Chemical Bonding

Chemical Bond The forces that hold groups of atoms together and make them function as a unit Bonding involves only the valence electrons Electrons are transferred or shared to give each atom a noble gas configuration (stable octet) This is known as the octet rule There are 2 types of bonds: Ionic: Transfer of electrons from a metal and to a nonmetal Covalent: Sharing of electrons between 2 nonmetals

Lewis Diagrams Valence electrons involved in bonding can be represented by Lewis dot diagrams A chemical symbol represents the nucleus and the core electrons (not involved in bonding). Dots around the symbol represent valence electrons.

Drawing Lewis Diagrams Write the element symbol. Draw dots, one for each valence electron Dots should be spread over 4 sides It does not matter what side the dots are placed, but do not start to pair dots until there is one on each side The number of valence electrons is equal to the group number (for groups 1-3, 14-18), with one exception. Which element is it? Cl

Lewis diagrams for the first 20 elements

Ionic Bonding Metals Nonmetals Electron donors Donate their valence electrons to become a positive ion (cation) Nonmetals Electron acceptors Accept valence electrons to become a negative ion (anion)

Ionic Bonding

Ionic Bonding The two oppositely charged ions are attracted to each other by a force called an ionic bond

Properties of Ionic Compounds Structure: Crystalline solids Melting point: Generally high Boiling Point: Electrical Conductivity: Excellent conductors, molten and aqueous Solubility in water: Generally soluble

NaCl Crystal Lattice Ionic compounds form solids at SATP. Ionic compounds organize in a characteristic crystal lattice of alternating positive and negative ions. All lattices are arranged so that each ion has the greatest possible number of oppositely charged ions close by, while keeping similarly charged ions as far away as possible

Representing Ionic Compounds Lewis Diagrams Formation of sodium chloride: Cl · · · ® Na+ [ ] Cl · · Na · +

Lewis Structures for Ionic Compounds Ba • O •• •• O Ba 2+ 2- Ba and O BaO Mg • Cl •• •• Cl Mg 2+ - 2 Mg and Cl Binary ionic compounds. Note the types of arrows used to move electrons – fishhooks for single e-. Write the Lewis symbol for each atom Determine how many e- each atom must gain or lose. Use multiples of one or both ions to balance the number of electrons. MgCl2

Practice Problems p. 68 #1,4 p. 71 #1-5 p. 73 #8-13