1. Yr 10 Chemistry Lewis Structures

2.  Questions of Doom Starter

3.  TO KNOW how to work out the electronic structure from group and period number  TO BE ABLE to draw the atomic structures to show covalent bonding  TO UNDERSTAND the rules for drawing Lewis structures Objectives

4.  Ionic Bonding is between a METAL and NON-METAL  Covalent bonding is between TWO NON METALS Remember…….

5. Covalent bonding in hydrogen chloride Both hydrogen (1) and chlorine (2.8.7) needs 1 more electron to attain a full outer shell. H (2) Cl (2,8,8) H-Cl Cl (2,8,7) H (1)

6. Covalent bonding in water Hydrogen (1) needs 1 more electron but oxygen (2.6) needs 2 more. Therefore, we need 2 hydrogens. O H H O H H O H H

7.  Hydrogen (1) needs 1 more electron. How many does nitrogen (2.5) need? How many hydrogens per 1 nitrogen? Draw bonding diagrams for ammonia. N H H H N H H H 3 3

8.  Hydrogen (1) needs 1 more electron. How many does carbon (2.4) need? How many hydrogens per 1 carbon? Draw bonding diagrams for methane. 4 4 C H H H H C H H H H

9. H H O O H H O O  Copy the atoms below.  Complete the diagram showing how each atom can achieve full shells.

10. Covalent bonding - multiple bonds  Mostly electrons are shared as pairs.  There are some compounds where they are shared in fours or even sixes.  This gives rise to single, double and triple covalent bonds.  Again, each pair of electrons is often represented by a single line when doing simple diagrams of molecules. Cl-Cl Single bond O=O Double bond N=N Triple bond

11. Chemical structures  Need to show the structure of a molecule.  Will use Lewis structures (electron dot diagrams) to show where there are lone pairs (filled orbitals) and bonding pairs (places where bonds most likely occur)

12. Drawing Lewis StructuresLewis Structures 1.Look at valence electrons of all atoms 2.Pick a central atom (least electronegative usually, has most bonding sites) 3.Align all atoms so that each have their ideal amount of valence electrons achieved through sharing.

13. Writing Dot Structures Writing Dot structures is a process: 1.Determine the number of valence electrons each atom contributes to the structure 2.The number of valence electrons can usually be determined by the column in which the atom resides in the periodic table 13

14. Writing Dot Structures 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 14

15. Electron Dot Structures 5.Make the atom that is fewest in number the central atom. 6.Distribute the electrons so that all atoms have 8 electrons. 7.Use double or triple pairs if you are short of electrons 8.If you have extra electrons put them on the central atom 15

16. Electron Dot Structures Example 2: SO 3  1 S = 6 e  3 O = 6x3 = 18 e  no charge = 0 e --------- Total = 24 e Note: a double bond is necessary to give all atoms 8 electrons 16

17. Electron Dot Structures Example 3: NH 4 +  1 N = 5 e-  4 H = 4x1 = 4 e-  (+) charge = -1 e- --------- Total = 8 e- Note: Hydrogen atoms only need 2 e- rather than 8 e- 17

18. Example -- Carbon Dioxide CO 2 1. Central atom = 2. Valence electrons = 3. Form bonds. 4. Place lone pairs on outer atoms. This leaves 12 electrons (6 pair). 5.Check to see that all atoms have 8 electrons around it except for H, which can have 2. C 4 e - O 6 e - x 2 O’s = 12 e - Total: 16 valence electrons

19. Carbon Dioxide, CO 2 There are too many electrons in our drawing. We must form DOUBLE BONDS between C and O. Instead of sharing only 1 pair, a double bond shares 2 pairs. So one pair is taken away from each oxygen atom and replaced with another bond. C 4 e- O 6 e- X 2 O’s = 12 e- Total: 16 valence electrons How many are in the drawing?

20. Practice Lewis structure and state the shape  SO 2  SO 3  [SO 4 ] - 2  AsCl 3  SI 2  CH 3 F  CH 2 F 2  NH 4 +  NO 2 -  NO 2 +  H 3 O +