Chapter 6, Problem 49A

(a)

Interpretation Introduction

Interpretation: The period in which most elements were discovered is to be identified.

Concept introduction:

The periodic table is a columnar structure that organizes different elements into groups based on how they behave. The most important contribution to the early development of the periodic table was provided by the Russian physicist Mendeléev. Of all the periodic tables that were produced, the Mendeleev periodic table was the most important.

Answer to Problem 49A

  $1801-1850$

Explanation of Solution

As shown in the graph, From $1801-1850$ year, around 28 elements were discovered which is the greatest number.

Thus, in period $1801-1850$ , most elements were discovered.

(b)

Interpretation Introduction

Interpretation: Contribution of Mendeleev’s work in the discovery of elements is to be explained.

Concept introduction:

The periodic table is a columnar structure that organizes different elements into groups based on how they behave. The most important contribution to the early development of the periodic table was provided by the Russian physicist Mendeléev. Of all the periodic tables that were produced, the Mendeleev periodic table was the most important.

Answer to Problem 49A

Mendeleev predicted elements and left gap.

Explanation of Solution

In Mendeleev's periodic table, the order of the elements was determined by their atomic masses. Only 63 elements were known at the time of Mendeleev's work. Mendeleev discovered a periodic relationship between the qualities of elements and atomic mass. He organized the elements according to increasing atomic mass. Elements with similar qualities fall into the same vertical columns of the periodic table when he grouped the elements in this way.

For the yet-to-be-discovered components, Mendeleev left some gaps. So, Mendeleev predicted properties of yet-to-be-discovered elements. Thus, if a new element is found, it can be added to a new group without upsetting any already existing groups.

(c)

Interpretation Introduction

Interpretation: Percentage of elements discovered by 1900 is to be calculated.

Concept introduction:

The periodic table is a columnar structure that organizes different elements into groups based on how they behave. The most important contribution to the early development of the periodic table was provided by the Russian physicist Mendeleev. Of all the periodic tables that were produced, the Mendeleev periodic table was the most important.

Answer to Problem 49A

  $\text{75}\text{.2}\%$

Explanation of Solution

Till 1750 15 elements were discovered

From 1751-1800 16 elements were discovered.

From 1801-1850 28 elements were discovered.

From 1851-1900 26 elements were discovered.

From 1901-1950 15 elements were discovered.

From 1951-2000 13 elements were discovered.

Formula for calculating the percentage is as shown,

  $\%=\frac{\text{elements discovered by 1900}}{\text{Total elements discovered}}\times 100$

Substitute values in the above formula:

  $\begin{array}{c}\%=\frac{\text{elements discovered by 1900}}{\text{Total elements discovered}}\times 100\\ =\frac{15+16+28+26}{15+16+28+26+15+13}\times 100\\ =\frac{\text{85}}{\text{113}}\times 100\\ =\text{75}\text{.2}\%\end{array}$

Thus, $\text{75}\text{.2}\%$ of elements were discovered by 1900.