3. The periodic table allowed scientists to predict the properties and sort the elements with those that had the similar properties, allowing us to have comparisons
4. John Newlands periodic table was organised by the weights of the elements that had been discovered. However this was incomplete as many elements were not found yet and were placed in the wrong group.
Dmitri Mendeleev realised that there were undiscovered elements and added gaps to John Newlands table for those unknown elements. Furthermore Mendeleev sorted the periodic table by atomic mass. This meant that he was able to accurately predict the properties.