1 / 23

Electron Configurations II

F. Schifano , Department of Science Bayonne High School, Bayonne NJ. Electron Configurations II. Key Skills:. What are Valence Electrons?. The valence electrons of an element are the outermost electrons.

phillip-tassos
Télécharger la présentation

Electron Configurations II

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. F. Schifano, Department of Science Bayonne High School, Bayonne NJ Electron Configurations II

  2. Key Skills:

  3. What are Valence Electrons? • The valence electrons of an element are the outermost electrons. • Only s and pelectrons in an atom’s highest energy level count as valence electrons.

  4. Determining the # of Valence e-

  5. Electron-Dot (Lewis) Diagrams Represent Valence Graphically • Each side represents a sub-orbital. • s-orbitals get both electrons first. • Each p sub-orbital gets one e- before any p-sub-orbital gets two. • This is called Hund’s Rule.

  6. Writing Electron-Dot Diagrams

  7. Practice • Determine the number of valence electrons in each of the following elements. Then draw their dot diagrams: • Ca • F • Br • Sr • N • O

  8. Why are Valence Electrons Special? • Formation of Covalent Bonds • When molecules get close to each other, the valence electrons are attracted to the nucleus of the other atom.

  9. Valence Electrons Form Bonds • If trading or sharing electrons would make both atoms more stable, this temporary attraction becomes a full-fledged chemical bond.

  10. Valence Electrons Predict Chemical Behavior • If two elements have the same number of valence electrons, they will react in a very similar way. • They need similar changes in their electron configuration to become stable.

  11. Practice • Which ones should have similar properties and react in similar ways? • Ca • F • Br • Sr • N • O

  12. The Holy Grail: Valence = 8 • The most stable configuration of electrons most atoms can have is valence = 8, also known as the octet configuration. • In chemical reactions, most atoms just take the simplest path to valence = 8.

  13. Noble Gases Are Already Stable • Neon, argon, krypton, radon, and xenon are all called noble gases. • They already have valence=8 . They don’t benefit from reacting, so they don’t react!

  14. Same Column = Same Valence • The periodic table is designed in just such a way that elements with the same valence fall into the same vertical column.

  15. Four Families

  16. Special Cases • Hydrogen becomes stable at valence = 0 or at valence = 2. • It can give away an electron, becoming valence =0 (H+) or it can gain an electron, becoming valence =2 (H-). • Helium is already stable at valence =2. • Like the other noble gases, helium is already stable and doesn’t react. • Boron is stable at valence =6.

  17. Writing Configurations Using the Periodic Table • An element’s position on the periodic table tells you the last electron that filled its orbitals: • Period (horizontal) = energy level • Block = orbital shape • Box number = #e- in the orbital. • Aufbau principle tells you all the rest!

  18. Writing Configurations Using the Periodic Table • Sulfur is in the fourth box of the third row, in the p-block. • Its last electron is 3p4. • Aufbau principle says everything under 3p4 must be filled, so: • 1s2 2s2 2p6 3s2 3p4.

  19. D-Block and F-Block Exceptions • If an element is in the d-block its last orbital will really be one energy level down from the row it’s in. • Last electron in chromium (Cr) = 3d4, NOT 4d4 • If an element is in the f-block its last orbital will really be two energy levels down from the row it’s in. • Last electron in plutonium (Pu) = 5f5, NOT 6f5

  20. Noble Gas Notation • Longer configurations are a chore. • Noble gases can be used as starting points for longer configurations.

  21. Using Noble Gas Notation

  22. Noble Gas Notation Cr =1s2 2s2 2p6 3s2 3p6 4s2 3d4 Ar = 1s2 2s2 2p6 3s2 3p6 ____________________________ So we can write the configuration of Cr as [Ar] plus the difference: [Ar] 4s2 3d4

  23. Questions • What are valence electrons?

More Related