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