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• CBSE Class 11 Chemistry Notes

# Periodic Classification of Elements

The modern periodic table is based on Mendeleev’s periodic law and the periodic table. Mendeleev created his periodic table in the late 18th century. Scientists had no clue regarding the interior structure of the atom at the time. The advancement of quantum theory and the development of various atomic models revealed that the atomic number is the most fundamental property of a chemical element. This resulted in the modification of Mendeleev’s periodic law, now known as modern periodic law. Periodic law in modern times can be stated as follows:

Elements’ physical and chemical properties are periodic functions of their atomic numbers.

The atomic number is equal to the number of electrons or protons in a neutral atom. Scientists now had a clear understanding of quantum numbers and the electronic configuration of elements in the periodic table after learning about the fundamental unit of elements. After learning about the periodic law, chemists noticed an analogy between the 94 naturally occurring chemical elements. This analogy piqued people’s interest in the chemistry of these elements. Scientists created a variety of artificial elements. A new periodic chart based on modern periodic law was constructed by altering Mendeleev’s periodic table.

### Need for the Periodic Classification of Elements

Elements are the basic units that make up all matter in our surroundings. Earlier, only 31 chemical elements were discovered in 1800. Around 63 new elements were discovered in 1865. This necessitated the periodic classification of elements. There are presently 118 elements that we are aware of. Humans are responsible for the creation of some of the 118 chemical elements.

Classification of the Elements in the Periodic Table:

The elements in the periodic table can be classified in four ways based on their electronic configurations:

• Noble gas elements: Noble gases are elements in the modern periodic table’s group 18. The electronic configuration of this group’s first element (helium) is 1s2. The rest of the elements (neon, argon, krypton, xenon, and radon) have an ns2 np6 outer shell electronic configuration. Since the octet of these elements is complete, they are extremely stable.
• Representative elements: S-block and p-block elements are examples of representative elements. The elements in groups 1 and 2 are referred to as s – block elements (elements with 1s2 and 2s2 outermost configuration). Group 13-17 are known as the p-block elements (outermost configuration varies from ns2 np1 to ns2 np5).
• Transition elements: Transition elements are elements that belong to groups 3 to 12 and have an outer shell electronic configuration of (n-1)d1-10 ns1-2. These elements are also referred to as d-block elements.
• Inner transition elements: The inner transition elements are the lanthanides and actinides series, which are found at the bottom of the periodic table. The 4f and 5f orbitals are partially filled in these elements, giving them unique properties.

### History of the Periodic Table

The modern periodic table, which we are studying today, was invented by Dmitri Mendeleev. Mendeleev, however, was not the first to group and arrange the elements in the form of a periodic table. The following are a few attempts to classify elements prior to the discovery of the modern periodic table. Antoine Lavoisier was the first to classify elements according to their properties in 1789. He classified the elements into four groups: gases, nonmetals, metals, and earthly elements.

Döbereiner attempted to group elements in 1829. He classified elements into triads based on their chemical properties. The atomic weight of the middle element in the triad is roughly equal to the average of the atomic weights of the first and third elements. This can also aid in the definition of the properties of the middle element. For example, lithium, sodium, and potassium. The law of triads did not succeed because Döbereiner failed to classify all known elements into triads.

In 1865, John Newland arranged the elements in ascending atomic weight order. In the arrangement, he discovered a periodic pattern. He demonstrated that the eighth element’s physical and chemical properties are similar to those of the first element in that row. Newlands’ generalization is known as the Law of Octaves. Mendeleev did not classify the elements based on their atomic masses until 1869 when he organised them into horizontal rows called periods and vertical columns called groups. According to the periodic law, the properties of elements are a periodic function of their relative atomic masses. Mendeleev was successful in arranging all 63 known elements at the time into a tabular form with eight columns and seven rows. It also had some gaps that were later filled after new elements were discovered.

Mendeleev was successful in classifying elements and demonstrating their periodic similarity. However, the arrangement had a few flaws that were later discovered by the English physicist Henry Moseley. Henry Moseley demonstrated that the atomic number, not the atomic mass, determines the chemical and physical properties of elements. He restated the periodic law as follows: An element’s physical and chemical properties are a periodic function of its atomic number. Moseley’s periodic law, also known as the Modern Periodic Law, laid the groundwork for the modern periodic table.

### Modern Periodic Table

We currently use the modern periodic table of elements. It is based on Mendeleev’s periodic table concept, but the elements are arranged in increasing order of atomic number rather than atomic mass.

Features of Modern Periodic Table

• Elements are arranged in ascending order of their atomic number.
• There are seven horizontal rows referred to as periods and eighteen vertical columns referred to as groups.
• Because they have the same number of outer electrons, elements in a group have similar physical and chemical properties. They do, however, show a gradual change as we progress from top to bottom in a group.
• Moving from left to right, the elements in a period exhibit a gradual change in properties. As we move from left to right, the atomic size decreases gradually.
• When compared to Mendeleev’s periodic table, the modern periodic table contains more elements. It currently has 118 elements.

### Classification of Elements in the Periodic Table

Following are the major classification of elements in the modern periodic table-

1. Alkali and Alkaline Earth metals: The first two groups on the periodic table’s left side are made up of highly reactive elements (except hydrogen). The valence shell of the first group elements contains one electron, while the valence shell of the second group elements contains two electrons.
2. Transition metals: These elements are located in the centre of the periodic table and primarily exhibit metal-like properties. Transition metals are elements ranging from group 3 to group 12. At the bottom of the periodic table, several transition metals are grouped together in two rows. These are referred to as Lanthanides and Actinides.
3. Metalloids and non-metals: Metalloids are typically found in a diagonal line on the periodic table’s right side. These are the elements that separate metals on the left side of the periodic table from non-metals on the right. Because these elements have properties of both metals and nonmetals, they are referred to as metalloids.
4. Noble gases: Gases occupy the extreme right side of the periodic table. They belong to the 18th group and have fully filled valence shells. These non-reactive gases are known as inert or noble gases.

### Sample Questions

Question 1: Who gave the modern periodic law?

Dmitri Mendeleev and Lothar Meyer independently established the periodic law in 1869. Mendeleev created the first periodic table, which was quickly followed by Meyer. Each grouped the elements based on their mass and proposed that those properties reoccur on a regular basis.

Question 2: How do periodic trends relate to periodic law?

Periodic trends are common patterns in the periodic table that show us different aspects of an element such as electronegativity, atomic radius, and ionizing power. The periodic law states that certain properties of elements occur on a regular basis when they are grouped by atomic number.

Question 3: Is atomic mass a periodic property?

Nuclear mass falls from top to bottom and always increases from left to right. As the atomic number has been developed as the basis for organizing the elements on the periodic table, the atomic number will always increase from left to right and top to bottom.

Question 4: Which is relative periodic property?