ATOMIC STRUCTURE

3.2 - Isotopes

Let's take a look at the carbon atom in detail. There are two types of carbon atoms that are found in nature. We call them carbon-12 and carbon-13. Using symbols, carbon-12 and carbon-13 can be written as follows:

carbon-12	carbon-13
The symbol describes carbon-12 as follows: "C" indicates the atom is Carbon Z = 6 indicates carbon-12 has 6 protons A = 12 indicates that the mass number is 12 number of neutron = 12 - 6 = 6 neutrons	The symbol describes carbon-13 as follows: "C" indicates the atom is Carbon Z = 6 indicates carbon-13 has 6 protons A = 13 indicates that the mass number is 13 number of neutron = 13 - 6 = 7 neutrons

Points to note:

• carbon-12 and carbon-13 are atoms that have the same atomic number but different mass numbers. Carbon-12 and carbon-13 are called isotopes.
• carbon-12 has 6 neutrons and carbon-13 has 7 neutrons.
• Isotopes of the same element (i.e. such as carbon-12 and carbon-13) have similar chemical properties.

Section 4.5
Isotopes ..p85

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