ch 2 AP notes Unit 1 Fundamentals.notebook

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• LO 1.1 The student can justify the observation that the ratio of the masses of the constituent elements in any pure sample of that compound is always identical on the basis of the atomic molecular theory.

• LO 1.17 The student is able to express the law of conservation of mass quantitatively and qualitatively using symbolic representations and particulate drawings.

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Reactants ­­­­­­­> ProductsMass of Reactants = Mass of Products

1. Law of conservation of mass (Lavoisier):

Mass is neither created nor destroyed in a chemical reaction.

3 Important Laws

Note that the hydrogen and oxygen atoms simply rearrange themselves but are not destroyed. Thereofore mass is conserved.

ch 2 AP notes Unit 1 Fundamentals.notebook

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2. Law of definite proportion (Proust 1758‐1826):A given compound always contains exactly the same proportion of elements by mass.

( The principle of the constant composition of compounds­ origially called "Proust's law".)

Example: Proust found that the substance copper carbonate is always 5.3 parts copper to 4 parts oxygen to 1 part carbon (by mass).

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3. 1808­ John Dalton stated the Law of Multiple Proportions

> When two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers.

Provided evidence that atoms exist

ch 2 AP notes Unit 1 Fundamentals.notebook

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Law of Multiple Proprotions:

Dalton considered compounds of carbon and oxygen and found:

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ch 2 AP notes Unit 1 Fundamentals.notebook

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ch 2 AP notes Unit 1 Fundamentals.notebook

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Exercise 2.1

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NO

NO

NO = 1

11= =2 1

2

ch 2 AP notes Unit 1 Fundamentals.notebook

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NO

NO

NO = 1

11= =2 1

2

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Example of Multiple proportions

do POGIL after this

Two elements, R and Q, combine to form two binary compounds. In the first compound, 14.0 g of R combines with 3.00g of Q. In the 2nd, 7.00g of R combines with 4.50 g of Q. Show that these data are in accord with the law of multiple proportions. If the formula of the first compound is RQ, what is the formula of the second?

RQ3

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ch 2 AP notes Unit 1 Fundamentals.notebook

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ch 2 AP notes Unit 1 Fundamentals.notebook

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Electrons are responsible for bonding and chemical reactivity.

Chemical bonds­ forces that hold atoms togetherCovalent bonds­ atoms share electrons and make molecules

(independent units); H2, CO2 are examplesMolecule­ smallest unit of a compound that retains the chem.

characteristics of the compound; characteristics of constituent elements are lost

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Lab Experiment # 4 Determination of a Chemical Formula

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