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Lecture 20

CHEM1006 Lecture 20: Chem2_20

3 Pages
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Department
Chemistry
Course Code
CHEM1006
Professor
Reeves Valerie

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Lecture 20
Chemists use a variety of notations to describe and
summarize the atomic constituents of compounds.
These notations, which include empirical, molecular, and
structural formulas, use the chemical symbols for the
elements along with numeric values to describe atomic
composition.
Empirical formulas are the simplest form of notation.
They provide the lowest whole-number ratio between the
elements in a compound.
Unlike molecular formulas, they do not provide
information about the absolute number of atoms in a
single molecule of a compound.
The molecular formula for a compound is equal to, or a
whole-number multiple of, its empirical formula.
An empirical formula lacks any structural information
about the positioning or bonding of atoms in a molecule.
It can therefore describe a number of different
structures, or isomers, with varying physical properties.
For butane and isobutane, the empirical formula for both
molecules is C2H5, and they share the same molecular
formula, C4H10.
One structural representation for butane is
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Description
Lecture 20 Chemists use a variety of notations to describe and summarize the atomic constituents of compounds. These notations, which include empirical, molecular, and structural formulas, use the chemical symbols for the elements along with numeric values to describe atomic composition. Empirical formulas are the simplest form of notation. They provide the lowest whole-number ratio between the elements in a compound. Unlike molecular formulas, they do not provide information about the absolute number of atoms in a single molecule of a compound. The molecular formula for a compound is equal to, or a whole-number multiple of, its empirical formula. An empirical formula lacks any structural information about the positioning or bonding of atoms in a molecule. It can therefore describe a number of different structures, or isomers, with varying physical properties. For butane and isobutane, the empirical formula for both molecules is C2H5, and they share the same molecular formula, C4H10. One structural representation for butane isCH3CH2CH2CH3, while isobutane can be described using the structural formula3CH. Butane. Empirical formulas can be determined using mass composition data. A CHN analyzer can be used to find the mass fractions of carbon, hydrogen, oxygen, and other atoms for a sample of an unknown organic compound. Once the relative mass contributions of elements are known, this information can be converted into moles. Th
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