BackCH 2: a: Foundational ideas and the development of atomic theory
Terms in this set (13)
What is meant by an atom ?
An atom is the smallest identifiable unit of an element.
Why was Brownian motion historically important to chemistry?
It provided persuasive evidence that matter is particulate rather than continuous, because the random motion of visible particles was explained by collisions with unseen molecules.
What did Einstein contribute to the interpretation of Brownian motion?
He provided a quantitative explanation showing that the motion results from molecular bombardment caused by the thermal motion of surrounding molecules.
What was Jean Perrin’s significance in the history of atomic theory?
He experimentally confirmed Einstein’s explanation of Brownian motion, thereby strengthening the case for the real existence of atoms and molecules.
Why did the atomic view of matter not dominate ancient thought, despite being proposed by Greek philosophers?
There was no experimental means of testing competing explanations, and more influential philosophical views, especially those associated with Aristotle, prevailed.
State the law of conservation of mass.
In a chemical reaction, matter is neither created nor destroyed.
How does the law of conservation of mass support atomic theory?
It suggests that matter consists of particles that are rearranged during chemical change rather than created or destroyed.
State the law of definite proportions.
All samples of a given compound have the same proportions of their constituent elements, regardless of source or method of preparation.
Why does the law of definite proportions support the idea of atoms?
If compounds are made from atoms combining in fixed ratios, then the mass ratios of the elements in those compounds must also remain fixed.
State the law of multiple proportions.
When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are related by small whole-number ratios.
How is the law of multiple proportions different from the law of definite proportions?
The law of definite proportions concerns multiple samples of the same compound, whereas the law of multiple proportions compares different compounds made from the same two elements.
State the four central propositions of Dalton’s atomic theory.
Each element is composed of tiny, indestructible atoms.
All atoms of a given element share the same mass and properties.
Atoms combine in simple whole-number ratios to form compounds.
Chemical reactions involve rearrangement of atoms, not conversion of one element into another.
Which part of Dalton’s atomic theory is now known to be incomplete?
The claim that all atoms of a given element have the same mass is incomplete because isotopes of the same element can have different numbers of neutrons and therefore different masses.