Holding Atoms Together Chemical Bonding Holding Atoms Together

Today’s Objective: To be able to distinguish between the three types of bonds: ionic, covalent and metallic.

What we know about valence electrons and ions... Atoms are most stable (least reactive) when they have a valence shell which is full of electrons (e-). Think about the unreactive Noble Gases. ← Full octets → 8 valence e- Atoms frequently gain or lose e- to get a full valence shell and become ions. Losing e- creates + cations. Gaining e- creates - anions. Metals tend to lose electrons to gain a full valence shell, becoming cations. Nonmetals tend to gain electrons to fill their valence shell, becoming anions.

3 Types of Chemical Bonding Metal (+) and nonmetal (-) = Ionic Bond. e- are transferred from the metal to the nonmetal. Nonmetal and nonmetal = Covalent Bond. ←Note: No ions here!!! e- are shared between their valence shell. Atoms co-operate with their valence e-. They are co-valent. Metal and metal = Metallic Bond. Crazy Hot Potato leads to “sea of electrons.”

Identify the following compounds as either ionic or covalent. CCl4 = K3P = CuBr2 = SeO2 = Covalent Ionic Ionic Covalent

Polyatomic Ions Nitrate = NO31- Phosphate = PO43- Carbonate = CO32- Compounds which contain polyatomic ions have both covalent and ionic bonds. The six polyatomic ions (that you need to know for sixth grade)... Nitrate = NO31- Phosphate = PO43- Carbonate = CO32- Hydroxide = OH1- Sulfate = SO42- Ammonium = NH41+ (the only + one)

Properties of Covalent Compounds Covalent Compounds tend to… Form molecules (ionic compounds don’t) Have low melting points Be soft Be poor conductors of heat and electricity We say that they “tend” to be but there are many exceptions. Diamonds are very hard and have high melting points but are covalently bonded.

Properties of Ionic Compounds Ionic compounds tend to… Have high melting points (usually more than 1000 oF) Be good conductors of heat and electricity only as liquids and aqueous solutions Because ions are free to move around when they are melted and dissolved in H2O. Be brittle as solids Form crystal lattices