2.1 Early Ideas in Atomic Theory Flashcards
Dalton’s atomic theory
Set of postulates that establish the fundamental properties of atoms.
Dalton’s atomic theory postulates 1
- Matter is composed of exceedingly small particles called atoms. An atom is the smallest unit of an element that can participate in a chemical change.
In the following drawing, the green spheres represent atoms of a certain element. The purple spheres represents atoms of another element. If the spheres touch, they are part of a single unit of a compound. Does the following chemical change represented by these symbols violate any of the ideas of Dalton’s atomic theory? If so, which one?
The starting materials consist of two green spheres and two purple spheres. The products consist of only one green sphere and one purple sphere. This violates Dalton’s postulate that atoms are neither created nor destroyed during a chemical change, but are merely redistributed. (In this case, atoms appear to have been destroyed.)
In the following drawing, the green spheres represent atoms of another element. If the spheres touch, they are part of a single unit of a compound. Does the following chemical change represented by these symbols violate any of the ideas of Dalton’s atomic theory? If so, which one?
The starting materials consist of four green spheres and two purple spheres. The product consists of four green spheres and two purple spheres. This does not violate any of Dalton’s postualtes: Atoms are neither created nor destroyed, but are redistributed in small whole-number ratios.
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.
A sample of compound A (a clear, colorless gas) is analyzed and found to contain 4.27 g carbon and 5.69 g oxygen. A sample of compound B (also a clear, colorless gas) is analyzed and found to contain 5.19 g carbon and 13.84 g oxygen. Are these data an example of the law of definite proportions, the law of multiple proportions, or neither? What do these data tell you about substances A and B?
In compound A, the mass ratio of oxygen to carbon is:
1.33 g O / 1 g C
In compound B, the mass ration of oxygen to carbon is:
2.67 g O / 1 g C
The ratio of these is 1.33 g O / 1 g C / 2.67 g O / 1 g C = 1/2
This supports the law of multiple proportions. This means that A and B are different compounds, with A having one-half as much oxygen per amount of carbon (or twice as much carbon per amount of oxygen) as B. A possible pair of compounds that would fit this relationship would be A = CO and B = CO2.
A sample of compound X (a clear, colorless, combustible liquid with a noticable odor) is analyzed and found to contain 14.13 g carbon and 2.96 hydrogen. A sample of compound Y (a clear, colorless, combustible liquid with a noticeable odor that is slightly different from X’s odor) is analyzed and found to contain 19.91 g carbon and 3.34 g hydrogen. Are these data an example of the law of definite proportions, the law of multiple proportions, or neither? What do these data tell you about substances X and Y?
In compound X, the mass ratio of carbon to hydrogen is 14.13 g C / 2.96 g H. In compouhnd Y, the mass ratio of carbon to hydrogen is 19.91 g C / 3.34 g H. The ratio of these ratios is 14.13 g C / 2.96 g H / 19.91 g C / 3.34 g H = 4.77 g C/ g H / 5.96 g C / g H = 0.800 = 4/5. This small, whole-number ratio supports the law of multiple proportions. This means that X and Y are different compounds.
In the following drawing, the green spheres represent atoms of a certain element. The purple 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?
The starting materials consist of one green sphere and two purple spheres. The product consist of two green spheres and two purple spheres. This violates Dalton’s postulate that atoms are not created during a chemical change, but are merely redistributed.
Dalton’s atomic theory postulates 2
- An element consists of only one type of atom, which has a mass that is characteristic of the element and is the same for all atoms of that element A macroscopic sample of an element contains an incredibly large number of atoms, all of which have identical chemical properties.
Dalton’s atomic theory postulate 3
- Atoms of one element differ in properties from atoms of all other elements.
Dalton’s atomic theory postulate 4
- A compound consists of atoms of two or more elements combined in a small, whole-number ratio. In a given compound, the numbers of atoms of each of its elements are always present in the same ratio.
Dalton’s atomic theory postulate 5
- Atoms are neither created nor destroyed during a chemical change, but are instead rearranged to yield substances that are different from those present before the change
Which postulate of Dalton’s theory is consistent with the following 6 concerning the weights of reactants and products? When 1000 grams of solid calcium carbonate is heated, 44 grams of carbon dioxide and 56 grams of calcium oxide are produced.
Dalton’s fourth postulate, which states that a chemical reaction is a rearrangemet of atoms. This is also known as the law of conservation of mass.
Identify the postulate of Dalton’s theory that is violated by the following observations: 59.95% of one sample oof titanium dioxide is titanium; 60.10% of a different sample of titanium dioxide is titanium.
This statement violates Dalton’s fourth postulate: In a given compound, the numbers of atms of each type (and thus also the percentage) always have the same ratio.
