Molecular Shapes Created by: Ray Tedder Corresponds to Chemistry: Matter and Change, Ch 9.4.

 All your life you’ve been taught in things in 2 dimensions: Understanding and Drawing Electron Pair Shapes and Molecular Shapes: books Molecular Shapes TV movies classroom blackboards and whiteboards

 The real world is 3 dimensional... Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes but effective communication requires that 3 dimensional concepts be communicated in 2 dimensional represenations.

 Given the current state of communications technology, it is important to be able to represent things in 2 dimensions... Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes even 3 dimensional things.

 The shape of atoms, their orbitals, and of molecules is in 3 dimensions, Understanding and Drawing Electron Pair Shapes and Molecular Shapes: but on paper we must find a way to represent that 3 dimensional structure in 2 dimensions. Molecular Shapes

 This requires some mental gymnastics training, and few can do it without practice. Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes

 First, let’s review some things about Lewis dot diagrams. Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes  The dots represent electrons around an atom.  We put one on each side, and then start pairing them up.

 Nitrogen has 5 electrons in it’s valence energy level... Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes but--like all atoms--it wants 8 electrons in it’s valence level.  So it looks to share or exchange electrons to get there.

 Hydrogen has one electron to share. Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes  Since nitrogen has 3 lone electrons to share, we can put a hydrogen at each of those locations.  Nitrogen has the 8 electrons it wants.  The result is ammonia.

 This is a flattened out drawing. Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes  It does not show the actual 3 dimensional shape.  We need modifications.  We need electron pair and molecular geometry.

 We will be using a general form to explain electron pair and molecular geometry. Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes  For our electron pair geometry, “A” is the central atom in a molecule.

 We will arrange both the bonding pairs (shared) of electrons and the non- bonding pairs (lone pair) electrons so that they are as far apart as possible. Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes

 This drawing shows 8 electrons around a central atom... Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes the same as the 8 electrons around the nitrogen in ammonia.

Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes  Here’s the flattened out version... with the 8 electrons around the central atom.

 This drawing shows 8 electrons around a central atom... Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes the same as the 8 electrons around the nitrogen in ammonia.  Only this drawing shows the arrangement of electron pairs in space.

 The dotted line shows an electron pair out behind the central atom. Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes  The triangle shape shows an electron pair out in front of the central atom.  This is the “electron pair geometry.”

 Now we add atoms where 3 of those electron pairs are located. Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes  For ammonia, the “B” atoms are hydrogens.  This is the “modified electron pair geometry.”

 Now we remove the “lone pair.” Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes  This is the “molecular geometry.”

 This electron pair shape has a name: Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes If it has 4 corners, spaced around the central atom like this, then it’s a tetrahedral.

 This modified electron shape is also a tetrahedral because it also has 4 corners spaced in the same configuration. Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes

 This molecular shape has a name: Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes If it has 3 corners spaced around the central atom in this way, it’s a trigonal pyramidal shape.

 This electron pair shape is linear. Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes

 This molecular shape is also linear. Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes

 This electron pair shape is Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes trigonal planar.

 If we put atoms on every electron pair… Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes trigonal planar. B B B we get a molecular shape that is also called..

 This modified electron pair shape is trigonal planar. Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes

 When the lone pair is removed from the trigonal planar modified electron pair shape, the result is a bent molecular shape. Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes

 This electron pair shape is a tetrahedral. Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes

òIf atoms are to be placed where all 4 electron pairs are located, then the molecular shape is also tetrahedral. Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes B B B B

Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes B B B  If atoms are to be placed where 3 electron pairs are located, then the modified electron shape is also tetrahedral.

Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes B B B  But the molecular shape will be trigonal pyramidal.

 If atoms are to be placed where 2 electron pairs are located, then the modified electron shape is—again— tetrahedral. Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes B B

 But the molecular shape is called “bent.” Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes B B

 We can put the atoms on any of the 2 corners that we want to. Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes B B

 But the molecular shape is still called “bent.” Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes B B

Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes  This electron pair shape is trigonal bipyramidal. Notice that there are 2 different sized angles here. 120  90 

Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes  This electron pair shape is trigonal bipyramidal. Notice that there are 2 different sized angles here. 120  90 

Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes then the molecular shape is also B trigonal bipyramidal. are located, B B B B  If atoms are to be placed where all 5 electron pairs

Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes are located, then the modified electron pair shape is also trigonal bipyramidal. B B B B  If atoms are to be placed where 4 electron pairs

Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes B B B B  Notice that the unshared pair of electrons is in one of the equatorial positions. That’s because unshared pairs take up more space… and there’s more space on the equator.

Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes B B B  Notice that the unshared pair of electrons is in one of the equatorial positions. Around the equator there’s 120  to some of the shared pairs… but at the poles it’s 90  to everything. B

Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes B B B  Notice that the unshared pair of electrons is in one of the equatorial positions. Around the equator there’s 120  to some of the shared pairs… but at the poles it’s 90  to everything. B

B Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes  The molecular shape that results from this modified electron pair shape is... an irregular tetrahedron. B B B

Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes  If atoms are to be placed where 3 electron pairs are located, then the modified electron pair shape is also trigonal bipyramidal. B B B

electron pair shape is... Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes T-shaped planar. B B B  The molecular shape that results from this modified

Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes  If atoms are to be placed where only 2 electron pairs are located, then the modified electron pair shape is still called trigonal bipyramidal. B B

Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes linear. B B  The molecular shape that results from this modified electron pair shape is...

Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes  This electron pair shape is octahedral. Notice that there is only 1 size angle here. It’s 90  to everything.

Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes  This electron pair shape is octahedral.

Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes  If atoms are to be placed where all 6 electron pairs are located, then the molecular shape is also octahedral. BB B B BB

Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes are located, then the modified electron pair shape is also octahedral. B B B B B  If atoms are to be placed where 5 electron pairs

Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes  The molecular shape that results from this modified electron pair shape is... pyramidal. BB BB B

Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes  If atoms are to be placed where 4 electron pairs are located, then the modified electron pair shape is also octahedral. B B B B

electron pair shape is... Understanding and Drawing Electron Pair Shapes and Molecular Shapes: Molecular Shapes square planar.  The molecular shape that results from this modified BB BB

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