Because the elements that have similar properties are arranged in groups - or 'periods'.
The chemical properties of the chemical elements are periodically repeated in the Periodic Table.
15 (the 15th column from the left) or also called 5A on some periodic tables.
These chemical elements are called transition metals.
the horizontal rows (not groups) are known as periods.
The elements arranged according to their atomic number in the table are called periodic table.
The periodic tables.
Hydrogen.
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hassium
The columns are known as groups.
no, they depend on what country your in
he made up the periodic tables
Dmitri Mendeleev.