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The Shapes of Molecules

The Shapes of Molecules. Year 12 Chemistry. Learning Outcomes. How to answer this question. Write: “The molecule has” then one of : 4 non-central atoms so the shape is tetrahedral because the 4 “ espeao “. (“electron sets push each other away.”)

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The Shapes of Molecules

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  1. The Shapes of Molecules Year 12 Chemistry

  2. Learning Outcomes • How to answer this question. Write: “The molecule has” then one of: • 4 non-central atoms so the shape is tetrahedral because the 4 “espeao“. (“electron sets push each other away.”) • 3 non-central atoms and no non-bonding pairs so the shape is trigonal planar because the 3 “espeao”. • 3 non-central atoms and onenon-bonding pair so the shape will be trigonal pyramidal because the 4 “espeoa”. • 2 non-central atoms and no non-bonding pairs so shape is linear because the 2 “espeoa”. • 2 non-central atoms and one non-bonding pairs so shape is bent because the 3 “espeoa”. • 2 non-central atoms and two non-bonding pairs so shape is bent because the 4 “espeoa”.

  3. The shapes of molecules The 5 shapes are • Linear • Bent or “V-shaped” • Trigonal Planar • Trigonal Pyramidal • Tetrahedral

  4. The shape of a molecule • Depends on the number of outer (non- central) atoms and the number of non-bonding electron pairs on the central atom. • The non-bonding pairs push the bonds away.

  5. 1. Linear molecules • All molecules with only two atoms are linear • Example: oxygen, O2 • All molecules with 3 atoms and no non-bonding pairs on the central atom are linear • Example: carbon dioxide, CO2

  6. 2. Bent or “V” shaped • Where there are 3 atoms and 1 or more non-bonding pairs on the central atom. • Water is a bent shape because there are 2 non bonding pairs of electrons on the central oxygen atom.

  7. 3. Trigonal planar • Where there are 4 atoms, and no non-bonding pairs on the central atom. • Methanal H2CO is trigonal planar. • Bond angle is 120° (=360/3)

  8. 4. Trigonal pyramidal • Where there are 4 atoms, and 1 non-bonding pair on the central atom. • Ammonia, NH3 is trigonal pyramidal • Bond Angle is 109°

  9. 5. Tetrahedral • Where there are 5 atoms. • methane, CH4 is tetrahedral. • Bond angle is 109°

  10. Exam questions on shapes of molecules • Question 2. Name the shape of a molecule and explain why it has this shape • 2006 (a) SF2 (b) CO2 (c) PBr3 • 2007 (a) CH3Cl (b) CH2O (c) NCl3 • 2008 (a) CH4 (b) PCl3 • 2009 (a) H2O, (b) CO2, (c) CH2Br2 (d) NCl3 (e) SO3

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