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ATOMIC STRUCTURE AND ISOTOPES
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The Structure of the Atom Today |
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Today an atom's structure (above) is similar to Rutherford's model of 1910. |
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At the centre of the atom protons and neutrons form a tiny but 'heavy' nucleus. |
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Protons are positively charged. |
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Neutrons have no charge, i.e. are neutral. |
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Protons and neutrons have the same mass. |
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Electrons are negatively charged and have almost no mass. |
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Electrons occupy a lot of 'empty' space. |
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Electrons orbit the nucleus very quickly |
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A Summary of the Sub-atomic Particle Properties |
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Particle |
Mass |
Charge |
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Proton |
1 |
+1 |
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Neutron |
1 |
0 |
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Electron |
1/2000 |
-1 |
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Some Examples of Atoms (Protons in red / Neutrons in blue) |
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Hydrogen |
Helium |
Lithium |
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An atom's ATOMIC NUMBER (Z) = the number of protons in the nucleus. |
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An atom's NEUTRON NUMBER (N) = the number of neutrons in the nucleus. |
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An atom's MASS NUMBER (A) = total number of protons + neutrons in the nucleus. |
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Notation used to represent an atom |
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Atomic and Mass Numbers for Hydrogen, Helium and Lithium |
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Atom |
Protons (Z) |
Neutrons (N) |
Atomic Number (Z) |
Mass Number (A) |
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Hydrogen |
1 |
0 |
1 |
1 |
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Helium |
2 |
2 |
2 |
4 |
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Lithium |
3 |
4 |
3 |
7 |
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The number of electrons in a neutral atom = the number of protons in the nucleus |
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Isotopes |
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Isotopes are atoms with the same number of protons but different numbers of neutrons. |
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The isotopes of an element have the same atomic number but different mass numbers. |
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Many elements have isotopes but for most elements only one or two isotopes are stable. |
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Unstable isotopes are usually radioactive. This means they emit radiation to become stable. |
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An Example of an Isotope (Protons in red / Neutrons in blue) |
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Hydrogen |
Deuterium (an isotope of Hydrogen) |
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Atomic Number = 1 / Mass Number = 1 |
Atomic Number = 1 / Mass Number = 2 |
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