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Modern Periodic Table: Modern Periodic Law, Periodicity, Periodic Classification of Elements, Long Form of Modern Periodic Table

I have been trying for ages to make an authentic mango pickle that would taste the same as that made by my great-grandma!

After a long period of trying and testing out the different recipes for pickles, I could finally come up with the best version of mango pickle that suits the universal appetite! Well, the path was not easy, but patience has its yummiest results!

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Similarly, it was not a shortcut path that led to the development of our modern periodic table. After a long period of trying out various models and theories of obtaining a regularised pattern in between elements and trying to arrange them in an orderly fashion, finally evolved the Modern Periodic table, our very own chart-friend! 

 

The modern periodic table is a new and improved version of certain modified versions put forward by scientists, especially Mendeleev, in the 19th century. Dimitri Mendeleev, popularly acclaimed as the father of the periodic table, put forth the first iteration of the periodic table similar to the one we use now. 

The development of various atomic models and advances in quantum theory revealed that the atomic number is the most basic property of a chemical element.

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TABLE OF CONTENTS

Modern Periodic Law 

  • The modern Periodic law can be stated as “The physical and chemical properties of the elements are periodic functions of their atomic numbers.”
  • The physical and chemical properties of the elements are the periodic functions of their atomic numbers which correspond to the number of electrons or protons in a neutral atom.
  • The periodic variation in electronic configurations, which controls how an element and its compounds' physical and chemical properties are expressed, is very naturally what led to the development of the Modern Periodic Law.
  • The Periodic Law exposed important analogies among the 94 naturally occurring elements (neptunium and plutonium, like actinium and protactinium, are also found in pitchblende – an ore of uranium). Elements with atomic numbers from 95 to 118 have only been synthesised in laboratories or nuclear reactors. 


You may also want to learn about isotopes and isobars.

Periodicity and its Significance

  • When the elements are placed in the periodic table in increasing order of atomic number, a pattern known as periodicity emerges in their physical and chemical characteristics. It reflects the modern periodic law.
  • Examples of periodic properties include atomic radii, ionisation energy, electron gain enthalpy, electronegativity, melting and boiling points etc. 
  • The periodicity is due to the similar outer electronic configuration of elements after certain regular intervals. 
  • Example: Elements of group 1 i.e., alkali metals, have a similar outer electronic configuration i.e.ns1. Here ‘n’ refers to the principal quantum number of the outermost shell. Similarly, elements of group 17 (halogens) have similar outer electronic configurations, ns2np5. Hence, have similar properties to one another due to the presence of 7 valence electrons. 

 

Yom may also want to learn about the electronic configuration of iron.

Long Form of the Modern Periodic Table 

  • The periodic table is a systematic arrangement wherein all the elements known to man are organised according to their increasing atomic number and recurring chemical properties
  • In the modern periodic table, horizontal rows are called periods and the vertical columns are called the groups. They are arranged in a tabular arrangement wherein a row is a period and a column is a group.
  • Here is a GIF showcasing the groups and the periods in the modern periodic table.

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FIG: Groups in the Modern Periodic Table

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Periods in the Modern Periodic Table

Main Features of the Long Form of Modern Periodic Table: 

  • Elements in the modern periodic table are arranged in the increasing order of their atomic numbers (Z).
  • We have a total of horizontal rows or periods, and 18 vertical columns, also known as groups.
  • Elements having similar outer electronic configurations are arranged in the same vertical columns, referred to as groups.
  • The principal quantum number ‘n’ decides the period of the element. Each period corresponds to the highest principal quantum number (n) of the elements in the period.
  • The principal quantum number (n) is one of the four quantum numbers (n, l, m, and s). For example, if n = 3, then it indicates the principle shell as 3.
  • Elements are arranged from left to right in the order of their increasing atomic numbers.
  • Elements in the same group will have the same valence electronic configuration and hence, similar chemical properties.
  • Whereas, elements in the same period will have an increasing order of valence electrons. Therefore, as the energy level of the atom increases, the number of energy sublevels per energy level increases.
  • The valence shell electrons correspond to the group number of an element.
  • The first period contains 2 elements. The subsequent periods consist of 8, 8, 18, 18 and 32 elements, respectively. 
  • In this form of the Periodic Table, 14 elements of both the 6th & 7th periods (lanthanoids and actinoids, respectively) are placed in separate panels at the bottom. 

