Monday, January 23, 2012

Characteristic properties of metallic and non-metallic elements

Metallic Elements
Nonmetallic elements
Distinguishing luster (shine) Non-lustrous, various colors
Malleable and ductile (flexible) as solids Brittle, hard or soft
Conduct heat and electricity Poor conductors
Metallic oxides are basic, ionic Nonmetallic oxides are acidic, compounds
Cations in aqueous solution Anions, oxyanions in aqueous solution
Metals
  • Most metals are malleable (can be pounded into thin sheets; a sugar cube chunk of gold can be pounded into a thin sheet which will cover a football field), and ductile (can be drawn out into a thin wire).
  • All are solids at room temp (except Mercury, which is a liquid)
  • Metals tend to have low ionization energies, and typically lose electrons (i.e. are oxidized) when they undergo chemical reactions
    • Alkali metals are always 1+ (lose the electron in s subshell)
    • Alkaline earth metals are always 2+ (lose both electrons in s subshell)
    • Transition metal ions do not follow an obvious pattern, 2+ is common, and 1+ and 3+ are also observed
  • Compounds of metals with non-metals tend to be ionic in nature
  • Most metal oxides are basic oxides; those that dissolve in water react to form metal hydroxides:
Metal oxide + water -> metal hydroxide
Na2O(s) + H2O(l) -> 2NaOH(aq)
CaO(s) + H2O(l) -> Ca(OH)2(aq)
  • Metal oxides exhibit their basic chemical nature by reacting with acids to form salts and water:
Metal oxide + acid -> salt + water
MgO(s) + HCl(aq) -> MgCl2(aq) + H2O(l)
NiO(s) + H2SO4(aq) -> NiSO4(aq) + H2O(l)

  • What is the chemical formula for aluminum oxide?
Al has 3+ charge, the oxide ion is O2-, thus Al2O3
  • Would you expect it to be solid, liquid or gas at room temp?
Oxides of metals are characteristically solid at room temp
  • Write the balanced chemical equation for the reaction of aluminum oxide with nitric acid:
Metal oxide + acid -> salt + water
Al2O3(s) + 6HNO3(aq) -> 2Al(NO3)3(aq) + 3H2O(l)

Nonmetals
  • Vary greatly in appearance
  • Non-lustrous
  • Poor conductors of heat and electricity
  • The melting points of non-metals are generally lower than metals
  • Seven non-metals exist under standard conditions as diatomic molecules:
    1. H2(g)
    2. N2(g)
    3. O2(g)
    4. F2(g)
    5. Cl2(g)
    6. Br2(l)
    7. I2(l) (volatile liquid - evaporates readily)
  • Nonmetals, when reacting with metals, tend to gain electrons (typically attaining noble gas electron configuration) and become anions:
Nonmetal + Metal -> Salt
3Br2(l) + 2Al(s) -> 2AlBr3(s)
  • Compounds composed entirely of nonmetals are molecular substances (not ionic)
  • Most nonmetal oxides are acidic oxides. Those that dissolve in water react to form acids:
Nonmetal oxide + water -> acid
CO2(g) + H2O(l) -> H2CO3(aq) [carbonic acid]
(carbonated water is slightly acidic)
  • Nonmetal oxides can combine with bases to form salts
Nonmetal oxide + base -> salt
CO2(g) + 2NaOH(aq) -> Na2CO3(aq) + H2O(l)
Metalloids
Properties intermediate between the metals and nonmetals.
Silicon for example appears lustrous, but is not malleable or ductile (it is brittle - a characteristic of some nonmetals). It is a much poorer conductor of heat and electricity than the metals. Metalloids are useful in the semiconductor industry.
Trends in Metallic and Nonmetallic Character
  • Metallic character is strongest for the elements in the leftmost part of the periodic table, and tends to decrease as we move to the right in any period (nonmetallic character increases with increasing ionization values)
  • Within any group of elements (columns), the metallic character increases from top to bottom (the ionization values generally decrease as we move down a group). This general trend is not necessarily observed with the transition metals.

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