Describe the development of the modern periodic table.

Lavoisier, Newlands, Mendeleev, and Moseley are contributors of today’s modern periodic table. Brief explanations on each of the scientists’ contributions are provided below:

1. Lavoisier wrote the fist list of elements. His list consisted of 33 elements. He made two broad categories – metals and nonmetals. Some of Lavoisier’s elements were later found to be mixtures or compounds.


2. In 1864, John Newlands took the 60 known elements of his time and arranged them by atomic weights...

Lavoisier, Newlands, Mendeleev, and Moseley are contributors of today’s modern periodic table. Brief explanations on each of the scientists’ contributions are provided below:

1. Lavoisier wrote the fist list of elements. His list consisted of 33 elements. He made two broad categories – metals and nonmetals. Some of Lavoisier’s elements were later found to be mixtures or compounds.


2. In 1864, John Newlands took the 60 known elements of his time and arranged them by atomic weights and similarities. Thus, he was a forerunner of the concept of periods. Newlands created the ‘Law of Octaves’.
   


3. Mendeleev also based his periodic table on atomic weights. He placed elements that had similar properties underneath each other on his periodic table. He was the first to leave room for elements that were not yet discovered. In 1869, Mendeleev created the periodic law. Mendeleev’s periodic law stated that elemental properties vary with their atomic weights.


4. In 1913, Moseley identified the atomic number of each known element. He modified Mendeleev’s periodic law to state that elemental properties vary with atomic number.

Today’s periodic table is ordered by atomic number. Periods are horizontal rows. Main-sequence elements within the same period have the same number of electron shells. The columns of the modern periodic table are called groups or families. The main-sequence of elements within a periodic group have the same number of valance electrons. The number of an element’s valance electrons determines that element’s reactivity. Therefore, elements within the same periodic group have similar properties. Periodic trends result from today’s arrangement of the elements within the modern periodic table.