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Periodic Classification of Elements in Modern Periodic Table

Classification of elements in the periodic table can be done in four ways based on their electronic configurations:

Noble Gas Elements

  • The elements of Group 18 are called noble gases or inert gases.
  • The electronic configuration of the first element (helium) of this group is 1s2. Rest all the elements (neon, argon, krypton, xenon, and radon) have their outer shell electronic configuration as ns2 np6.
  • Their outermost shell is completely filled. Due to the completely-filled electronic configuration, they generally do not react with the other elements.

Representative Elements

  • The elements of groups 1, 2, 13, 14, 15, 16, and 17 are known as the main group elements or normal elements. They are termed representative elements. 
  • They consist of the elements of the s-block (Group 1 & 2) and p-block (Group 13 - 17).

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Transition Elements

  • The elements of groups 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 are known as the transition elements.
  • They have their outer shell electronic configuration as (n-1)d1-10 ns1-2 and are referred to as transition elements. These elements are also known as the d-block elements. A block is a set of adjacent groups in the periodic table.

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Inner Transition Elements

  • Lanthanoid and actinoid series of elements, which fall at the bottom of the periodic table, are termed inner transition elements.
  • In these elements, the 4f and 5f orbitals are partially filled, rendering them special properties.  
  • In the case of lanthanoids and actinoids, the last electron added to each element is filled in the f-orbital. These two series of elements are known as the inner transition elements as these are present between transition elements. They are also known as f-block elements.

Practice Problems (H3 format) on Modern Periodic Table

Question1.  According to the modern periodic law, the physical and chemical properties of an element are the periodic function of its:

A. Atomic Volume 

B. Atomic Mass

C. Atomic Number

D. Ionic radii

Answer: As per the modern periodic law, the physical and chemical properties are the periodic function of its atomic number.

Question2. The period number of any element corresponds to its highest:

A. Azimuthal Quantum number

B. Principal Quantum Number 

C. Magnetic Quantum Number

D. Spin Quantum Number

Answer: Principal quantum number corresponds to the number of shells of an atom and it is represented by and the highest value for an element corresponds to the period number of an element.

Question3.  How many elements does the shortest period consist of?

A. 2

B. 4

C. 8

D. 6

Answer: Shortest period is the first period having two elements i.e., Hydrogen and Helium.

Question4.  How are the elements in the periodic table arranged?

A. Increasing atomic weight

B. Increasing atomic number

C. Increasing order of density

D. Increasing order of number of neutrons

Answer: Increasing atomic number forms the basis of the modern periodic table.

Question5. Who gave the modern periodic law?

A. Mendeleev

B. Moseley

C. Lothar Meyer

D. Newland

Answer: Moseley was the first person to determine the relation between characteristic properties of elements relative to their atomic number. Hence, he created the basis of the modern periodic law.

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FAQ's on Modern Periodic Table

Question1. Who gave the modern periodic law?

Answer: In 1869, Dmitri Mendeleev and Lothar Meyer established the periodic law independently, but both defined periodicity in terms of atomic mass. It was Moseley, who observed regularities in the characteristic X-ray spectra of the elements when their frequencies were plotted against their respective atomic number. So the modifications done in the periodic law in modern times (i.e, the physical and chemical properties of the elements are periodic functions of their atomic numbers) can well be attributed to Moseley.

Question2. How do periodic trends relate to periodic law?

Answer:  Periodic trends give similar patterns in the periodic table showing us the various aspects of an element such as electronegativity, atomic radius, or ionising power. The periodic law tells us that when grouped by atomic number, certain properties of elements occur periodically.

Question3. How many periods and groups are there in a modern periodic table?

Answer: According to the modern periodic table, the elements are organised in increasing order of atomic number, and there are a total of 18 groups and 7 periods. There are 2 elements in the 1st period, 8 elements each in the 2nd and 3rd period, 18 elements each in the 4th and 5th period, and 32 elements in the 6th period and 7th period.

Question4.  Who discovered Element with atomic number 118?

Answer: 118th element was named after a Russian-Americal nuclear physicist Yuri Oganessian who is pioneer in the discovery of synthetic elements. The name of this element was given on his name i.e., oganesson (Og).

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