Unit 1: 2.3: The History of the Atom

Question 1

The theory that matter is made up of small particles (atoms) that have properties characteristic of an element

Answer 1

Dalton’s atomic theory

Question 2

A beam of electrons.

Answer 2

cathode ray

Question 3

A negatively charged subatomic particle found outside the nucleus; a fundamental particle of nature.

Answer 3

electron

Question 4

The emission of particles during nuclear decay.

Answer 4

radioactivity

Question 4

A stable subatomic particle occurring in all atomic nuclei, with a positive electric charge equal in magnitude to that of an electron, but of opposite sign.

Answer 4

protons

Question 4

The center (core) of an atom, consisting of the protons and neutrons. It accounts for almost all of the mass, but almost none of the volume, of an atom.

Answer 4

nucleus

Question 4

A subatomic particle found in the nucleus that has no charge and a mass slightly greater than 1 u.

Answer 4

neutron

Question 5

Dalton concluded that matter was made up of atoms. What additional insight about atoms did Thomson’s experiments reveal?

Answer 5

Thomson’s experiments showed that cathode rays have a negative charge and that the atom was composed of small particles. This led Thomson to propose the plum-pudding model of the atom.

Question 6

How did our model of the atom change after Rutherford’s experiment?

Answer 6

Rutherford showed that the positive charge of the atom was not dispersed throughout the atom but was instead concentrated in a small are (the nucleus). This led Rutherford to propose the nuclear model of the atom.