 Isotopes and Atomic Symbols

Atomic Symbols: The atom of each element is made up of electrons, protons and neutrons. All atoms of the same neutral element have the same number of protons and electrons but the number of neutrons can differ. Atoms of the same element but different neutrons are called isotopes. Because of these isotopes it becomes necessary to develop a notation to distinguish one isotope from another - the atomic symbol. The atomic symbol has three parts to it:

• 1. The symbol X: the usual element symbol
• 2. The atomic number A: equal to the number of protons (placed as a left subscript)
• 3. The mass number Z: equal to the number of protons and neutrons in the isotope (placed as a left superscript)
• Examples 1:

Consider two isotopes of gallium, one having the 37 neutrons and the other having 39 neutrons. Write the atomic symbols for each isotope. Solution: Example 2:

How many neutrons does the isotope of copper with mass number Z = 65 have? Solution: From the periodic table we see that copper has an atomic number of 29. Since Z is the number of protons plus the number of neutrons, then No. neutrons = 65 - 29 = 36

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C101 Class Notes
Prof. N. De Leon   