The origins of the periodic table lie in the work of a British scientist, John Newlands. In 1863, John Newlands divided the known 56 elements of matter into 11 groups. He did this based on their chemical properties and how they reacted. It wasn’t until 1869, that Dimitri Mendeleev took this work and began to order them by their Atomic Number as well, importantly leaving gaps in the periodic table for undiscovered elements. The layout of Mendeleev's periodic table led to the adoption of Groups and Periods to relate the relative position of elements with similar characteristics.
Atomic number is the number of protons in the nucleus
John Newlands was a British scientist who divided 56 elements into groups
Groups are the columns of the periodic table where the elements are arranged vertically due to their similarities of properties.
Periods are the rows of the periodic table. As you go along periods the number of protons and neutrons increases and the number of electron shells remains the same.
Dmitri Mendeleev was a Russian scientist who in 1869 proposed the first structure of the periodic table