Elements are arranged in the periodic table in order of increasing atomic number. For example hydrogen has the atomic number of one, helium two, lithium three etc. The first energy level (the one ...

Each element has its own atomic number. Since atoms are neutral, we know then that sodium atoms must also have 11 negative electrons to cancel the charge from 11 positive protons. The first energy ...

The modern periodic table, arranged in rows and columns, was first introduced by Dmitri Mendeleev in 1869. At the time, it included the known elements and their properties, but Mendeleev predicted ...

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