NOTES: Ionic and Metallic Bonding (CH 7)

Valence Electrons: RECALL… ● Valence Electrons: The e- in the highest occupied energy level of an element’s atoms.

Valence Electrons: ● Also, recall…the number of valence electrons for a representative element is equal to the group number of that element Examples: ● Group 1 elements (Na, K, Li, H): 1 valence e-. ● Group 2 elements (Mg, Ca, Be): 2 valence e-. ● Group 17 (7A) elements (Cl, F, Br): 7 valence e-.

OCTET RULE: and RECALL… ● Octet rule: atoms react by changing the number of electrons so as to acquire the stable electron structure of a noble gas.

OCTET RULE: ● Atoms of METALS obey this rule by losing electrons. Na: 1s 2 2s 2 2p 6 3s 1 Na + :

CATIONS: ● Na: 1s 2 2s 2 2p 6 3s 1 ● Na + : ● Mg: 1s 2 2s 2 2p 6 3s 2 ● Mg 2+ :

CATIONS: ● Na: 1s 2 2s 2 2p 6 3s 1 ● Na + : 1s 2 2s 2 2p 6 ● Mg: 1s 2 2s 2 2p 6 3s 2 ● Mg 2+ : 1s 2 2s 2 2p 6

OCTET RULE: ● Atoms of NONMETALS obey this rule by gaining electrons. Cl: 1s 2 2s 2 2p 6 3s 2 3p 5 Cl - :

ANIONS: ● Cl: 1s 2 2s 2 2p 6 3s 2 3p 5 ● Cl - : ● O:1s 2 2s 2 2p 4 ● O 2- :

ANIONS: ● Cl: 1s 2 2s 2 2p 6 3s 2 3p 5 ● Cl - : 1s 2 2s 2 2p 6 3s 2 3p 6 ● O: 1s 2 2s 2 2p 4 ● O 2- : 1s 2 2s 2 2p 6

Which elements form ionic compounds and which elements form covalent (molecular) compounds?? General Rule of Thumb: metal + nonmetal = IONIC metal + polyatomic anion = IONIC polyatomic cation + anion = IONIC nonmetal + nonmetal(s) = COVALENT

Why are ionic compounds so stable? ● IONIC BONDS: -metal plus a nonmetal -cations plus anions -opposite charges attract ● Examples:  Na + and Cl - form NaCl  Al 3+ and Br - form AlBr 3

IONIC BONDS: ● Anions and cations have opposite charges ● Ionic compounds are electrically neutral groups of ions joined together by electrostatic forces. (also known as salts)  the positive charges of the cations must EQUAL the negative charges of the anions.  we can use electron dot structures to predict the ratios in which different cations and anions will combine.

Examples of Ionic Bonds: NaCl AlBr K O MgN KP Na + Cl - = NaCl Al 3+ Br - = AlBr 3 K + O 2- = K 2 O Mg 2+ N 3- = Mg 3 N 2 K + P 3- = K 3 P

Properties of Ionic Compounds ● must contain an ionic bond ● crystalline solids at room temperature ● ions are arranged in repeating 3-D patterns ● high melting point ● melted or dissolved in water they conduct electricity

Metallic Bonds: ● METALS: made up of closely packed cations surrounded by mobile valence electrons

Metallic Bonds: ● METALLIC BOND = attraction of free- floating (mobile) valence electrons for the positively charged metal ions (sea of electrons around the cations) ● Explains properties of conductivity of electricity, malleability, and ductility

Metallic Properties: ● CONDUCTIVE: can conduct electricity because electrons can flow freely in them ● DUCTILE: can be drawn into wires ● MALLEABLE: can be hammered or forced into different shapes WHY??...the sea of free-flowing electrons insulates the metal cations from each other so they slide easily past one another.

ALLOYS: ● most metallic items we use every day are not pure metals…they are ALLOYS. ● ALLOYS: mixtures composed of 2 or more elements, at least one of which is a metal. ● prepared by melting a mixture of the ingredients together and then cooling

ALLOYS: Examples: ● BRASS=Cu + Zn ● STERLING SILVER =Ag + Cu ● BRONZE=Cu + Sn ● CAST IRON=Fe + C ● STAINLESS STEEL=Fe, Cr, C, Ni ● SURGICAL STEEL=Fe, Cr, Ni, Mo