Lesson 2.1 Fundamental Chemical Laws
Suggested Readings:
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Zumdahl: Chapter 2 Sections 2.1, 2.2 & 2.3
Chapter 2 study cards 1, 2 & 3.
Essential Question: How have the fundamental chemical laws
impacted the study of chemistry?
Learning Objective:
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Summarize the fundamental chemical laws and theories.
Recall from the Chapter 2 study guide that AP questions are very rarely set
directly on the atomic principles and “laws”, but you are expected to know
and apply these in a broader context. For example, when you use
stoichiometry to determine the theoretical yield of a chemical reaction you are
applying the law of conservation of mass. When you write a chemical
formula, you are applying the law of definite proportions. Chemistry itself is
the application of the fundamental chemical laws. As you proceed through
this course, think about the various way in which chemistry follows the
fundamental laws outlined below.
Law of Conservation of Mass
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Antoine Lavoisier, 1774
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Carried out a bunch of experiments in which he weighed products
and reactants.
He discovered mass is neither created nor destroyed during a chemical
reaction. Rather, mass is conserved.
This seems pretty basic to us, but the idea of quantifying chemical
substances was innovative in the late 1700s.
Law of Definite Proportions
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Joseph Proust, 1799
AKA Proust's Law or the law of constant composition.
Pure chemical compounds always contain the same elements and
have the same percentage composition of each
element by mass.
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For example, water is always made of 11.1% hydrogen and 89.9%
oxygen.
According to Proust's law, every molecule of aspirin
will be the same!
Atomic Theory
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John Dalton, 1808
Although Dalton was not the first to suggest the existence of the atom,
he is given credit for atomic theory because he was first to formulate a
precise definition of the atom.
Atomic theory is said to mark the beginning of the modern era of
chemistry.
Dalton's hypothesis consisted of four parts that can be stated in a
variety of ways.
Here is one version
1. Elements are composed of extremely small particles called atoms.
2. All atoms of a given element are identical, having the same mass
and chemical properties. The atoms of one element are different
from the atoms of all other elements.
3. Compounds are composed of atoms of more than one element. A
given compound always has the same relative numbers and types
of atoms.
4. A chemical reaction involves only the separation, combination or
rearrangement of atoms; it does not result in their creation of
destruction.
Watch the following YouTube Video:
https://www.youtube.com/watch?v=wsYDL6EjV4k
Law of Multiple Proportions
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Atomic theory lead Dalton to propose the law of multiple proportions,
which follows from his third hypothesis.
According to the law, if two elements combine to form more than one
compound, the masses of one element that combine with a fixed mass
of the other element are in ratios of small whole numbers.
The illustration below illuminates this concept. Take a close look!
Many students have difficulty distinguishing the law of definite proportions
from the law of multiple proportions. This post may help you to understand the
difference. (click on the link for more information).