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Classification of Elements The Periodic Table Arranging The Elements The Russian chemist Dmitri Mendeleev uncovered evidence that consisted of a huge collection of facts about the 63 elements that had been discovered by the mid-1800s His clues had to do with the physical and chemical properties of these elements Mendeleev was convinced that he could arrange the elements so that those with similar properties were grouped together Mendeleev made a card for each element including the atomic mass density color and melting point He also included the elements valence bonding power Mendeleev looking for patterns arranged the card so that the atomic mass increases If he started with lithium the next would be beryllium Then would come boron carbon nitrogen oxygen and flourine With the cards arranged in this order Mendeleev noticed that the pattern of valences was 1 2 3 4 3 2 1 Seven elements in a row and a pattern of valences repeating themselves As he arranged all 63 cards in this manner in doing so he also saw something even more remarkable When the elements were arranged in this way they fell into columns one under the other All the elements in one column had the same valence and showed similar physical and chemical properties Mendeleev designed a periodic table in wich the elements were arranged in order of increasing atomic mass The periodic law states that the physicaland chemical properties of the elements are periodic functions of their atomic numbers The periodic table of the elements is one of the most important tools of a scientist especially a chemist The periodic table is a classification system a way of organizing vast amounts of information in a logical usable meaningful way The columns the elements are placed in are called groups or families Elements within the group have similar but not identical properties For example lithium Li sodium Na potassium
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