F321

• Created by: FreyaBee
• Created on: 05-12-12 09:42
• F321
• Atomic Masses
• Relative isotopic mass = mass of an istope compared with 1/12 mass of carbon-12
• Relative atomic mass (Ar) = The weighted mean mass of an atom of an element compared with 1/12 the mass of carbon-12
• Relative formulamass = weighted mean mass of a formula  unit compared with 1/12 Carbon-12
• Relative Molecular Mass (Mr) = Weighted mean mass of a molecule compared with the mass of 1/12 cabon-12
• Moles (n)
• The number of atoms per mole of the carbon-12 istotope
• 6.02 x 10^23 mol^-2
• Working out moles
• Gas
• |STP| n=V(in cm3)/22,400
• |RTP| n=V(in cm3)/24,000
• Equal volumes of gases at the same temp and pressure  = equal number of molecules
• Solid
• moles = mass/molecular mass
• n=m/M
• Amount of any substance containing as many particles as there are carbon atoms in 12g of carbon-12.
• Molar mass (M) = Mass per mole of a substance
• Found by adding together relative atomic masses
• Formulas
• Empirical formula
• Smallest whole number ratio of atoms of each element present in a compound
• Always used for compounds with giant structures
• Found by dividing by smallest value
• Molecular Formula
• Actual number of atoms of each element  in a molecule
• Molecules
• small group of atoms held together   by covalent bonds