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The Periodic table (Mendeleev (Published first periodic table in 1869,…
The Periodic table
Mendeleev
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When he did this he noted that the chemical properties of the elements and their compounds showed a periodic trend.
He then arranged the elements by putting those with similar properties below each other into groups.
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Mendeleev left gaps in his table to place elements not known at the time. By looking at the chemical properties and physical properties of the elements next to a gap, he could also predict the properties of these undiscovered elements.
Modern periodic table
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After the discovery of protons, scientists realised that the atomic number of an element is the same as the number of protons in its nucleus.
In the modern periodic table, the elements are arranged according to their atomic number - not their relative atomic mass.
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rows, called periods, in order of increasing atomic number
vertical columns, called groups, where the elements have similar properties
Electronic Configuration
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Different shells can hold different maximum numbers of electrons. Electrons occupy shells starting with the innermost one. They begin to occupy the next shell when a shell becomes full.
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The electronic configuration of an atom can be predicted from its atomic number. For example, the atomic number of sodium is 11. Sodium atoms have 11 protons and so 11 electrons:
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