Understanding the Nucleus of an Atom

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The Composition of the Nucleus

1. Matter is made up of very small particles called atoms.

2. Each atom has a very small and very dense core known as the nucleus.

3. Most of the mass of the atom is contained in the nucleus.

4. The electrons move in orbits around the nucleus.

5. The diameter of the nucleus is about 100 000 times smaller than the diameter of the atom.

6. This means that there are lots of empty spaces within an atom.

7. The subatomic particles in a nucleus are called nucleons.

8. The two types of nucleons are protons and neutrons.

9. The proton is a positively charged particle. It carries a charge of +e, where e is equal to 1.6 × 10-19 C.

10. The neutron carries no charge. The neutrons has approximately the same mass as the proton.

11. The number of protons in the nucleus of an atom is known as the proton number, Z.

12. The total number of protons and neutrons in the nucleus of an atom is known as nucleon number, A or mass number.

13. Then number of neutrons, N = A – Z

Nuclide Notation

1. A nuclide is a type of atom with a particular nucleon number. This term is also used for a type of nucleus.

2. The nuclide notation of an atom gives the symbol of the elements, the proton number and the nucleon number of the atom.

Isotopes

1. Isotopes are atoms of the same elements with the same numbers of protons but different number of neutrons.

2. isotopes have the same proton number but different nucleon numbers.

3. All isotopes of an element have the same chemical properties because their electrons are arranged in exactly the same way.

4. Their physical properties such as densities, boiling points and melting points are different.

5. Some elements in nature such as oxygen,carbon, and bromine consist of a mixture of isotopes.

6. Some isotopes of an element are stable while some are unstable. The unstable isotopes or radioisotopes.

7. Radioisotopes will undergo spontaneous decay to emit radioactive rays such as alpha, beta and gamma rays. After radioactive decay, the proton number and nucleon number of the radioisotope may be changed.