law of constant composition

(also, law of definite proportions) all samples of a pure compound contain the same elements in the same proportions by mass

law of definite proportions

(also, law of constant composition) all samples of a pure compound contain the same elements in the same proportions by mass

law of multiple proportions

when two elements react to form more than one compound, a fixed mass of one element will react with masses of the other element in a ratio of small whole numbers

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Chemistry 2e · 2.1 Early Ideas in Atomic Theory

Early Ideas in Atomic Theory: practice problems

2 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 1
In the following drawing, the green spheres represent atoms of a certain element. The blue spheres represent atoms of another element. If the spheres of different elements touch, they are part of a single unit of a compound. The following chemical change represented by these spheres may violate one of the ideas of Dalton’s atomic theory. Which one?
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Exercises 3
Identify the postulate of Dalton’s theory that is violated by the following observations: 59.95% of one sample of titanium dioxide is titanium; 60.10% of a different sample of titanium dioxide is titanium.
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Key terms · 4

Dalton’s atomic theory: set of postulates that established the fundamental properties of atoms
law of constant composition: (also, law of definite proportions) all samples of a pure compound contain the same elements in the same proportions by mass
law of definite proportions: (also, law of constant composition) all samples of a pure compound contain the same elements in the same proportions by mass
law of multiple proportions: when two elements react to form more than one compound, a fixed mass of one element will react with masses of the other element in a ratio of small whole numbers

Learn 2.1 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 2.1 in the textbook · This section on openstax.org

Early Ideas in Atomic Theory: practice problems

2 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 1

In the following drawing, the green spheres represent atoms of a certain element. The blue spheres represent atoms of another element. If the spheres of different elements touch, they are part of a single unit of a compound. The following chemical change represented by these spheres may violate one of the ideas of Dalton’s atomic theory. Which one?

This equation contains the starting materials of a single, green sphere plus two smaller, blue spheres bonded together. When the starting materials are added together the products of the change are one blue sphere bonded with one green sphere plus one blue sphere bonded with one green sphere.

Exercises 3

Identify the postulate of Dalton’s theory that is violated by the following observations: 59.95% of one sample of titanium dioxide is titanium; 60.10% of a different sample of titanium dioxide is titanium.

Key terms · 4

Dalton’s atomic theory: set of postulates that established the fundamental properties of atoms
law of constant composition: (also, law of definite proportions) all samples of a pure compound contain the same elements in the same proportions by mass
law of definite proportions: (also, law of constant composition) all samples of a pure compound contain the same elements in the same proportions by mass
law of multiple proportions: when two elements react to form more than one compound, a fixed mass of one element will react with masses of the other element in a ratio of small whole numbers

Learn 2.1 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 2.1 in the textbook · This section on openstax.org