Crystal Chemistry

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Crystal Chemistry
2012-10-03 23:40:05
Crystal Chemistry

Crystal Chemistry
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  1. define the following
    Atomic number (Z)
    Mass number (A) +Atomic mass
    Atomic weight 
    • Z= number of protons, defines the chemical element
    • A= number of neutrons +protons
    • Atomic mass =mass of atom divided by 1/12 the mass of a C12 atom
    • Atomic weight =weighted average of the atomic masses of the isotopes
    • Isotopes - elements with same no of protons but diff no of protons
  2. What happens to atomic radius of elements down the group and across period?
    Atomic radius increases Down a group and Decreases across a period.
  3. What happens to ionic radius of elements down the group and across period?
    relative ionic radius increases for Anions as they gain more electons. but across the anion period, the anions decrease in radius due to having more protons to pull in the electons

    Cations however decrease in relative ionic radius, but ionic radius still overall still increases down a group because of increasing shells. across a period, Ionic radius decreases due to more electons being lost
  4. Define oxidation state
    also called Valence, refers to the charge of an ion. Radius of an ion is heavily controlled by their oxidation state

    Increasing positive charge, means smaller ionsbecause remaining electrons are held in more tightly and closely to the nucleus.
  5. Define electonegativity
    Low electronegativity
    High elecronegativity
    a measure of the tendency for an element to gain or lose electrons.

    • Low - loss of outer calence electrons to form cations
    • high - Gain of extra electrons to form an anion
  6. how many elemetns comprise the large majority of earths crust and which are they?
    O, Si, Al, Fe, Ca, Na, K, Mg

    almost  100% of earths crust
  7. Define Ionic bonding
    A chemical bond formed by the electrostatic attraction between positive and negative ions

    Na + Cl --> Na+ + Cl- --> NaCl

    • Charges of the two ions are balanced by the Born repulsion,
    • packing is symmetrical and systematic
  8. Define Covalent bonding 

    what determines strength of covalent bonds?
    A chemical bond formed by sharing of electrons between atoms ; occurs when the orbitals of the two toms overlap.

    -  strength is a function of degree to which orbitals of adjacent atoms overlap - more overlap = stronger bonds.

    E.g. DIAMOND C
  9. What is metallic bonding?
    A type of covalent bond in which valence electrons are delocalised and free to move around from to atom throughout the crystal structure; 

    - DO NOT involve matching specific orbitals on adjacent ations so bonds are relatively weak --> METALS ARE THUS SOFT AND MALLEABLE AND ONE CAN EASILY BE SUBSTITUTED FOR ANOTHER TO FORM AN ALLOY
  10. Define effective radius
    Distance between the centres of adjacent atoms or ions in thecrystals structure
  11. Electons
    -orbit the nucleus and are organised into discrete energy levels, what are these shells and subshells and how do they change in energy.
    • Shells (K,L,M,N)
    • Subshell (s, p,d, f)

    orbital energy increases with increasing number of shells.
  12. Show a representation of a covalent bond
  13. Show a representation of an ionic bond (halite)