Atoms, Molecules and Stoichiometry

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Syllabus Notes

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<p>Chemistry Syllabus Notes: Atoms, Molecules and Stoichiometry a) Relative atomic mass is the average mass of an atom of an element as compared to 1/12 the mass of an atom of the carbon-12 isotope. Relative isotopic mass is the mass of an atom of an isotope of an element as compared to 1/12 the mass of an atom of the carbon-12 isotope. Relative molecular mass is the average mass of a molecule of a compound as compared to 1/12 the mass of an atom of the carbon-12 isotope. Relative formula mass is the sum of the average atomic masses of all the atoms present in one formula unit; the smallest unit of an ionic compound represented in its formula, as compared to 1/12 the mass of an atom of the carbon-12 isotope. b) A mole is the unit for the amount of substance that is equal to 6.02 x 10 23 particles (atoms, molecules, ions or electrons) of the substance. c) The relative atomic mass of an element can be calculated from the relative abundances of its isotopes through:</p> <p>Where xn refers to the relative isotopic mass of an isotope of the element and a n refers to the corresponding abundance of the isotope. d) The empirical formula of a chemical compound is the simplest whole number ratio of atoms of each element present in a compound. The molecular formula of a compound is the number of each constituent atom in a compound.</p>

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