Merits of the Modern Periodic Table

Chemists have always tried to arrange the elements in a way that reflects the similarities in their properties. The elements in the modern periodic table are listed in order of increasing atomic number (the number of protons in the nucleus of an atom). Previously the scientists tried to arrange the elements, using relative atomic masses. This was primarily due to the lack of development of the concept of atoms being made up of smaller subatomic particles (protons, neutrons, and electrons). Long before the concept of the atomic number was developed, the basis of the modern periodic table was well established and even used to predict the properties of undiscovered elements.

What is a Modern Periodic Table?

The modern periodic table arranges the elements according to their atomic numbers. "The properties of elements are a periodic function of their atomic numbers," according to the modern periodic law. 

This means that if elements are placed in tabular form on the basis of increasing atomic numbers, then the elements with identical properties will appear after regular intervals or periods. There is a periodicity in the electronic configurations of elements when elements are arranged on the basis of increasing atomic numbers. Periodicity in element electronic configurations leads to periodicity in element chemical properties. Similar chemical properties are shown by the elements having similar electronic configurations.

Explanation of Modern Periodic Law which is used to construct the Periodic Table.

Consider the electronic configuration of elements which are arranged on the basis of increasing atomic number. The elements are from lithium to neon and from sodium to argon. The electronic configuration of the respective elements is shown below.

Atomic Number	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18
Elements	Li	Be	B	C	N	O	F	Ne	Na	Mg	Al	Si	P	S	Cl	Ar
Electronic Configurations	2, 1	2, 2	2, 3	2, 4	2, 5	2, 6	2, 7	2, 8	2, 8, 1	2, 8, 2	2, 8, 3	2, 8, 4	2, 8, 5	2, 8, 6	2, 8, 7	2, 8, 8

• From the above table, it is clear that lithium has atomic number 3 and electronic configuration 2, 1, so it has 1 as its valence electron (outermost electron).
• So as the atomic number increases to 11, which is an atomic number of sodium and electronic configuration is 2,8,1, it has 1 as its valence electron. It means that both sodium and lithium has 1 as it's valence electron.
• It can be concluded that as the atomic number increases from 3 to 11, the electronic configuration is repeated from 2,1 to 2,8,1. So the properties of elements are repeated as the electronic configurations are repeated.
• Therefore, the significance of the modern periodic table is that it relates the periodicity in the electronic configurations of the elements to the periodicity in the properties of the elements.

So, in the periodic table, the elements are arranged in horizontal rows, on the basis of increasing atomic numbers. Under each element, all the other elements with the same number of valence electrons are placed. These horizontal rows of elements in the table are called periods. There are seven periods in the table. 

The elements in the periods have consecutive atomic numbers. The table's vertical columns are referred to as groups. There are 18 groups in the table. The elements in the group do not have consecutive atomic numbers. From the atomic number 57 to 71, the elements are called lanthanide series (as the first element is lanthanum) and from atomic number 89 to 103, the elements are called actinide series ( as the first element is actinium).

Properties of the Modern Periodic Table.

1. The atomic number of elements, which is the most fundamental property of elements, are used to create the modern periodic table.
2. The isotopes of an element are placed along with the parent element.
3. The reason for the periodicity in properties of elements is explained in the modern periodic table. It relates the periodicity in the properties of the elements to the periodicity in their electronic configuration. It says that the properties of elements are repeated at regular intervals since the electronic configurations of the elements are repeated at regular intervals.
4. The reason why elements in a group show similar properties but elements in different groups show different properties is explained by the modern periodic table. The elements in the table are organised according to their electronic arrangements. All elements with comparable electronic configurations are grouped together and exhibit similar characteristics. Elements with varying electronic configurations are grouped together and have varying characteristics.
5. There are no abnormalities in the arrangement of elements in the current periodic table.
6. The modern periodic table explains why the characteristics of elements are repeated after two, eight, twenty-eight, and thirty-two elements. Since 2, 8, 18 and 32 is the maximum number of electrons that can be accommodated in K, L, M and N shells of the atoms of the elements, so the electronic configurations of the elements are repeated after 2, 8, 18 and 32 elements. Now, since the electronic configurations of the elements are repeated after 2, 8, 18 and 32 elements, therefore the properties of the elements are also repeated after 2, 8, 18 and 32 elements. This fixes the number of elements in a period of the table.

Advantages of the Modern Periodic Table.

• The periodic table chart is used as a teaching-aid in chemistry in schools and colleges.
• If the position of an element in the periodic table is known, then it is easier to remember the properties of an element. For example, the element rubidium with atomic number 37, occurs in group 1. We know that the common elements of group 1 are sodium and potassium. So the chemical properties of rubidium will be similar to the properties of sodium and potassium.
• If the position of an element in the periodic table is known, then it can be predicted which type of compounds can be formed by the element. For example, if an element is on the left side of the table, it will be metal and hence form only ionic compounds. If an element is on the right side of the periodic table, then it will be a non-metal and can form ionic as well as covalent bonds.
• The lanthanides and actinides, which differ from other groups in their properties, are put at the bottom of the periodic table separately.
• Chemistry can now be studied in a systematic and simple way due to the periodic table. It serves as a memory aid. All of the elements have been classified into a few groups in the periodic table. Each group is made up of elements having similar characteristics. It is far more convenient to study the properties of a few elements out of each group than to study all of the elements individually.

Sample Questions.

Question 1: Which of the following elements belong to the same group? Element A has an atomic number is 5. Element B has an atomic number is 10. Element C has the atomic number 13.

Answer:

The elements which have same number of valence electrons (outermost electrons), belong to the same group of the periodic table.

The electronic configurations of the given elements are:

Element	Atomic Number	Electronic configuration
A	5	2, 3
B	10	2, 8
C	13	2, 8, 3

 Since element A and C have the same number of valence electrons, so elements A and C belong to the same group.

Question 2: The elements which belong to the left side of the periodic table form ionic compounds or covalent compounds?

Answer:

Since metals form ionic compounds only and if an element is on the left side of the periodic table, it will be a metal and hence the element will form only ionic compounds.

Question 3: Which of the following elements show similar chemical properties? Element A has an atomic number is 3. Element B has an atomic number is 11. Element C has the atomic number 9.

Answer: 

The elements which have same number of valence electrons (outermost electrons), show similar chemical properties.

The electronic configurations of the given elements are.

Elements	Atomic Number	Electronic Configuration
A	3	2,1
B	11	2, 8,1
C	9	2, 7

Since element A and B have the same number of valence electrons, so elements A and B  show similar chemical properties.

Question 4: Do magnesium and potassium show similar chemical properties or not?

Answer:

The elements which belongs to the same group, i.e., the elements which have same number of valence electrons (outermost electrons) shows similar chemical properties.

The atomic number of magnesium is 12 and atomic number of potassium is 19. The electronic configuration of these elements is.

Elements	Atomic Number	Electronic Configuration
Magnesium	12	2, 8, 2
Potassium	19	2, 8, 8, 1

Since magnesium has 2 valence electrons and potassium has 1 valence electron, which are not same. So, magnesium and potassium do not show similar chemical properties.

Question 5: How does the modern periodic table help as a memory aid?

Answer:

The modern periodic table helps as a memory aid, as all of the elements in the modern periodic table have been classified into a few groups. Each group is made up of elements having similar properties. It is far more convenient to study the properties of a few elements out of each group than to study all of the elements individually.