of the following elements. Ca, Br, Nd, U, Co and Au
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