Question

Short report on how the modern Periodic was developed.

This must include the following:

What is meant by the term 'chemical element'?

What early work was done by John Newlands and Dmitri Mendeleev to develop the periodic table?

How was Mendeleev able to explain the anomalies in his table and how was he able to make predictions from it that could be tested experimentally.

i need a quick response thank you!!!!

Answer 1

• A chemical element is a substance that cannot be broken down into simpler substances by chemical means.
• John Newlands and Dmitri Mendeleev proposed early versions of the periodic table based on the atomic masses of the elements.
• Mendeleev's table was more accurate than Newlands', and he was able to explain anomalies in his table by predicting the properties of elements that had not yet been discovered.
• The modern periodic table is based on the atomic number of the elements, and it is divided into periods and groups.

The modern periodic table is a powerful tool for understanding the properties of the elements.

Answer 2

Periodic Table :

• It's a table wherein the elements of similar properties are placed together.

Dobereiner’s Law Of Triads :

• Dobereiner first classified the elements in 1800, into the group of three with similar properties in a way that the atomic weight of the middle element was the arithmetic mean of the rest of the two elements . For example : the average of the atomic mass of lithium and potassium [(7+39)/2] = Atomic mass of Sodium = 23 ,but it isn't true for every element and hence got called off by the scientific community.

Newlands's Octaves :

• Later on, In 1865, an English Chemist John Alexander Newland suggested the law of octaves . According to this law, elements can get arranged in an increasing order of their atomic mass wherein every eighth and first element would have similar properties as seen in the node of an octave of music .
• For example : The eighth element from Carbon is Silicon and they both have numerous similarities between them like the same group (14) and have 4 valance electrons each etc. but law got dismissed as it could not be satisfactory for all the elements up above calcium.

Mendeleev's periodic table:

• In 1869, after the failure of Newlands's Octaves, Dmitri Mendeleev, a Russian chemist ,published his periodic table. The table was a collection of known elements at that time placed into an increasing order according to their atomic mass . The vertical rows had elements with similar properties and were called ,'columns'. The horizontal rows were known as ,'periods'.
• According to him,the physical and chemical properties were somehow related to the atomic mass in a periodic way and hence he stated, "The properties are a periodic function of their atomic mass."
• While he were arranging the elements,he left few gaps in the periods simply because he thought the elements which were to be placed there weren't discovered at the time which made the table more significant.
• He later then also worked on the atomic mass of the same missing elements or undiscovered elements which later on found to be proven right as per he predicted. He predicted the properties of elements which were unknown at the time and later on scientists found out the elements which resembled the properties stated by him e.g. The three elements,'eka-boron' ,'eka-silicon',and 'eka-aluminium' which were to be placed after their respective elements were found out to be Scandium, Germanium & Gallium respectively, and showed exact properties as described by him.

The modern Periodic Table :

• The modern Periodic table is the arrangement of elements on the basis of atomic number and not atomic mass as in Mendeleev's periodic table and thereby can be termed as ,"The physical and chemical properties of the elements are periodic functions of their atomic numbers".
• As of now,a total number of 118 elements have been found and classified by the scientists.
• Unlike the Mendeleev's periodic table, the elements in the modern Periodic table that are placed vertically are known as ," Groups" ,while,the one that are placed horizontally are called ,"Periods".