3.9. Exercises

What is the basic theme of organisation in the periodic table?

The periodic table is organized based on the atomic number of elements. Elements are arranged in order of increasing atomic number, which reflects the number of protons in an atom’s nucleus. This arrangement shows that elements with similar properties recur at regular intervals, allowing chemists to predict the characteristics of elements based on their position in the table.

Think of the periodic table like a library cataloging books. Just as books are arranged by author or title, making it easier to find works by the same author, elements are categorized based on their atomic structure and properties, making it easier to find and understand chemical behavior.

Which important property did Mendeleev use to classify the elements in his periodic table and did he stick to that?

Mendeleev used the atomic mass of elements as the primary property for classifying them in his periodic table. He initially arranged the elements by increasing atomic mass and grouped them based on similar chemical properties. However, he later encountered issues where some elements did not fit this arrangement correctly. For example, he placed iodine (with a lower atomic mass than tellurium) in a group based on its chemical properties rather than strictly adhering to increasing atomic mass.

Imagine organizing a group of friends by their ages. At first, it may seem logical to line them up from youngest to oldest. But if one of your friends behaves more like someone significantly older than they are, you might decide to place them with that older group instead. Mendeleev faced a similar challenge with his classification system.

What is the basic difference in approach between the Mendeleev’s Periodic Law and the Modern Periodic Law?

The basic difference lies in how elements are classified. Mendeleev's Periodic Law was based on atomic mass, stating that the properties of elements are a periodic function of their atomic weights. In contrast, the Modern Periodic Law states that the properties of elements are a periodic function of their atomic numbers, reflecting the number of protons rather than the total mass of the atoms. This change was validated by research in atomic structure, such as Moseley's work identifying atomic numbers.

Consider how you might arrange a set of colored blocks. Mendeleev's arrangement would be like organizing by weight, where heavier blocks come first. In comparison, the modern approach would be like organizing the blocks in order of height, which provides a clearer understanding of their relations based on a specific physical property.

On the basis of quantum numbers, justify that the sixth period of the periodic table should have 32 elements.

The sixth period contains elements with principal quantum numbers n=6. Each principal quantum shell can hold a maximum number of electrons described by the formula 2n². For n=6, this means a maximum of 72 electrons theoretically can fit. However, due to the filling of the f-block elements (the lanthanides), the actual number of elements that appear is 32, as the filling order of sublevels modifies how space is allocated.

Think of a concert hall that can hold a specific number of seats based on sections (like_groups of elements in the periodic table). Each section (principal quantum level) can hold a certain number of people (electrons). While the concert hall might have an ideal maximum capacity, the setup and design might lead to certain areas filling up with specific arrangement patterns, resulting in the actual attendance being lower than that of the total capacity.