This lesson traces early explanations of matter from ancient Greek philosophy to John Dalton’s atomic theory. It explains how Dalton’s ideas describe the composition of substances and what happens to atoms during chemical changes.
In the fifth century BC, Greek philosophers Leucippus and Democritus proposed that matter consists of tiny, finite particles they called atomos, from a Greek word meaning “indivisible.” They imagined atoms as moving particles that differed in shape and size and could join together.
All flashcards
Law of definite proportions
Samples of the same pure compound have the same elements in the same proportions by mass.
Law of multiple proportions
When two elements form multiple compounds, their masses compare in small whole-number ratios when one mass is fixed.
Dalton’s conservation postulate
Atoms are neither created nor destroyed during a chemical change; they are rearranged.
Dalton’s view of compounds
Compounds contain atoms of two or more elements in fixed, small whole-number ratios.
Aristotle’s view of matter
Matter consists of combinations of fire, earth, air, and water and can be divided indefinitely.
Quiz questions
Which account of matter was associated with Aristotle?Answer: Matter consists of four elements and can be divided indefinitely.
According to Dalton, how do atoms of different elements compare?Answer: They have different properties and are not the same type of atom.
In Dalton’s theory, what distinguishes an element from a compound?Answer: An element has one type of atom; a compound has atoms of multiple elements.
A reaction diagram has four atoms of one element before a reaction and three afterward. Which Dalton postulate does this contradict?Answer: Atoms are not created or destroyed during chemical changes.
Two samples known to be the same pure compound have different total masses. What should be true of their elemental mass proportions?Answer: Their elemental mass proportions should be the same.
Based on Chemistry 2e by Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson, PhD (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.