Question

Indicate whether each of the following statements is true or false. If false, correct the statement so that it becomes true. a. Rutherford's bombardment experiments with metal foil suggested that the alpha particles were being deflected by coming near a large, negatively charged atomic nucleus. b. The proton and the electron have similar masses but opposite electrical charges. c. Most atoms also contain neutrons, which are slightly heavier than protons but carry no charge.

Short answer

a. False - Rutherford's bombardment experiments with metal foil suggested that the alpha particles were being deflected by coming near a large, positively charged atomic nucleus. b. False - The proton and the electron have opposite electrical charges, but protons are much heavier than electrons. c. True - Most atoms do contain neutrons, and they indeed have a slightly heavier mass than protons, but carry no electrical charge.

Step-by-step solution

Statement a

Rutherford's bombardment experiments with metal foil suggested that the alpha particles were being deflected by coming near a large, negatively charged atomic nucleus. This statement is false. Rutherford's experiment revealed that alpha particles were deflected by coming near a large, positively (not negatively) charged atomic nucleus. Corrected statement: Rutherford's bombardment experiments with metal foil suggested that the alpha particles were being deflected by coming near a large, positively charged atomic nucleus.

Statement b

The proton and the electron have similar masses but opposite electrical charges. This statement is false. Although protons and electrons have opposite electrical charges, their masses are not similar. Protons are much heavier than electrons (approx. 1836 times heavier). Corrected statement: The proton and the electron have opposite electrical charges, but protons are much heavier than electrons.

Statement c

Most atoms also contain neutrons, which are slightly heavier than protons but carry no charge. This statement is true. Most atoms do contain neutrons, and they indeed have a slightly heavier mass than protons, but carry no electrical charge.

Key concepts

Rutherford's Experiment

Rutherford's experiment was a groundbreaking study in the early 1900s that fundamentally changed our understanding of atomic structure. Conducted by Ernest Rutherford, the experiment involved bombarding thin metal foils, such as gold, with alpha particles. These alpha particles are basically helium nuclei—consisting of two protons and two neutrons, and carry a positive charge—coming from a radioactive source.

A surprising observation was noted. While most alpha particles passed straight through the foil, some were deflected at large angles, and a very small fraction bounced back. This unexpected result led to the revolutionary conclusion that most of an atom's mass and positive charge is concentrated in a tiny central region, which Rutherford termed the "nucleus." This contradicted the then-popular plum pudding model, which assumed that charges were evenly distributed throughout the atom.

To summarize, Rutherford's experiment demonstrated the presence of a dense, positively charged nucleus in the atom. This nucleus was responsible for the deflection of alpha particles, much like how a dense solid object deflects a pathway if something strikes it.

Protons

Protons are one of the fundamental particles that reside in the nucleus of an atom. They carry a positive electrical charge, which is exactly equal in magnitude but opposite to the charge of an electron, which is negative. However, a significant difference between protons and electrons is their mass.

A proton is about 1836 times heavier than an electron. Despite this, the size of a proton is extremely tiny, approximately 1 femtometer ( 1 × 10^{-15} meters). The number of protons in an atom's nucleus defines the chemical element. For example, all hydrogen atoms have one proton, while all oxygen atoms have eight.

Protons, along with neutrons, are known as nucleons. Together, they constitute almost the entire mass of the atom since electrons contribute insignificantly to the total mass.

Neutrons

Neutrons are neutral particles found in the atom's nucleus alongside protons. As the neutral counterpart, neutrons carry no electrical charge, yet they play a crucial role in the atomic structure by stabilizing the nucleus.

Although similar in size to protons, neutrons are slightly heavier. However, this mass difference is so slight it is often negligible in most basic calculations. In the context of atomic mass, neutrons and protons are generally each assigned an approximate mass of 1 atomic mass unit (amu).

Apart from providing atomic stability, neutrons affect the isotope classification of an element. Isotopes are variations of elements where the number of protons remains the same but the number of neutrons varies. An example includes carbon-12, carbon-13, and carbon-14 isotopes, which all have six protons but different numbers of neutrons.

Alpha Particles

Alpha particles are a type of radiation emitted from the decay of certain radioactive materials. Essentially, an alpha particle is composed of two protons and two neutrons, resulting in a +2 charge due to its lack of electrons.

In Rutherford’s experiment, these positive particles were directed at a thin sheet of metal foil, providing key insights into atomic structure. Despite their relatively large mass and double positive charge, most passed through the foil due to the sparse distribution of mass within an atom. However, when these particles occasionally came into close proximity to a dense atomic nucleus, their paths were deflected, leading to the insights we discussed earlier.

Alpha particles have limited penetrating power due to their size and charge. They can be stopped easily by materials such as paper or human skin, making them less dangerous compared to other types of radiation when handled with proper precautions.