Chapter 7: Ionic and Metallic Bonding Honors Chemistry Chapter 7: Ionic and Metallic Bonding
Ions Valence electrons “A” group: number of groups = number of valence electrons Transition metals: need more information: either Roman numeral designation of oxidation state, -ic or –ous if only two oxidation states (-ic is for larger #) Octet Rule: atoms either gain or lose electrons so as to reach the electron configuration of a noble gas Cations: loss of electrons to reach the noble gas configuration; typical of elements with 1, 2 or 3 valence electrons Anions: gain of electrons to reach the noble gas configuration; typical of elements with 5, 6, or 7 valence electrons Elements with 4 valence electrons typically bond covalently Elements with 8 valence electrons typically do not bond
Ionic bonds and ionic compounds Formation of ionic compounds Ionic bonds: # positive charges must equal # negative charges…development of appropriate subscripts for compounds comes from this…criss-cross should help arrive at correct number, assuming correct charge is listed (see previous slide!) Formula unit: the lowest number of ions in the correct whole number ratio…realization is that ionic compounds form network solids rather than simple molecules…consider illustration, pg. 195, of sodium chloride Properties of ionic compounds Crystalline solids, typically, as have higher MPs When molten or dissolved in water (if soluble), will conduct an electric current Coordination number: number of ions of opposite charge that surround an ion in a crystal (see page 198)
Bonding in Metals Realization that metals can be modeled as being in a sea of relatively mobile electrons Metallic bonds, then, are the bonds of these “flowing” electrons, creating some degree of attraction between atoms This also explains the characteristics we expect and see from metals Malleability Ductility Electrical/thermal conductivity Alloys Mixtures of two or more elements, at least one metal Like any hybrid, there are particular properties that are superior to the components