Simple model of the atom - Chemical Ideas 2.1
Structure of an atom
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You can use the nuclear symbol in order to tell you how many protons, neutrons and electrons there are in an atom.
As you can see in the example above a carbon atom has a mass number of 6 and an atomic number of 12 from this I can tell that:
· the mass number is 6 so the number of protons is 6
· the number of protons is 6 so the number of electrons is 6
· the atomic number is 12 and there are 6 protons so the number of neutrons is 6
· the mass number is 6 so the number of protons is 6
· the number of protons is 6 so the number of electrons is 6
· the atomic number is 12 and there are 6 protons so the number of neutrons is 6
Isotopes
An isotope is the same element with a different mass number. This is because these two atoms have a different number of neutrons. For example
1) Chlorine-35 has a mass of 35 and an atomic number 17
Chlorine-35 has 17 protons and 18 neutrons.
2) Chlorine-37 has a mass of 37 and an atomic number 17
Chlorine-37 has 17 protons and 20 neutrons.
Chlorine appears on the periodic table as having a mass of 35.5 this is because this is the weighted average of the two isotopes. If you know the relative atomic masses and the relative abundance of the two isotopes then it is possible to work out the relative atomic mass of the isotopes.
Example
If there is 75% of 35Cl and 25% of 37Cl in a sample of chlorine what is the average relative atomic mass?
(35x75) + (37x25) = 35.5
100
1) Chlorine-35 has a mass of 35 and an atomic number 17
Chlorine-35 has 17 protons and 18 neutrons.
2) Chlorine-37 has a mass of 37 and an atomic number 17
Chlorine-37 has 17 protons and 20 neutrons.
Chlorine appears on the periodic table as having a mass of 35.5 this is because this is the weighted average of the two isotopes. If you know the relative atomic masses and the relative abundance of the two isotopes then it is possible to work out the relative atomic mass of the isotopes.
Example
If there is 75% of 35Cl and 25% of 37Cl in a sample of chlorine what is the average relative atomic mass?
(35x75) + (37x25) = 35.5
100