Lets review Oxygen Symbol Atomic Number Protons Electron

Let’s review • Oxygen – Symbol? – Atomic Number? – Protons? – Electron Distribution? O 8 8 8 1 s 2 2 p 4 • Oxygen has 6 valence electrons. Episode 502

Electron Dot Diagrams • Atom’s symbol surrounded by dots to represent its valence electrons • Example • Oxygen • 6 valence electrons • Lithium • 1 valence electron Episode 502

Problem Set 1 Draw the Electron Dot Diagrams for: Magnesium Helium Krypton Aluminum Bromine Potassium Nitrogen Silicon Strontium Episode 502

Lewis Structure • Diagram representing the arrangement of valence electrons in a molecule • Most atoms need 8 valence electrons to become stable. The exceptions are H and He which need 2 valence electrons to be stable. Episode 502

Lewis Structure for H 2 • 2 electrons belonging to both atoms • Represented by a dash between the symbols H-H Shared pair Episode 502

Lewis Structure for Cl 2 • Each Cl atom has 7 valence electrons; giving a total of 14 valence electrons to work with. Shared pair Unshared pair Electrons belonging to only one atom Represented by 2 dots Episode 502

Lewis Structure for HCl H - Cl Episode 502

• When more than two atoms bond, you must determine which is central. • The central atom is: – Frequently carbon – Never hydrogen – Often atom with the smallest electronegativity • Lewis structure for CH 3 I • (There a total of 14 valence electrons to work with. ) H H C I H Episode 502

Problem Set 2 NH 3 CH 2 Cl 2 CH 3 OH (a little tricky) C 6 H 12 (Hint: The carbon atoms form a ring. ) Episode 502

Lewis structure of ethene, C 2 H 4 • (has total of 12 valence electrons) H H C C H H Type of bond Pairs of electrons shared Single bond Double bond Triple bond 1 2 3 Episode 502

Problem Set 3 CO 2 HCN CH 2 O C 2 HCl Episode 502

Polyatomic Ion • Covalently bonded groups of ions with a charge N = 5 electrons NO 3 -1 O = 3 x 6 electrons = 18 electrons -1 = 1 extra electron Has gained 1 electron to give a total of 24 valence electrons to work with [ O N O O -1 ] Episode 502

Problem Set 4 PO 4 -3 SO 4 -2 NH 4+1 CN-1 Episode 502