Modern Periodic Table

For many of us, the periodic table is a symbol of chemistry. The table is the tabular arrangement of elements and a great source of information about chemistry. A modern periodic table is built on the current periodic law, which states the physical and chemical properties of the elements are the periodic functions of their atomic numbers. The table is an arrangement of factors that increase their atomic numbers from left to right across each row. The modern periodic table consists of 7 horizontal rows and 18 vertical columns arranged in a tabular form.

History of Periodic table

Dmitri Mendeleev framed the modern periodic table in 1869; while travelling by train, Mendeleev noticed that some elements exhibited similar properties. Still, he also saw plenty of anomalies to the emerging patterns.

Antoine Lavoisier was the 1st scientist to classify elements based on their properties in 1789 before Mendeleev. He even arranged the elements into metals, nonmetals, gases, and earthly elements.

Many decades passed, and Johann Döbereiner attempted to group elements based on similarities in chemical properties in 1829. Finally, after three decades and 6 yrs, i.e., 1865, an English Chemist, John Alexander Newland, arranged the elements in the order of their increasing atomic weights and showed the physical & chemical properties of the 8th element are similar to the 1st element.

Then in 1869, Mendeleev categorised the elements based on their atomic masses and arranged them into horizontal rows called periods and vertical columns called groups. He was successful in arranging 63 elements.

Mendeleev’s Periodic Table

Significance of Mendeleev’s Periodic Table

• Systematic study of the elements

Mendeleev’s periodic table is systematised and simplified based on the study of elements and their compounds. Thus, knowing the properties of one element in a group, the other elements’ properties can be predicted.

• Prediction of new elements

When Mendeleev’s periodic table was formulated, there were only 56 elements that were known. Therefore, while arranging the elements according to their properties, Mendeleev’s left some blanks, spaces, or gaps. These gaps represented unknown elements. Mendeleev the properties of these unknown elements based on their positions, for example, Gallium and Germanium.

• Correction of doubtful atomic weights

With the help of Mendeleev’s periodic table, there were some doubtful atomic weights to some elements, which were corrected. Ex: Beryllium.

Defects in Mendeleev’s Periodic Table

• The unnatural position of hydrogen

Hydrogen is placed in group IA. However, it resembles the elements of both group IA (alkali metals) and group VII A (halogens).

• Anomalous pairs of elements

Some elements have a higher atomic weight, which precedes the lower atomic weight. Ex: Argon (at. Weight: 39.9) precedes Potassium (at. Weight: 39.1).

• Position of isotopes

Isotopes are atoms that have the same element having different atomic weights. According to Mendeleev’s periodic table, these are classified and placed at various places in the periodic table according to their atomic weights.

• Dissimilar elements are grouped, whereas similar are placed differently

Alkali metals such as lithium, Sodium, Potassium, etc. (group IA) are placed in the same group as the coinage metals like Silver, Copper and Gold (group IB) even though they differ drastically in their properties.

Features of Modern Periodic Table

The modern periodic table is an organised form of table to provide great deal of information about elements and to predict the properties not been discovered yet.

The modern periodic table has the following features:

• Elements arranged in ascending order are grouped as per their atomic numbers.
• The table is grouped into two ways, i.e., periods arranged in horizontal rows that are 7 in number and vertical columns called groups 18 in number.
• We move from top to bottom in a group where elements show similar physical and chemical properties. They contain the same number of outer electrons, which offer a gradual change.
• As we move from left to right in a period, there is a gradual change in properties and a decrease in atomic size. 
• Mendeleev’s periodic table, which consists of 63 elements, presently has 118 elements, whereas the modern periodic table consists of more elements.

Elements Classification in the Modern Periodic Table

The elements in the modern periodic table are classified under the following:

• Alkali and Alkali earth metals: In group 2, there are six chemical elements of the periodic table, including beryllium, magnesium, calcium, strontium, barium and radium. These elements have similar properties, all silvery-white, shiny and reactive metals. They tend to release their two valence electrons, achieving a full outer energy level. They thus achieve the most durable and stable arrangement of electrons.

• Transition Metals: The electrons that can participate in chemical bonds—in two shells instead of only one. They occupy the middle portions of the modern periodic table periods. The elements here are metals that are strong, hard, and lustrous. These elements also have high melting and boiling points and are good conductors of heat and electricity. Ex: Titanium, Nickle, Zinc, Iron, etc.

• Metalloids and nonmetals: The elements that border the stair-stepped line in the modern periodic table are classified as Metalloids. These have properties that are somewhat of a cross between metals and nonmetals. Ex: Boron, Silicon, Germanium, Arsenic, etc.

• Noble Gases: These are placed in the 18th group of the modern periodic table and have filled valence shells. Ex: Helium, Argon, Radon, Neon, etc.

Classification of Periodicity

1. All the elements of group 1, i.e., alkali metals, have a similar outer electronic configuration, ns1
2. In the same way, the elements of group 17 have a similar external electronic configuration, ns2 np5.
3.  The elements of group 18 have an outer electronic configuration of ns2 np6.
4. Elements in a group have similar properties to those of all the other members of the same group.
5. Based on the entry of the valence electrons in the respective sub-shell, the periodic table is divided into s, p, d, and f blocks.

Conclusion

• The modern periodic table organised the elements, which are arranged as per their increasing atomic numbers.
•  In the modern periodic table, every element is represented by a chemical symbol.
• There are rows in the periodic table, which are known as Periods.
• There are columns in the periodic table, which are known as Groups.
•  All elements are classified into three classes, i.e., metals, metalloids, or nonmetals.
•  In the modern periodic table, the total number of groups is 18.
• Mendeleev’s periodic table orders the elements based on their atomic mass, whereas the Modern periodic table orders them based on their atomic number.