Link to Ionic Bonds Link to NaCl

Link to MgCl2

Link to Li2O

Link to AlBr3

Looking for Patterns in Covalent Lewis Dot Structures

Covalent Lewis Dot Structure Notation = nonbonding e- ; represents 1 e-; belong to only one atom Use to represent bonding pair of e- = e- e- = single bond (1 shared e- pair). Each dash represents 1 pair or 2 electrons. = e- e- = double bond (2 shared e-pairs) or 4 e- e- e- = e – e- e- = triple bond (3 shared e- pairs) or 6 e- e- e- e- Link to Notes

Why do atoms form chemical bonds? Lowest Energy Arrangement = Completely Filled Valence Electron Level Atoms gain, lose or SHARE valence electrons in order to obtain a completely filled valence electron level. First energy level: Filled = 1s2 All other energy levels = ns2np6 ↑↓ DUET RULE OCTET RULE ↑↓ ↑↓ ↑↓ ↑↓

For each group of elements: How many valence electrons do atoms in this group have? (Recall group # = # of valence e-) How many bonds ( ) is each atom making? How many nonbonding electrons (dots) does each atom have around it? How many total valence electrons does the atom have in the final bonded structure?

H H H F H Cl H Br H H C H H N H H O H H H H2 HF HCl HBr H2O NH3 CH4 What patterns do you notice about #’s of bonds ( ) and nonbonding electrons (dots) and total valence e- on H? H2 HF HCl HBr H2O NH3 CH4 H H H F H Cl H Br H H C H H N H H O H H H

Duet Rule Hydrogen always makes 1 covalent bond with no nonbonding electrons (dots) in order to fill the first energy level. H H H H H H H F H F

Group 7, Family 17 Halogen ns2np5 F Cl Br I

O O O F2 Cl2 Br2 I2 HF HCl HBr HI H H H H OF2 OCl2 OBr2 What patterns do you notice about the # of bonds ( - ) and number of dots ( ∙ ) for F, Cl, Br and I? F2 Cl2 Br2 I2 HF HCl HBr HI H H H H OF2 OCl2 OBr2 O O O

Octet Rule Each F, Cl, Br or I atom starts with 7 valence electron and forms 1 bond (2e-) with 3 nonbonding pairs (6e-) to end up with 8 valence electrons: F F F F x

Group 6 or Family 16 Elements

Group 6 Elements: O, S, Se H O H H S H H Se H H C O H H H O H C H S Se

Octet Rule Each O, S, or Se atom starts with 6 valence electron and forms typically forms 2 bonds and 2 nonbonding pairs to end up with 8 valence electrons: O O O O

Group 5, Family 15: N, P, As,

Group 5: N, P, As H N H H H As P H H H H H N N H N N H

Octet Rule Each N, P, or Sb atom starts with 5 valence electrons and typically forms 3 bonds with 1 nonbonding pair to end up with 8 valence electrons: N N N N

Group 4, Family 14: C, Si,

Group 4, Family 14: C, Si

Octet Rule Each C, or Si atom starts with 4 valence electrons and typically forms 4 bonds with 0 nonbonding pairs to end up with 8 valence electrons: O O C O C O

For each pattern, identify the element that could represent X Choices: A) H B) F C) C D) N E) O E) O 1) X A) H 2) X D) N 3) X 4) X C) C B) F 5) X

In hydroxide -1 ion, why does O make 1 bond instead of the usual 2? Ans: -1 charge means O has gained 1 valence e- and acts like an atom with 7 valence e- instead of an atom with 6 valence e-.

In ammonium + ion, why does N make 4 bonds here instead of the usual 3? Ans: + charge means N has lost 1 valence e- and acts like an atom with 4 valence e- instead of an atom with 5 valence e-.

Link to Notes

Draw the Lewis Dot Structure for CH2Cl2 Step #1: Determine Central Atom Formula Method: Single atom in formula = # of Bonds Method: Step #2: Connect all atoms with single bonds coming off central atom: C C =4 bonds, H =1, Cl =1 H Cl C Cl H

Draw the Lewis Dot Structure for CH2Cl2 3) Arrange dots so that each atom has filled outer energy level (Duet Rule for H, Octet Rule for Cl) H Cl C Cl H