Christopher Chui

1
Chemistry Chapter 9

• Christopher Chui

2
Early Attempts at Classification

• Dobereiner (1817) discovered groups of three
  elements with similar properties triad
• Triads are Ca, Ba, Sr Cl, I, Br S, Te, Se
• Newlands (1863) law of octaves was proposed to
  explain the repetition of similar properties that
  occurred with every 8th element when the elements
  were arranged in order of increasing atomic mass
• Mendeleev (1869) correctly predicted properties
  and masses of unknown elements
• Mendeleev believed that the properties of the
  elements were periodic functions of their atomic
  masses

3
Modern Periodic Law

• The modern periodic law states that the
  properties of the elements are a periodic
  function of their atomic numbers (Moseley 1913)
• Elements with similar electron configurations are
  listed in the same column
• Electron capacity s2, p6, d10, f14
• The transition elements fill columns 3-12

4
Lanthanoids and Actinoids

• Electrons are added to the 4f sublevel in the
  lanthanoid series
• Electrons are added to the 5f sublevel in the
  actinoid series
• Periods are horizontal rows of elements
• Groups are vertical columns of elements
• Eight electrons in the outer energy level of an
  atom represent a stable arrangement
• Helium, with 2 electrons, is included in the
  octet rule
• The periodic table can be used to determine the
  electron configuration of an element

5
Electronic Configurations

• Atoms in the same period have the same principal
  quantum number, n
• Full or half-full sublevels are particularly
  stable
• Some deviations from the arrow diagram are
  periodic and thus easily explained
• Groups 1 and 2 contain the most active metals
• Metals generally have fewer electrons in the
  outer level than non-metals

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Groups of elements families

• Gp1 alkali metals Gp2 alkaline earth metals
  Gp3-Gp12 transition metals Gp13-15 semimetals
  and metals Gp16 chalcogens Gp17 halogens
  Gp18 noble gases
• Lanthanoids and actinoids are separate classes