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Effective Nuclear Charge, Atomic Size

periodic table development - ordered according to atomic mass by Mendeleev/Meyer  

  • Mendeleev got majority of credit for advancing his ideas more vigorously and predicting the existence of substances yet to be discovered
  • Henry Moseley - arranged atoms by atomic number instead of atomic mass, solved the problems in the original periodic table

effective nuclear charge - electric field created by nucleus and surrounding electron density  

  • uses average environment created by nucleus/electrons
  • Zeff = Z - S
    • Z = number of protons in the nucleus
    • S = average number of core electrons
  • inner electrons shield outer electrons from the nucleus' charge
  • charge increases as you move across any row/period of the periodic table
    • Z increases as S stays the same, so Zeff increases
  • charge increases only slightly as you move down a column/family
    • larger electron cores less able to shield outer electrons than smaller cores

atomic radii - nonbonding/bonding radius  

  • nonbonding radii (van der Waals radii) - radius of atoms not in molecules
  • bonding radii (covalent radii) - radius of atoms in bonds
    • slightly shorter than nonbonding radii
  • increases as you move down column/family
    • outer electrons get farther from nucleus as principal quantum number increases
  • decreases as you move left to right across a row/period
    • as Zeff increases, outer electrons get pulled in more
  • ionic radii - depends on charge
    • cations - smaller than neutral atoms
    • anions - larger than neutral atoms
  • isoelectronic series - series of ions w/ same number of electrons, different number of protons
    • radius decreases as nuclear charge increases
Subject: 
Chemistry
Subject X2: 
Chemistry

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