Cheatography
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Chemistry for first year of engineering
This is a draft cheat sheet. It is a work in progress and is not finished yet.
DEFINITION
Ionic bonding occurs between a metal and a non metal ion with the electrostatic attraction between the ions. The electron will leave the low electronegative metal and move to the high electronegative non-metal. |
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Characteristics
electrons placed inside the atoms |
strong electrostatic bonds |
no directional preference |
high melting and boiling points |
soluble in polar solvents (water, alcohols, ...) |
WHY?
BECAUSE OF LATTICE ENERGY
it is the enthalpy of formation of the ionic compound from gaseous ions, the measurement of the bonds' strength
Type of ionic interactions
electrostatic (main intercation) |
repulsive (between the electrons) |
repulsive (between the nuclei) |
Born-Haber Cycle
Lattice energy cannot be easily obtained experimentally |
Thus , we apply the Hess Law to realize indirect calculations |
standard enthalpy of formation |
ΔHf |
enthalpy of sublimation |
ΔHs=S |
enthalpy of dissociation |
ΔHd=D |
ionization energy (take an electron) |
ΔHi=I |
electron affinity (add an electron) |
ΔHEA=EA |
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Ionic Liquids (IL)
Salts in liquid state at room temperature made of ions |
Possible when the ionic charges aren't too high and the distance is large enough |
Useful properties |
-non volatile |
-remain in liquid state up to 400ºC |
-non flammable |
-good solvents for reactions |
-reduced volume |
-easy reuse |
Ionic Conductors (Superconductors)
They are solid state ion conductors used primarly in solid oxide fuel cells. |
They conduct electricity due to the movementof the ions through the voids. |
An example would be yttria-stabilized zirconia (YSZ)
Ionic Solids
Physical behaviour |
-HARD(NESS) |
related with the attractive cohesion force in the ionic structure. This property is related with the absolute value of the lattice energy (dir4ectly to the charge of ions, inversely to their size) |
-RIGID |
strog attractive forces hold ions in specific positions |
-BRITTLE |
when enough dorce is applied, ions of similar charge are brought next to eachother, and repulsions between them crack the sample |
ELECTRIC CONDUCTIVITY |
-solid state |
insulators (the valence electrons aren't mobile and the ions are in fixed positions)) |
-when molten |
electricity conductor (ions are mobile) |
-when dissolved in polar solvents |
electricity conductor (ions are mobile) |
SOLUBILITY |
ΔHsolution=-U+ΔHsolvation |
the higher the lattice energy of a salt, the less soluble it is |
MELTING AND BOILING POINTS |
-high melting point |
freeing ions from their positions require large amount of energy |
-much higher boiling points |
(the higher U is, the higher its boiling/melting point is) |
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