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.
Go to this website
he made up the periodic tables
Dmitri Mendeleev.
The columns are known as groups.
no, they depend on what country your in
15 (the 15th column from the left) or also called 5A on some periodic tables.
Periodic tables are important in most scientific classes because they help understand similarity of properties and reactions of elements.
7The Periodic Table has 7 periods and 18 groups.