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Atom Definition
 smallest subdivision of matter that retains the chemical
characteristics of that particular material
 size of an atom: ~1 ten millionth of a millimetre (1x10-10 m)
Atom Components
 a central nucleus contains neutrons (neutral charge) and protons
(positive charge)
 neutron (0) = 1 AMU (Atomic Mass Unit)
 proton (+) = 1 AMU
 the "electron cloud" orbits the nucleus; electrons are confined to
"shells"
 electron (-) = negligible mass
 the structure of an atom invokes the analogy of a miniature solar
system where the sun represents the nucleus, and the rest of the solar
system represents the elctron cloud. The planetary orbits therefore
symbolize the shells within which one or more electrons may be
present. An important difference: the solar system is "flat"; electron
clouds are spherical.
 so why don't the negatively charged electrons and the positively
charged protons in the nucleus attract each other? Don't opposites
attract? Yes, but the electrostatic attraction between electrons and
protons is overcome by the high speed of the electrons whizzing
around the nucleus.
Atomic Mass and Number, Isotopes, and Ions
 atomic number = number of protons
 e.g., atomic number for carbon [C] is 6 because it has 6
protons in its nucleus
 atomic mass = number of protons and neutrons
 e.g., atomic mass for carbon [C] is 12 because it has 6
protons and 6 neutrons in its nucleus
 isotopes = variable number of neutrons
 e.g., "carbon 14" is an isotope of carbon that contains 2
extra neutrons in the nucleus -- its atomic mass is now 14
instead of 12
 ions = variable number of electrons; ions are charged particles
 e.g., C4+ is a carbon ion in which carbon has effectively
lost (by giving away or by sharing) four of its negatively
charged electrons and the proportion of electrons and
protons is no longer equal
 cation is a positively charged ion that lost electrons (+)
 anion is a negatively charged ion that gained electrons (-)
Compounds
 combination of one or more anions with one or more cations in a
specific ratio
 sum of the ion charges must equal 0 (in other words, the charge of
the negative ions must equal the charge of the positive ions -otherwise the compound would carry an electric charge and you
would get a shock when you touch it!)
 example: Na 1+ + Cl 1- => NaCl 0 (superscripts denote the
charge of the ion)
Minerals
Minerals (like everything else!) are made of atoms. The atoms are
bonded together to form compounds. In order to be defined as
"minerals", these chemical compounds must conform to strict "rules".
They must have:

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

formed naturally
a solid form
an inorganic origin
a specific composition (the composition of a mineral is defined by
the types of chemical elements present and their proportions)
 a characteristic crystal strucutre (i.e., the atoms are packed together
in an orderly pattern within the mineral)
 characteristic physical properties (crystal form, cleavage, colour,
hardness, solubility, density, lustre, streak (colour of powdered
mineral), magnetism)
See your class notes and textbook for further discussion.