electro negativity : A measurement of how much an atom tends to steal
electrons from atoms that it's bonded to. Elements at the top right of the
periodic table (excluding the noble gases) are very electronegative while
atoms in the bottom left are not very electronegative (a.k.a. "electropositive")
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electropositive : When something is not at all electronegative. In fact, it
tends to lose electrons rather than to gain them. Elements that are
electropositive are generally to the left and bottom of the periodic table.
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empirical formula : A reduced molecular formula. If you have a molecular
formula and you can reduce all of the subscripts by some constant number,
the result is the empirical formula.
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emulsion : When very small drops of a liquid are suspended in another. An
example of an emulsion is salad dressing after you've shaken it up.
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enantiomers : molecules that are nonsuperimposable mirror images of each
other.
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endothermic : When a process absorbs energy (gets cold).
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endpoint : The point where you actually stop a titration, usually because an
indicator has changed color. This is different than the "equivalence point"
because the indicator might not change colors at the exact instant that the
solution is neutral.
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energy level : A possible level of energy that an electron can have in an atom.
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enthalpy : A measurement of the energy content of a system.
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entropy : A measurement of the randomness in a system.
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enzyme : A biological molecule that catalyzes reactions in living creatures.
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equilibrium : When the forward rate of a chemical reaction is the same as the
reverse rate. This only takes place in reversible reactions because these are
the only type of reaction in which the forward and backward reactions can both
take place.
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