The Nuclear Model of the Atom PDF

Preview

Summary

DLT...

Description

The Atomic Structure and the Chemical Elements, Physical Science The Nuclear Model of the Atom

Objective In this lesson, you should be able to describe the nuclear model of the atom and the location of its major components (protons, neutrons, and electrons). If you have lived during the time when the atom was discovered, how would you describe its structure?

Learn about it! As subatomic particles were discovered, models for their arrangement in the atom were developed. There was J. J. Thomson’s plum-pudding model, which he proposed after his discovery of the electrons. Then there was Ernest Rutherford’s planetary model, proposed after the discovery of the protons in the nucleus.

The Nuclear Model The nuclear model states that the nucleus is small, dense, and located at the center of the atom. It contains protons and neutrons. Overall, it is positively charged. It contains nearly all the mass of the atom. The electrons orbit around it.

The nuclear model has been deduced from the experiment done by Rutherford.

Geiger-Marsden Experiment Under Rutherford's supervision, Hans Geiger, his assistant, and Ernest Marsden, an undergraduate student, shot a narrow beam of alpha particles at a very thin sheet of gold foil and measured the scattering pattern on a fluorescent screen. It was observed that some particles deflected, and others penetrated through the sheet of gold foil.

There was a force behind the deflections – the repulsion of the positively charged alpha particles by a positively charged material. If this charge existed in a sphere with the same size of the atom, the force should have been weak. This led to the assumption that the charge was concentrated in a small space or sphere. Rutherford proposed that the positive charge, and the mass of the atom were concentrated in a small part of the total volume of the atom called the nucleus.

Issues Involved in the Nuclear Model The main problem in Rutherford's model was how the electrons remained in their orbit without falling into the nucleus. Another problem is the electron's continuous centripetal acceleration and the energy lost through electromagnetic radiation. This energy would make it approach the nucleus while increasing the electrostatic force. The increase in force would increase the acceleration and the emission of energy. Thus, the nucleus and the electrons would collide with each other. This means that the atom would be unstable.

Explore! Imagine you're holding two magnets with the same magnetic poles (north to north poles or south to south poles). When you try to put the magnets together, there is a force acting upon them which makes it difficult to do so. The repulsion between the magnets represents the forces between the alpha particles and the positively charged material in the atom of the gold foil as presented in the Geiger-Marsden experiment of Rutherford and his colleagues. What is the importance of this scenario in studying the structure of the atom?

Try it! Research on the succeeding studies about the nucleus and its characteristics.

What do you think? Rutherford postulated a neutral particle inside the nucleus. How did he come into this conclusion?...