Chapter 4 Physical Science Short Test

The nucleus of an atom contains almost all of its mass. Protons and neutrons, which are both located in the nucleus, have significantly more mass than electrons. While electrons are negatively charged particles that orbit around the nucleus in an electron cloud, they have a negligible mass compared to protons and neutrons. Therefore, the correct answer is nucleus.

Democritus was one of the first people to propose the concept that matter is composed of indivisible particles called atoms. He believed that atoms were eternal, unchangeable, and infinite in number. Democritus' atomic theory was based on the idea that atoms differ in size, shape, and arrangement, which determines the properties of different substances. Although his atomic theory was not widely accepted during his time, it laid the foundation for the development of modern atomic theory.

The electron is the least massive particle among the options given. It has a much smaller mass compared to the proton and neutron, which are both found in the nucleus of an atom. The electron is a subatomic particle that orbits the nucleus and carries a negative charge. Its mass is approximately 1/1836th of the mass of a proton or neutron.

Dalton's model of an atom is best described as a solid sphere because it proposed that atoms were indivisible and indestructible particles with no internal structure. This model suggested that atoms were uniform, dense, and had no empty spaces within them. However, this model was later replaced by more accurate models that described the internal structure of atoms, such as the electron cloud model.

The atomic number of an element refers to the number of protons in the nucleus of an atom. Since all atoms of an element have the same number of protons, the correct answer is atomic #. The mass number refers to the total number of protons and neutrons in the nucleus, which can vary among different isotopes of the same element. The number of isotopes and the number of neutrons can also vary among different atoms of the same element.

Thomson provided the first evidence that atoms contain subatomic particles. He conducted the cathode ray tube experiment and discovered that the rays were composed of negatively charged particles, which he called electrons. This experiment proved the existence of subatomic particles within atoms and laid the foundation for the development of the atomic model. Dalton proposed the atomic theory, Rutherford conducted the gold foil experiment and proposed the nuclear model of the atom, and Bohr proposed the planetary model of the atom. However, Thomson's experiment was the first to provide evidence of subatomic particles within atoms.