Discovery of the Atom, OpenStax Flashcards
What is the importance of Leucippus and Democritus in the history of atoms?
These two Greeks considered the question of whether a substance can be divided without limit into ever smaller pieces in the fifth century BCE.
Democritus believed that there is a smallest unit that cannot be further subdivided, called…
The atom.
The Greeks believed that atoms were in constant motion, which is…
Correct!
Atoms themselves can be subdivided, but…
Their identity is destroyed in the process.
The masses of reactants in specific chemical reactions always…
Have a particular mass ratio. Very strong indirect evidence that there are basic units (atoms and molecules) that have these same mass ratios.
Amedeo Avogadro…
Developed the idea of a fixed number of atoms and molecules in a mole, known as Avogadro’s number.
Johann Josef Loschmidt was the first to…
Measure the value of the constant in 1865 using the kinetic theory of gases.
Dmitri Mendeleev…
Developed the periodic table of elements in the mid-19th-century.
In addition to developing the period table of elements, Mendeleev…
Left spots in the periodic table, predicting the existence of then-unknown elements to complete it. These elements were discovered and were determined to have properties predicted by Mendeleev, which led to his periodic table to be universally accepted.
What is the kinetic theory of gases?
Kinetic theory is based on the existence of atoms and molecules in random thermal motion and provides a microscopic explanation of the gas laws, heat transfer, and thermodynamics.
Because it works so well, kinetic theory…
Is another strong indication of the existence of atoms. But still indirect evidence.
The first truly direct evidence of atoms is credited to…
Robert Brown, a Scottish botanist.
What is Brownian motion?
The random thermal motions of fluid molecules colliding with particles in the fluid. Pollen grains on still water.
What can Brownian motion teach us?
By examining Brownian motion, the size of the molecules can be calculated. The smaller and more numerous they are, the smaller the fluctuations in the numbers striking different sides.
Who explained precisely how Brownian motion could be used to measure the size of atoms and molecules?
Albert Einstein.
