Chem 161-2011 lecture 7, Chapter 5

Chem 161-2011 lecture 7, Chapter 5 - CHEMISTRY 161-2011...

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CHEMISTRY 161-2011 LECTURE 7 CHAPTER 5 IONIC AND COVALENT COMPOUNDS ANNOUNCEMENTS E-MAIL EXAMS Chem 161-2011 Lecture 6 1
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PLAN FOR TODAY : Finish chapter 4 Periodic Trends Compounds Lewis dot symbols Ionic compounds and bonding Chemical formula Lattice energy Naming ions and ionic compounds Formulas of ionic compounds Naming ionic compounds Covalent bonding and molecules Molecules Molecule Law of definite proportions Law of multiple proportions Diatomic molecule Homonuclear diatomic molecules Heteronuclear diatomic molecules Polyatomic molecules Molecular formulas Molecular formula Allotrope Structural formula Empirical formulas Naming molecular compounds Specifying numbers of atoms Compounds containing hydrogen Organic compounds Covalent bonding in ionic species Polyatomic ions Oxoanions Oxoacids Hydrates Familiar inorganic compounds Molecular and formula masses Percent composition of compounds Percent composition by mass Empirical formula mass Percent composition of compounds Molar mass Interconverting mass, moles and numbers of particles Determination of empirical fromula and molecular formula from percent composition Chem 161-2011 Lecture 6 2
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Chem 161-2011 Lecture 6 3 SMALLER ATOM SMALLER ION MORE ENDOTH. FIRST IONIZATION ENERGY MORE EXOTH. FIRST ELECTRON AFFINITY LESS METALLIC Some diagonal relationships exist, e.g., similar properties of B and Si PERIODIC TABLE AND PERIODIC PROPERTIES
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ET: Understanding what “effective nuclear charge” is. Discuss “shielding” effect. 4 FACTORS GOVERNING PERIODIC TABLE TRENDS EFFECTIVE NUCLEAR CHARGE 17 Cl=1s 2 2s 2 2p 6 3s 2 3p 5 Effective nuclear charge* = +7 17+ 17+ 7+ 7- 8- 2- 7- 8- 2- Valence electrons Core electrons Nuclear charge X X X *Burdge and Overby include the weaker shielding effect of the valence electrons, as well as the shielding effect of the core electrons, to determine the effective nuclear charge. Although they are correct, consideration of the effect of the valence electrons is virtually impossible to calculate, and is an unnecessary complication. I only include the core electron effect. Qualitatively, our results agree.
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FACTORS GOVERNING PE RIODIC TABLE TRENDS (1) Increasing valence principle shell number (with same [or weaker] effective nuclear charge) → less attraction of valence electrons to nucleus (2) Increasing effective nuclear charge (with same [or fewer] number of principal shells) → Greater attraction of valence electrons to nucleus. Isoelectronic series follows “Z” pattern for size of atoms/ions. (3) Increasing electrons in valence shell (with same number of principal shells and same effective nuclear charge) → Greater electron repulsion (4) Exceptions: Ionization energy and electron affinity o Nearest neighbor atoms due mainly to relative subshell stabilities.
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