«F_Name» «L_Name» Period «Per» Chapter 4 Section 3 «Num»
Chapter 4 Sec 3: Rules Governing Electron Configurations
No 2 electrons can be in the same Pauli Exclusion Principle states that no two electrons in the same atom space can have the same four quantum numbers. Every electron is different than all the other electrons in an atom.
Electron Configurations: the arrangement of electrons in an atom. An arrangement – the “certain way” the electrons are together
Configuration Notations: The model used to exhibit electron Electron arrangement written down configurations.
Aufbau Filling Principle An electron occupies the lowest orbital Energies are filled from the bottom up (energy) that can receive it. all orbitals in a group get one electron Hund’s Rule states that orbitals of equal energy are each occupied by one before any get 2; all first electrons electron before any are occupied by a second electron and all electrons in have the same spin direction singly occupied orbitals must have the same spin.
Examples of the p-orbital filling
sublevel = orbital This figure shows how two (a), three (b), and four (c) electrons fill the p sublevel of any given main energy level according to Hund’s rule. Since up and down are arbitrarily assigned, convention has given that we start orbital notation examples: with up and then down after the “up spin” has filled a sublevel.
«F_Name» «L_Name» Period «Per» «Num»
«F_Name» «L_Name» Period «Per» «Num» Orbital Notation In Orbital Notation, an unoccupied orbital is represented by a line, with the orbital’s name written underneath the line – the next step after the Bohr model
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1s An orbital containing one electron is represented as . An orbital containing two electrons is represented as , showing the electrons paired and with opposite spins.
Putting it all together: The lines are labeled with the principal quantum number and sublevel letter beneath the line.
For example, the orbital notations for Hydrogen, Helium, and Boron are written as follows.
Hund’s rule is followed when using this notation. For Example Oxygen’s notation is:
Electron-configuration notation eliminates the lines and arrows of orbital notation. Instead, the number of electrons in a sublevel is shown by adding a superscript to the sublevel designation.
Hydrogen’s Electron-configuration notation is 1s1. The superscript indicates that one electron is present in hydrogen’s 1s orbital.
Helium’s configuration is 1s2. The superscript indicates that there are two electrons in Helium’s 1s orbital. «F_Name» «L_Name» Period «Per» «Num»
2 2 1 Coefficient is the The electron configuration for Boron is 1s 2s 2p . principle quantum #; the The superscript indicates the number of electrons letter is the angular momentum quantum #; in each orbital. the superscript is the number of electrons, this indicates both the The electron configuration for Oxygen is magnetic quantum # and 1s22s22p4. The superscript indicates the number spin of electrons in each orbital.
Electron-configuration notation general Rule First write the Principle Quantum number (the energy level: same as the period on our periodic table). Then write the angular momentum quantum number (the orbital shape: s, p, d, or f) Finally, superscript the number of electrons in the orbital. (maxes: s 2, p6, d10, and f14) n l # of electrons in the orbital Principle Quantum Number: n (1 – 7) Angular Momentum Quantum Number: l (s, p, d, or f) # of electrons in the orbital (just the e –’s in the “l” orbital «F_Name» «L_Name» Period «Per» «Num»
Nobel Gas Configuration Neon’s electron configuration is 1s22s22p6
Phosphorus’s electron configuration is 1s22s22p63s23p3 Notice how Neon’s configuration is the first part of Phosphorus’s configuration.
Neon 1s22s22p6 Phosphorus 1s22s22p63s23p3
Just like you can substitute in a math equation, chemist substitute Neon’s configuration with Neon’s symbol Square bracketed to distinguish that it is Neon’s configuration and not Neon.
Similarly, all the noble gas configurations can be used to substitute into configurations as shorthand.
P’s Nobel - Gas Notation: [Ne] 3s23p3
This shorthand configuration is called Nobel - Gas Notation. See page 111, 112, and 114 for more examples.
«F_Name» «L_Name» Period «Per» «Num» Inner-Shell Electrons: electrons that are not in the highest occupied energy level. Highest Occupied Level: the electron-containing (has electrons in it) main energy level with the highest principal quantum number.
Draw Orbital Notation, Electron Configuration Notation, and Nobel - Gas Notation for fluorine, chlorine, bromine and iodine. (The halogens) F: 1s2 2s2 2p5 F: [He] 2s2 2p5
Cl: 1s2 2s22p6 3s23p5 Cl: [Ne] 3s23p5
Br: 1s2 2s22p6 3s23p63d10 4s24p5 Br: [Ar] 3d10 4s2 4p5
2 2 6 2 6 10 2 6 10 2 5 10 2 5 I: 1s 2s 2p 3s 3p 3d 4s 4p 4d 5s 5p I: [Kr]4d 5s 5p
Also a note about the Halogens and a few other elements of the Periodic Table: There are some elements that do not exist as single atoms in their elemental form. They exist as “pairs” and are called Diatomic elements The diatomic elements are hydrogen, nitrogen, oxygen, and the halogens: fluorine, chlorine, bromine, iodine, and astatine. Astatine is so rare in nature (its most stable isotope has a half-life of only 8.1 hours) that it is usually not considered. Many metals are also diatomic when in their gaseous states.
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