Atomic Structure and Chemical Laws

Vocabulary flashcards covering early chemical laws, Dalton's atomic theory postulates, and key atomic structure experiments from lecture notes.

Law of Definite Proportions

A principle stating that a given chemical compound always contains the same elements in the same proportions by mass.

Dalton’s Atomic Theory - Postulate 1

States that elements are composed of indestructible particles called atoms; this postulate is false because atoms are NOT indestructible.

Dalton’s Atomic Theory - Postulate 2

States that all atoms of a given element are identical and that atoms of one element are different from all other elements; this postulate is false because they are not identical.

Dalton’s Atomic Theory - Postulate 3

States that compounds are composed of atoms of more than one element; this postulate is true.

Dalton’s Atomic Theory - Postulate 4

States that a chemical reaction involves only the separation, combination, or rearrangement of atoms, and does not result in their creation or destruction; this postulate is true.

Law of Conservation of Mass

A principle stating that mass is neither created or destroyed during a chemical reaction ($\text{mass of reactants} = \text{mass of products}$).

Cathode Ray Tube (J.J. Thomson)

An experiment where a beam made of electrons traveled from the negative electrode and was deflected by electromagnetic fields, behaving the same way regardless of metal and allowing determination of the charge-to-mass ratio.

Milikan’s Oil Drop Experiment

An experiment in which tiny oil droplets were sprayed between charged metal plates and adjusted until suspended by balancing gravitational & electrical force; calculated droplet charges to prove electrical charge is quantized and determine the electron's charge.

Rutherford’s Gold Foil Experiment

An experiment where alpha particles were fired at thin gold foil; most passed straight through, some were slightly deflected, and a few bounced straight back, demonstrating that the atom has a tiny, dense, positively charged center called the nucleus.

Mass deficit

The condition where atomic masses were greater than the number of protons alone could account for, leading scientists to propose the existence of the neutron.

James Chadwick

The scientist who confirmed the neutron, which explained the “missing mass” in atomic nuclei.