Principles of Inorganic Geochemistry
These summary notes are based largely on Faure (1998), Chapters 6-8.
The Periodic Table
Periodic Law (Mendeleev): The physical and chemical properties of elements vary in
periodic fashion.
Mendeleev (1869) and Meyer (1870) recognized regular, “periodic” patterns among
elements with sequentially higher atomic weights and valences.
Mendeleev (1871) predicted the existence of the element Germanium which was later
discovered in 1886. He reordered Meyerʼs periodic table to leave a gap for Ge.
Mendeleev arranged elements in increasing atomic weight in successive sequences.
Elements with similar properties were arranged in columns.
The modern periodic table:
Periodic Properties
Atomic Radii
increase down a group (column)
decrease across a period (row)
" (increased nuclear charge draws electrons closer)
Ionization energy
energy required to remove the most loosely bound electrons from an isolated
gaseous atom to forma cation [1st ionization energy, 2nd ionization energy…]
measures how tightly electrons are bound to atoms
increases across a period (row)
Ionization Energy
Behavior
Bonding
low
donate electrons
form ionic compounds as cations
medium
share electrons
form covalent compounds
high
accept electrons
form ionic compounds as anions
Ionic Radii
(+) cations are smaller than the neutral atom
" because nucleus pulls electrons in more tightly
(-) anions are larger than the neutral atom
" because nuclear charge canʼt hold excess electrons as tightly
Electronegativity
relative tendency of an atom to attract electrons to itself when combined with
" another atom
electronegativity scale: 0 to 4 with F being the most electronegative (4)
varies from least in lower left of periodic table to greatest in upper right (aside from
" the noble gases
increases across a period (row)
the greater the electronegativity difference between two atoms, the greater the ionic
" character of the bond between them
Valences = Oxidation States
the number of electrons preferentially lost (to form cations) or gained (to form anion)
forming an ionic compound
Bonding
Ionic Bonding - transfer of electrons from cation to anion
Covalent Bonding - sharing of electron pairs
the greater the electronegativity difference between two atoms, the greater the ionic
character of the bond between them
elements from the same areas of the periodic table form covalent compound with one
another; elements from opposite sides of the periodic table form ionic compounds
Ionic Compounds
Covalent Compounds
high melting point solids because strong gases, liquid, low melting point solids
electrostatic attraction
most are soluble in polar solvents, e.g.,
H 2O
most are insoluble in polar solvents
most are insoluble in non-polar solvents
most are soluble in polar solvents, e.g.,
benzene
molten compounds conduct electricity
because they contain ions
liquid or molten compounds do not
conduct
aqueous solutions conduct because
they contain ions
aqueous solutions are poor conductors
because they donʼt contain ions
Electronegativity Difference
1)" The difference in electronegativity predicts the percent ionic or covalent character of
a bond
Electronegativity Difference
Ionic Character
Covalent Character
0.1
0.5%
99.5%
1.7
51%
49%
3.2
92%
8%
2)" The atom with the larger electronegativity attracts the electrons of the lower
electronegativity atom to itself
e.g., the H - O bond in H2O"
" electronegativity difference = 3.5 - 1.2 = 1.3
" ~60% covalent
" the oxygen nucleus draws hydrogensʼ electrons to it