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Electron Configurations and the Periodic Table

Electron Configurations and the Periodic Table. Chapter 3 Section 2. Electron Configurations. Electron configuration – the arrangement of electrons in an atom The most important of these electrons are the valence electrons or outermost electrons. Valence Electrons.

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Electron Configurations and the Periodic Table

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  1. Electron Configurations and the Periodic Table Chapter 3 Section 2

  2. Electron Configurations • Electron configuration – the arrangement of electrons in an atom • The most important of these electrons are the valence electrons or outermost electrons.

  3. Valence Electrons • The number of valence electrons for all representative elements is determined by the number of the group in which the atom is found. • Examples • Hydrogen - Group IA or 1 • 1 valence electron. • Fluorine – Group VIIA or 17 • 7 valence electrons

  4. NOW YOU TRY! How many valence electrons do the following elements contain? A. Lithium B. Carbon C. Aluminum D. Sulfur E. Krypton 1 4 3 6 8

  5. So, who cares? Valence electrons are important because they determine how atoms interact with each other to form compounds!

  6. Arrangement of Electrons in Atoms according to the Quantum Mechanical Model Electrons in atoms are arranged as ENERGY LEVELS SUBLEVELS ORBITALS

  7. Energy Levels • Think of the energy level as the relative distance from the nucleus. Currently, all electrons for known elements will occupy the first seven levels, but there is a possibility of infinite levels. 2 1 3

  8. Sublevels AKA Subshells • The sublevels are named s, p, d, and f and are listed in increasing energy. • We specify both the energy level and sublevel when describing an electron, i.e. 1s, 2s, 2p.

  9. Determining the number of sublevels • The first energy level has 1 sublevel “1s”. • The second energy level has 2 sublevels “2s and 2p”. • How many sublevels exist on the 3rd energy level? • What would they be called? 3 3s, 3p, & 3d

  10. The p sublevel has 3 orbitals. They are called px, py, and pz. Orbitals Orbital – a specific region of a sublevel containing a maximum of 2 electrons. The s sublevel has 1 orbital. The d sublevel has 5 orbitals. The f sublevel has 7 orbitals.

  11. Shapes of Orbitals Typical s orbital (sphere) (peanut) (double peanut) Typical f orbital (flower)

  12. How many electrons can be in a sublevel? Remember: A maximum of two electrons can be placed in an orbital. s sublevel p sublevel d sublevel f sublevel Number of orbitals 1 3 5 7 Number of electrons 6 10 14 2

  13. Aufbau Principle • An electron occupies the lowest-energy orbital that can receive it. • This guides how electron configurations are written.

  14. Rules to Remember when Writing Electron Configurations • Obtain the number of total electrons from the periodic table. • Electrons occupy the lowest energy orbitals first. • Each energy level (n) only contains n sublevels. • The s sublevel holds 2 e-, the p 6 e-, the d 10 e-, and the f 14 e-. • Follow the filling pattern only moving once each sublevel is full.

  15. Filling Pattern

  16. Periodic Table Method Steps: • Find the element for which you are writing the configuration. • Starting with Hydrogen, write down the energy level and sublevel. • Count the boxes in the sublevel and add it as a superscript. • Continue moving through the sublevels until you reach your destination.

  17. Electron Configurations 3d7 Number of electrons in the sublevel Energy Level Sublevel 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14…etc.

  18. Let’s Try It! • Write the electron configuration for the following elements: H C N Br S

  19. Let’s Try It! • Write the electron configuration for the following elements: H 1s1 C 1s2 2s22p2 N 1s2 2s22p3 Br 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5 S 1s2 2s2 2p6 3s2 3p4

  20. Noble Gas Notation • A way of abbreviating long electron configurations • Since we are only concerned about the outermost electrons, we can skip to places we know are completely full (noble gases), and then finish the configuration

  21. Noble Gas Notation • Step 1: Find the closest noble gas to the atom, WITHOUT GOING OVER the number of electrons in the atom. Write the noble gas in brackets [ ]. • Step 2: Find where to resume by finding the next energy level (row in periodic table). • Step 3: Resume the configuration starting with ns2where n is the next level

  22. Noble Gas Notation • Chlorine • Longhand is 1s2 2s2 2p6 3s2 3p5 You can abbreviate the first 10 electrons with a noble gas, Neon. [Ne] replaces 1s2 2s2 2p6 The next energy level after Neon is 3 So you start at level 3 on the diagonal rule (all levels start with s) and finish the configuration by adding 7 more electrons to bring the total to 17 [Ne] 3s2 3p5

  23. Practice Noble Gas Notation • Write the noble gas notation for each of the following atoms: Cl P O I

  24. Practice Noble Gas Notation • Write the noble gas notation for each of the following atoms: Cl [Ne]3s2 3p5 P [Ne]3s2 3p3 O [He]2s22p4 I [Kr]5s2 4d10 5p5

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