Yr 10 Chemistry 3D Structures of Molecules

 Questions of Doom Starter

 TO KNOW how to work out the electronic structure from group and period number  TO BE ABLE to draw the 3D Shapes for molecules  TO UNDERSTAND the rules for drawing Lewis structures Objectives

 C  B  Na  Ne  Ca 2+  Cl 1- Draw the Lewis Structures for Single Atoms: Revision

1.Pick a central atom (usually the one with the least number of atoms) 1.Put other atoms around (usually equally spaced) 2.Put pairs of electrons around each atom (as if it has a full valence shell. SO 4 2-

3.Add up the total number of valence electrons 4.Adjust for charge if it is a poly atomic ion  Add electrons for negative charges  Reduce electrons for positive charges Example SO 3 2-  1 S = 6 e  3 0 = 6x3 = 18 e  (2-) charge = 2 e Total = 26 e 6

Electron Dot Structures 5.Use double or triple pairs if have too many electrons on your diagram 6.If you have extra electrons put them on the central atom 7

 Don’t forget to Follow the rules.  Don’t forget to draw in ELECTRON LONE PAIRS Draw the Lewis structures for Molecules SiCl 4 CH 4 NH 4 +

 SF2  CO2  CO  SHF  CH2ClF Try these…………

Advanced structural drawings (3D)  The dashed wedge = bond going back  Solid wedge = bond going forward  Unbroken line = plane of the paper

Basic Molecular shapes The most common shapes of molecules are shown at the right 13

Linear Molecules Linear molecules have only two regions of electron density. 14

Angular or Bent Angular or bent molecules have at least 3 regions of electron density, but only two are occupied 15

Triangular Plane Triangular planar molecules have three regions of electron density. All are occupied by other atoms 16

Tetrahedron Tetrahedral molecules have four regions of electron density. All are occupied by other atoms 17

Trigonal Bipyramid A few molecules have expanded valence shells around the central atom. Hence there are five pairs of valence electrons. The structure of such molecules with five pairs around one is called trigonal bipyramid. 18

Octahedron A few molecules have valence shells around the central atom that are expanded to as many as six pairs or twelve electrons. These shapes are known as octahedrons 19

Chemistry Shapes Sets ( group of bonding pairs) Lone Pairs Shape 20Linear 22Bent 30Triagonal Planar 31Pyramidal 40Tetrahedral