Chapter 6 Notes - Summary General Chemistry PDF

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Phoebe Zhang

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6. Ionic Bonds and Compounds 6-1. The Electrostatic Force That Binds Oppositely Charged Ions Together Is Called an Ionic Bond  When most ionic compounds dissolve in water, crystals break up into ions rather than neutral molecules  Movement of ions toward respective electrodes constitutes electric current through solution Properties Ionic compounds Covalent compounds Molecular structure Tend to form extended crystal Tend to exist as individual molecules lattices of alternating ions with shared electrons In solutions or liquid phase Form ions, good conductors of Do not form ions, poor conductors electricity of electricity Varies, typically low Melting point High (all are solids at 25 ℃ )  Aqueous solution of sucrose (table sugar), C12H22O11 (aq), contains neutral sucrose molecules, does not conduct electric current  Once sodium atom loses 3s electron, resultant configuration is relatively stable  Sodium & chloride ions have opposite charges, attract  Electrostatic force: the attraction or repulsion of different particles and materials based on their electrical charges.  Ionic bound  Octet rule: the tendency of main-group elements to form stable noble-gas-like ions  Metallic elements lose electrons to become positively charged ions called cations  Nonmetallic elements gain electrons to become negatively charged ions called anions 6-2. Chemical Formulas of Ionic Compounds Are Based on Ionic Charge 6-3. The Common Ionic Charges of Transition Metal Ions Can Be Understood in Terms of Electron Configurations  18-outer electron configuration  18-electron rule: the unusual stability of the ns2np6nd10  Metals that form 18-electron ions occur near ends of d transition series & charge on ions increases by one unit left to right  All subshells completely filled is relatively stable, two common ionic charges 6-4. The Ionic Charge of Transition Metal Ions with More Than One Common Ionic Charge Is Indicated by a Roman Numeral  Transition metals can form ions with more than one ionic charge  Indicate ionic charge of metal ions when naming compounds containing such metal  Older nomenclature o –ous ending to indicate the lower common ionic charge o –ic ending to indicate the higher common ionic charge 6-5. The Filling Order of Most Transition Metal Ions Is Regular  When electrons are lost from a neutral atom, the charge on the ion alters the order of the orbital energies such that in most transition metal ions, the energy of the 3d orbitals is less than that of the 4s orbital  Similar for 4d and 5s orbitals and 5d and 6s  Therefore, filling order of orbitals for majority of transition metal ions is regular  1s < 2s < 2p < 3s < 3p < 3d < 4s < 4p < 4d < 4f < …  Ground state electron configuration of nickel atom: [Ar]4s23d8  Singly charge nickel ion: [Ar]3d9 & not [Ar]4s23d7 or [Ar]4s13d8 6-6. Cations Are Smaller and Anions Are Larger Than Their Neutral Parent Atoms  Ionic radii  Average distance from nucleus of 3s electron in sodium atom is greater than that of 1s, 2s & 2p electrons because 3s electron is in n = 3 shell  Excess positive charge draws remaining electrons toward nucleus  Isoelectronic: having the same number of electrons

Phoebe Zhang

2

6-7. Coulomb’s Law Is Used to Calculate the Energy of an Ion Pair  Electron affinity: the change in energy of a neutral atom  Equilibrium ion-pair separation distance: the distance between the centers of an ionically bonded ion pair; deq  First electron affinity: EA1; is negative because energy is released  Second electron affinity: EA2; is positive because it requires energy to overcome the repulsion between the negatively charged ion and the electron  Coulomb’s law: state that the energy of interaction of two ions is directly proportional to the product of their electrical charges and is inversely proportional to the distance between their centers o

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Ecoulomb = k

Q1 Q2 d

o Q1 and Q2: charges of the two ions o D: the distance between the centers of the two ions o k: a proportionality constant Minus sign means that ions attract each other & energy is released when ions are brought together, energy of pair of ions is less than it is when ions are far from each other Erxn = I1 + EA1 + E3 = E1+2 + E3...