In 1869, Dmitri Mendeleev improved on Newlands' idea. Like Newlands, he too organised the elements known at the time in order of relative atomic mass. He also realised that the physical and chemical properties of every eighth element were similar, so he arranged them so that elements with similar properties were placed in the same column. This method is the same as Newlands.
However, Mendeleev noticed that by organising the elements this way, there would be gaps in the rows (now known as periods) as there wasn't an element that hadn't been discovered that had the required atomic mass. To overcome this problem, he left gaps in the table where he believed that a particular undiscovered element should be placed. From this, he could predict the mass of the missing elements and he could also predict their properties.
One problem with Mendeleev's periodic table was that he arranged the elements in order of atomic mass. This meant that some of the elements weren't in placed in the same group as other elements with the same properties. However, he overcame this problem by placing them in the correct rows, even though this meant that the pattern of ascending atomic mass was broken.
Due to the fact that Mendeleev correctly predicted the properties of undiscovered elements, other chemists were convinced by his ideas and therefore decided to use his table. This is why Mendeleev is was credited for the invention of the Periodic Table.
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