Answer: B - All matter is composed of tiny, discrete particles called atoms.
John Dalton was an English chemist, physicist, and meteorologist. He is best known for introducing the atomic theory into chemistry and his research into color blindness, sometimes referred to as Daltonism.
Dalton's Theory's 5 Key Points
- Everything is composed of atoms, indivisible building blocks of matter. Atoms cannot be created, subdivided, or destroyed.
- All atoms of a specific element are identical.
- Atoms of different elements vary in size and mass.
- Compounds are produced through different whole-number combinations of atoms (Dalton's "compounds" are now referred to "molecules").
- A chemical reaction results in the rearrangement of atoms in the reactant and product compounds.
Since Dalton's conclusions are based on an empirical analysis of experimental results, this is the first officially scientific atomic theory. Dalton's work led him to develop the Law of Conservation of Mass (matter cannot be created nor destroyed) and the Law of Constant Composition (elements combine in a fixed ratio to make up molecules).
Dalton's atomic theory expanded in 1897 when English physicist J.J. Thomson began experimenting with a cathode ray tube. Using the cathode ray tube, Thomson discovered electrons, which are tiny particles with a negative electric charge.
The atomic theory was further expanded in 1911 when Thomson's colleague Ernest Rutherford began experimenting with alpha particles to probe the atomic structure of gold foil. In his now-famous Gold Foil Experiment, Rutherford saw that while most alpha particles passed right through the gold foil, a few deflected to the side, and some even bounced back. This experiment provided Rutherford with evidence that the majority of an atom's mass is contained in the center of the atom. Rutherford combined this discovery with Thomson's idea of electrons to develop a better model for particles wherein much smaller negatively charged electrons surround a large, positively charged nucleus, much like planets around a sun.
