Honors%20Chemistry

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Honors Chemistry

• Chapter 8 Periodicity

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8.1 The Periodic Table

• John Newlands (1864)
• Arrange elements by mass
• Properties repeat every 8th element
• Law of Octaves
• Ridiculed for musicalreference

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8.1 The Periodic Table

• Dmitri Mendeleev (1869)
• Periodic Law
• Grouped elements byrepeating properties
• Predicted properties of undiscovered elements
• Problem switched pairs of elements
• Moseley count by atomic , not by mass

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8.2 Periodic Classification

• Old vs. new numbering system
• Representative Elements (main group)
• Groups IA VIIA, Unfilled s or p sublevels
• Noble Gases
• Group VIIIA, Filled p sublevel
• Transition Metals
• B Groups, Unfilled d sublevel
• Lanthanides and Actinides
• Unfilled f sublevel

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8.2 Periodic Classification

• Valence Electrons
• Electrons in outermost shell
• Highest n quantum number reached
• Involved in chemical bonding
• Representing Free Elements
• Metals always use single atom (Na, Fe, Cu)
• Most nonmetals also monatomic (C, As, Kr)
• Sulfur actually S8, but we usually use just S
• Phosphorous exists as P4
• Diatomics H2, N2, O2, F2, Cl2, Br2, I2

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8.2 Electron Configurations of Ions

• Representative Elements
• Try to get ns2 np6 (isoelectronic with noble
  gas)
• Metals lose electrons (cations)
• Nonmetals gain electrons (anions)
• Find electron configurations of...
• K
• Al3
• S2-
• C4-
• Sn2

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8.2 Electron Configurations of Ions

• Transition Metals
• End with s2 dn
• Remove the higher-level s electrons first 2
• Remove ds one at a time until d5 or d0
• Often not isoelectronic with noble gas
• Predict oxidation states of...
• Fe
• V
• Cd
• Ag

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8.3 Effective Nuclear Charge

• Z of protons nuclear charge
• Decreases with distance from nucleus
• Decreased by shielding effect
• Zeff Z s
• s shielding constant
• s increases with intervening shells

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8.3 Atomic Radius

• Size of an atom
• Half distance between adjacent nuclei
• Radius increases down a group
• Caused by increasing number of shells
• Radius decreases across a period
• Caused by increased Z on the same shells
• Which is bigger Ca or Sr? Ca or Zn?

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8.3 Atomic Radius
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8.3 Ionic Radius

• Radius of a cation or anion
• Anion (negative charge) size increases
• More electron repulsion
• Cation (positive charge) size decreases
• Less electron repulsion
• Isoelectronic ions
• Size decreases with increasing positive charge
• Size increases with increasing negative charge
• Compare sizes of O2-, F-, Ne, Na, Mg2

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8.4 Ionization Energy

• Minimum energy needed to remove an electron from
  an atom in its ground state
• Measured in kJ/mol
• Measures how tightly electrons are held
• Multiple ionization energies
• increases across a period
• Increased nuclear force
• decreases down a group
• Increased dist. from nucleus

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8.4 Ionization Energy
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8.5 Electron Affinity

• Measure of the energy change when an atom gains
  an electron
• Measure of attraction for electrons
• Also measured in kJ/mol
• More difficult to measure than Eion
• Same trends as Eion
• increases across period
• decreases down group

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8.6 Periodicity of Chemical Properties

• Eion atoms attraction for its own e-
• EA atoms attraction for other e-
• Metals low attraction form cations
• Nonmetals high attraction form anions
• Diagonal relationships
• Similarities between pairs in different groups
• Likely caused by small size at the top of the
  group
• Similar charge densities in cations

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8.6 Properties Across a Period

• Need to compare similar compounds
• Use oxides for comparison
• Metal oxides
• Ionic, High melting/boiling point
• Basic
• Nonmetal oxides
• Molecular, Low melting/boiling
• Acidic
• Amphoteric
• both acidic and basic prop.