Atoms, molecules and stiochiometry

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  • Created by: portia
  • Created on: 15-08-17 14:28
Stoichiometry
The mole ratio in which reactants combine together, with the mole ratio in which the products are formed is known as the stoichiometry of the reaction
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Empirical formula
Gives the simplest whole number ratio of different atoms present in a molecule
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Molecular formula
Gives the actual number of atoms present in one molecule
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Relative atomic mass, Ar
The relative atomic mass of an element is the weighted average of the masses of its isotopes on a scale on which a carbon-12 atom has a mass of exactly 12 units.
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Relative molecular mass, Mr
Mr of an element or compound is the mass of one molecule of the element or compound compared with the mass of an atom of carbon-12 which is given a mass of exactly 12
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Relative formula mass, Mr
Mr of an ionic compound is the mass of one formula unit of the compound compared with the mass of an atom of carbon-12 which is given a mass of exactly 12
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Relative isotopic mass, Ar
relative isotopic mass of a single isotope is the mass of an atom of this isotope compared with the mass of an atom of carbon -12 which is given a mass of exactly 12
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Why masses are compared to Carbon -12
The mass of an atom is incredibly small, and it doesn't make sense to use standard units like grams to measure it. Instead masses are measured on a scale based on the mass of an atom of the 12C isotope.
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Why is it the 'weighted' average mass
A "weighted average" allows for the fact that there won't be equal amounts of the various isotopes. (eg. if there are more of the lighter isotope - the "weighted" average ought to be closer to that.
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A mole
A mole of substance is the amount of that substance that contains 6.02 x10^24 of stated elementary units
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Other cards in this set

Card 2

Front

Gives the simplest whole number ratio of different atoms present in a molecule

Back

Empirical formula

Card 3

Front

Gives the actual number of atoms present in one molecule

Back

Preview of the back of card 3

Card 4

Front

The relative atomic mass of an element is the weighted average of the masses of its isotopes on a scale on which a carbon-12 atom has a mass of exactly 12 units.

Back

Preview of the back of card 4

Card 5

Front

Mr of an element or compound is the mass of one molecule of the element or compound compared with the mass of an atom of carbon-12 which is given a mass of exactly 12

Back

Preview of the back of card 5
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