atomic nucleus

at the heart of it all

The nucleus (plural, nuclei) is a positively charged region at the center of the atom. It consists of two types of subatomic particles packed tightly together. The particles are protons, which have a positive electric charge, and neutrons, which are neutral in electric charge. Outside of the nucleus, an atom is mostly empty space, with orbiting negative particles called electrons whizzing through it. The Figure 1.1 shows these parts of the atom.

size and mass of the nucleus

The nucleus of the atom is extremely small. Its radius is only about 1/100,000 of the total radius of the atom. If an atom were the size of a football stadium, the nucleus would be about the size of a pea! Click image to the left or use the URL below. URL: Electrons have virtually no mass, but protons and neutrons have a lot of mass for their size. As a result, the nucleus has virtually all the mass of an atom. Given its great mass and tiny size, the nucleus is very dense. If an object the size of a penny had the same density as the nucleus of an atom, its mass would be greater than 30 million tons! Click image to the left or use the URL below. URL:

holding it all together

Particles with opposite electric charges attract each other. This explains why negative electrons orbit the positive nucleus. Particles with the same electric charge repel each other. This means that the positive protons in the nucleus push apart from one another. So why doesnt the nucleus fly apart? An even stronger forcecalled the strong nuclear forceholds protons and neutrons together in the nucleus. Click image to the left or use the URL below. URL: Q: Can you guess why an atomic bomb releases so much energy when it explodes? A: When an atomic bomb explodes, the nuclei of atoms undergo a process called fission, in which they split apart. This releases the huge amount of energy that was holding together subatomic particles in the nucleus.

instructional diagrams

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questions

the nucleus contains

``````a) protons.

b) neutrons.

c) electrons.

-->  d) two of the above
``````

outside of the nucleus, an atom is mostly empty space.

``````-->  a. true

b. false
``````

the nucleus makes up about 1/100th of the total radius of an atom.

``````a. true

-->  b. false
``````

the nucleus has almost all of the mass of an atom.

``````-->  a. true

b. false
``````

what force holds together the nucleus?

``````a) the force of attraction between positive and negative particles.

b) the force of attraction between the nucleus and electrons.

-->  c) the strong nuclear force between protons and neutrons.

d) the weak atomic force between neutrons and electrons.
``````

there is an electric force of repulsion between neutrons and protons.

``````a. true

-->  b. false
``````

diagram questions

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