Two Or More Atoms Join Together to Form a Stable Group

Chapter 3 Chemical Bonding Ionic Bonds

Bonding . Two or more atoms join together to form a stable group. . There are several types of forces (BONDS) which hold the atoms together in these groups. . IONIC (ionic compounds) . COVALENT (molecular compounds) . METALLIC (pure elements or homogeneous mixtures) . WEAK INTERMOLECULAR (ie.: the forces that hold water molecules together)

Differences in properties . Ionic Compounds . High melting point . Conduct electricity when molten or dissolved in water . Molecular Compounds . Low melting point . Does NOT conduct electricity when molten or dissolved in water.

What is an Ion? . An ion is an atom which has “lost” or “gained” one or more electrons, thus obtaining a “net” positive or negative charge. . Cations vs. Anions

Valence Electrons . Valence Electrons are the electrons in the Outermost Energy Shell. . The number of valence electrons matches the group number for the representative elements (s & p). . Transition (d) and Inner-transition (f) elements typically have “2” valence electrons. . However, some of their “outer ‘d’” electrons may participate in bonding.

Electron Dot Structures for Representative Elements Octet Rule . Atoms will attempt to gain or lose electrons to attain the same electron configuration as a Noble Gas. . Noble Gases have 8 valence electrons (except Helium)

Monatomic Ions vs. Polyatomic Ions . Monatomic IONS are comprised of only ONE element. . Ex. Na+, Cl-, Al3+, O2-, etc. . Polyatomic IONS are comprised of two or more elements. + - 2- 2- . NH4 , NO3 , SO4 , CO3 , etc.

Ionic Compounds Ionic Compounds are typically Crystalline in Form Ionic compounds occur when cations and anions bond together. . These ions join together because of electrostatic attractions between + & -. . Remember, cations are usually metallic elements (or “ammonium”) and - -2 -2 -2 anions are usually nonmetallic elements (or MnO4 , CrO4 , Cr2O7 , MoO4 .

Which part of the ionic compound is responsible for the typical physical properties?

Sodium chloride Why NaCl? Reactions of Ionic Compounds (an important example) . Tooth Enamel Demineralization

2+ 3- - Ca10(PO4)6(OH)2 <==> 10Ca + 6PO4 + 2OH

Predicting formulas using the Periodic Table and valence electrons • Metal atoms LOSE valence electrons to form cations • Nonmetal atoms GAIN valence electrons to form anions • Na (1 v.e-) --> Na+ (looks like neon) • Cl (7 v.e-) --> Cl- (looks like argon) • All ionic compounds have a net neutral charge, so the total positive charge must balance the total negative charge.

Naming Ionic Compounds