Because the elements that have similar properties are arranged in groups - or 'periods'.
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.
Hydrogen.
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15 (the 15th column from the left) or also called 5A on some periodic tables.
he made up the periodic tables
Dmitri Mendeleev.
no, they depend on what country your in
The columns are known as groups.
Periodic tables are important in most scientific classes because they help understand similarity of properties and reactions of elements.
There are 18 families. They are made according to the properties of elements. So the elements in a group has similar properties.