The Periodic Table
The Periodic Table
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In 1969, DMITRI MENDELEEV, improved upon earlier tables by arranging 50 known elements by ATOMIC WEIGHT but also considered their PROPERTIES to maintain consistency within groups.
He did NOT force elements into groups that didn’t fit the patterns. Instead he made TWO CHANGES:
1. He left GAPS for elements that he thought would fit the groups but had NOT been DISCOVERED yet.
E.g. Mendeleev PREDICTED the existence and PROPERTIES of EKA-ALUMINIUM (now known as GALLIUM)
2. He CHANGED the ORDERS of some elements, even though their atomic weights did not fit this order.
E.g. Tellurium (Te) and Iodine (I). Usually, elements are lined up by their weight, and Iodine should be before Tellurium because it's lighter. But Mendeleev switched them. He put Tellurium before Iodine because its properties were more similar to the other elements in its column.
These TWO CHANGES turned out to be the right thing to do because:
1. The elements he left gaps for were discovered later and FITTED the pattern he had PREDICTED, which solidified his theories.
2. The discovery of ISOTOPES in the early 20th century confirmed Mendeleev's decision not to place elements in a strict order of atomic weight but to account for their chemical properties. This is because isotopes have different masses BUT they have the SAME CHEMICAL PROPERTIES so they occupy the SAME POSITION on the periodic table.
Eventually Mendeleev’s periodic table developed into the modern table we use today.
The PERIODIC TABLE arranges about 100 ELEMENTS, based on increasing ATOMIC (PROTON) NUMBER.
It reveals repeating patterns in the properties of the elements, which is why properties recur PERIODICALLY.
In 1969, DMITRI MENDELEEV, improved upon earlier tables by arranging 50 known elements by ATOMIC WEIGHT but also considered their PROPERTIES to maintain consistency within groups.
He did NOT force elements into groups that didn’t fit the patterns. Instead he made TWO CHANGES:
1. He left GAPS for elements that he thought would fit the groups but had NOT been DISCOVERED yet.
E.g. Mendeleev PREDICTED the existence and PROPERTIES of EKA-ALUMINIUM (now known as GALLIUM)
2. He CHANGED the ORDERS of some elements, even though their atomic weights did not fit this order.
E.g. Tellurium (Te) and Iodine (I). Usually, elements are lined up by their weight, and Iodine should be before Tellurium because it's lighter. But Mendeleev switched them. He put Tellurium before Iodine because its properties were more similar to the other elements in its column.
These TWO CHANGES turned out to be the right thing to do because:
1. The elements he left gaps for were discovered later and FITTED the pattern he had PREDICTED, which solidified his theories.
2. The discovery of ISOTOPES in the early 20th century confirmed Mendeleev's decision not to place elements in a strict order of atomic weight but to account for their chemical properties. This is because isotopes have different masses BUT they have the SAME CHEMICAL PROPERTIES so they occupy the SAME POSITION on the periodic table.
Eventually Mendeleev’s periodic table developed into the modern table we use today.
The PERIODIC TABLE arranges about 100 ELEMENTS, based on increasing ATOMIC (PROTON) NUMBER.
It reveals repeating patterns in the properties of the elements, which is why properties recur PERIODICALLY.
