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Chapter 3

Terms in this set (14)

12C
assigned a mass of exactly 12 atomic mass units
natural carbon is a mixture of isotopes, the atomic mass used for carbon is an average value based on its isotopic composition
Mass spectrometer
comparing the masses of atoms
atoms or molecules are passed into a beam of high-speed electrons, knock electrons off the atoms or molecules being analyzed and change them into positive ions, an applied electrical field accelerates these ions through a magnetic field, which deflects the paths of the ions
the amount of path deflection (causes ions to separate) for each ion depends on its mass, most massive are deflected in the smallest amount
Elemental mass
average value based on the isotopic composition of the naturally occuring element
mole
the number equal to the number of carbon atoms in exactly 12 grams of pure 12 C, a sample of a natural element with a mass equal to the element's atomic mass expressed in grams contains 1 mole of atoms
Avogadro's number
6.022 x 10^23 (in terms of atoms [amu]) and it also equals 1 gram of C
one mole of something consists of 6.022 x 10^23 units of that substance
To compute mass in grams
multiply the amu by the amount of atoms, take that number and divide it by Avogadro's number to get the answer in g
To compute molecules and atoms
first compute the molar mass of the sample, then determine the number of moles of the sample in a given number by dividing the given number by the molar mass to end in moles, multiply the moles by Avogadro's number to end in molecules

to determine a particular amount of elemental atoms, multiple the molecules by the amount of atoms to get atoms
Molar mass
the mass in grams of 1 mole of a compound, obtained by summing the masses of the component atoms
Percent composition of compounds
find the molar mass of a substance, then you are able to find the mass percent by placing the desired molecular mass over the initial molar mass then multiply it by 100%
Determining the formula of a compound
often determined by taking a weighted sample of the compound and either decomposing it into its component elements or reacting it with oxygen to produce substances such as CO2, H2O, and N2, which are collected and weighed
Combustion device
used to analyze substances for carbon and hydrogen, the sample is burned in the presence of excess oxygen, which converts all of its carbon to CO2 and all of its hydrogen to water.
their amounts are determined by measuring the increase in weights of the absorbents (the mass of each type is resulted which aides in determining the mass percent)
Empirical formula
the simplest whole-number ratio of the various types of atoms in a compound
Molecular formula
the exact formula of the molecule involved,
the molar mass and the percentages of each element present can be used to compute the moles of each element present in one mole of the compound
Chemical change
involves reorganization of the atoms in one or more substances, chemical equation has reactants and products.
bonds have been broken and new ones have formed
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