1 Daily Science Name the following: HBr H 2 SO 3 P 3 O 5 Label the following as being an ionic bond or covalent bond: NaCl Iron (III) oxide Dinitrogen pentoxide Ca 3 (PO 3 ) 2 PCl 5

2 Pg. 55

3 Structural Formulas Used to show relative positions of atoms Use lines for bonds Structural formulas are made from Lewis structures

4 Symbols for Lewis structures = an electron = an electron pair (lone pair) = single bond (σ bond)- 2 electrons = double bond (σ and π)-4 electrons = triple bond (σ and 2 π)- 6 electrons

5 Steps for drawing Lewis Structures 1. Determine the number of valence electrons for each element 1. Sum the valence electrons for all the elements 2. Determine which atom will be the central atom and connect each element with a line. 1. H and halogens are always terminal 2. Least electronegative is the central atom 3. First atom listed is USUALLY the central atom 3. Each atom (except H and He) must have 8 electrons around it (octet). Complete each octet by adding lone pairs. 4. Count the number of electrons in your structure 1. Too many electrons, cross out a lone pair from the central atom and a terminal atom (except H and He) and create a multiple bond 2. Recount and repeat until the total number of electrons equals the number from number 1

6 Examples CCl 4 NF 3 CO

7 Expanded valence If your total number of electrons in the last step is less than the total in number 1, add a lone pair around the central atom. This can occur from the 3 rd period down Called an expanded valence Ex. SeCl 4 and PCl 5

8 Lewis structures of ions Do the same steps and add the extra electrons that are with the ion If the ion is positive, subtract electrons If the ion is negative, add electrons Ex. SO 4 2-

9 Practice Pg. 56 Create a chart like the following taking up the WHOLE page FormulaTotal Valence Lewis Structure # of σ bonds # of π bonds CO 3 2- NO 3 - H2SH2S H3O+H3O+ PO 3 -3 PF 5 ClCN CH 2 O OF 2 H2OH2O