Chemical Bonding I: Basic Concepts Chapter 9 Semester 1/2015

9.1 LEWIS DOT SYMBOLS 9.2 THE IONIC BOND 9.4 THE COVALENT BOND

Valence electrons..total electrons in the outer most shell which participate in chemical bonding. Example: 3 Li … 1s 2, 2s 1 valence e - = 1 Li * 4 Be..1s 2, 2s 2 valence e - = 2

Na + F Na + F - The Ionic Bond 1s 2,2s 2 2p 6,3s 1 1s 2,2s 2 2p 5 1s 2,2s 2 2p 6 1s 2 2s 2 2p 6 [Ne] Na Na + + e - e - + FF - F - Na + + Na + F - (i)Chemical bond exists between metal and non-metal. (ii)Metal loses electron to become cation (stable, inert electron structure) (iii)Non-metal gains electron to become anion (stable, inert electron structure ) (iv)Strong attraction between cation and anion produces ionic bond.

A covalent bond is a chemical bond in which two or more electrons are shared by two Non-metal atoms. Why should two atoms share electrons? FF + 7e - FF 8e - F F F F Lewis structure of F 2 lone pairs single covalent bond

8e - H H O ++ O HH O HHor 2e - Lewis structure of water Double bond – two atoms share two pairs of electrons single covalent bonds O C O or O C O 8e - double bonds Triple bond – two atoms share three pairs of electrons N N 8e - N N triple bond or