Development of the periodic table

Mar 13
In this free science revision tuition programme sample, we look at the Development of the Periodic Table.

The Development of the Periodic Table: We know that the elements are arranged in the periodic table, but we need to know a bit about the history of how this was developed. In the early 1800s, elements were arranged by atomic weight and their physical properties.

Limitations of Early Periodic Tables
At this time, scientists had no clue about subatomic particles or atomic numbers. The only thing they were able to measure was atomic weight. They did see periodic patterns in the atomic weights, which is why it is called a periodic table.

Due to them only having the atomic weights, some elements were placed in the wrong groups as it only used atomic weight, not the properties.

Mendeleev's Periodic Table
In 1869 Dmitri Mendeleev took 50 known elements and started to arrange them, leaving gaps where he thought elements should be that still need to be discovered. He arranged them into vertical columns based on their properties and horizontally by increasing atomic weight. He noticed a pattern and left gaps where elements they knew about did not fit the pattern.

Advancements in the Development of the Periodic Table
Mendeleev was good at predicting the missing elements' chemical and physical properties. For example, the element he called eka-silicon is what we know today as germanium.

Mendeleev's Contributions to Modern Periodic Table Development
Mendeleev didn't put them in the strict order of atomic weight, but he also used the properties. As we understood the structure of atoms more and more, this proved to be the right thing to do. This is because isotopes had not been discovered yet and wouldn't be until the early 20th century.

Modern Periodic Table and Atomic Number
The modern-day periodic table is organised by proton or atomic number. Remember that the number of protons is unique to each element. If the number of protons changes, the element changes.

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