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Unit 7

Chapter Overview
During this unit, students develop an understanding of Avogadro’s number and how to apply it to atoms, formula units, and molecules.  The concepts of mole and molar mass of substances are introduced by example and visualization.  Avogadro’s number and the molar mass are then used in calculations.  Students design and implement a descriptive investigation to determine the cost of an atom of an element.  Students also implement a comparative investigation to measure, calculate, and then use percent composition and molar mass to derive empirical and a molecular formulas.

Main Ideas
The mole is a fundamental SI unit in science.
A mole of anything contains Avogadro’s number of representative particles (atoms, molecules, ions, formula units).
An empirical formula gives the relative numbers of atoms of each element found in a chemical compound.
Percent composition is the percentage by mass of each element in a given compound.
A molecular formula for a compound is a whole number multiple of its empirical formula.

Avogadro’s Number/Constantthe number of representative particles in a mole of a substance 6.02x1023
Molecular Formulaa whole number multiple of the empirical formula
Empirical Formulathe simplest ratio of the different elements in a given compound
Mole Conceptthe idea that the number of particles and mass of a substance can be calculated using the SI unit mole
Molar Massthe mass in grams of a mole of a substance
Mole – the mass of substance containing the same number of fundamental units as there are in atoms in exactly 12.000g of 12C
Percent Composition – percentage by mass of each element in a compound
Atomic Mass – average mass of an element
Atomic Mass Unit (AMU) – average of the proton rest mass and the neutron rest mass
Formula Mass – the sum of the atomic weights of the atoms in the empirical formula of the compound


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