notes: ionic and metallic bonding (ch 7). valence electrons: recall… ● valence electrons: the e-...

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: 1s2 2s2 2p6 3s1

Na+:

CATIONS:

● Na: 1s2 2s2 2p6 3s1

● Na+:

● Mg: 1s2 2s2 2p6 3s2

● Mg2+:

CATIONS:

● Na: 1s2 2s2 2p6 3s1

● Na+: 1s2 2s2 2p6

● Mg: 1s2 2s2 2p6 3s2

● Mg2+: 1s2 2s2 2p6

OCTET RULE:

● Atoms of NONMETALS obey this rule by gaining electrons.

Cl: 1s2 2s2 2p6 3s2 3p5

Cl-:

ANIONS:

● Cl: 1s2 2s2 2p6 3s2 3p5

● Cl-:

● O:1s2 2s2 2p4

● O2-:

ANIONS:

● Cl: 1s2 2s2 2p6 3s2 3p5

● Cl-: 1s2 2s2 2p6 3s2 3p6

● O: 1s2 2s2 2p4

● O2-: 1s2 2s2 2p6

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

Al3+ and Br- form AlBr3

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:

Na Cl

Al Br

K O

Mg N

K P

Na+Cl- = NaCl

Al3+Br- = AlBr3

K+O2- = K2O

Mg2+N3- = Mg3N2

K+P3- = K3P

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