Introduction to Modern Periodic Table
It is indeed true that for many of us the picture of a periodic table is the symbol for chemistry. The periodic table is not just an organised tabular arrangement of elements but the greatest source of information as far as chemistry is concerned. Without a proper classification and arrangement of elements, it would have been really complicated to study and explore the plethora of possibilities in chemistry. It is really fascinating to know how the periodic table was invented.
History of the Periodic Table
The periodic table that we study today is the modern periodic table and was invented by Dmitri Mendeleev. However, Mendeleev was not the first one who grouped and arranged the elements in the form of a periodic table. The following are a few attempts to classify elements that took place prior to the recognition of the modern periodic table.
In 1789, Antoine Lavoisier was the first to classify elements based on their properties. He grouped the elements into gases, non-metals, metals and earthly elements.
After several decades, in 1829 Johann Döbereiner made an attempt to group elements. Based on the similarity in chemical properties, he grouped elements into triads. The middle element’s atomic weight in the triad stands approximately as the average of the first and third elements’ atomic weights. This can also help define the properties of the middle element. Eg: Lithium, sodium and potassium. Since Döbereiner failed to classify all known elements into triads, the law of triads did not find success.
The attempt to classify elements did not stop here and it was in 1865 that the English Chemist John Alexander Newland arranged the elements in the order of their increasing atomic weights. He discovered a periodic pattern in the arrangement. He showed that the physical and chemical properties of the eighth element is similar to the properties of the first element in that row. This generalization made by Newlands is known as the 'Law of Octaves'.
It was only in 1869 that Mendeleev published his paper in the Journal of Russian Chemical Society where he classified the elements based on their atomic masses and arranged them into horizontal rows called periods and vertical columns called groups. The periodic law states that the properties of elements are a periodic function of their relative atomic masses. Mendeleev was successful in arranging all 63 elements that were known in his time into a tabular form which contained eight columns and seven rows. It also contained some gaps which were later filled after the discovery of new elements.
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Mendeleev was successful in classifying the elements and showing the periodic similarity in elements. However, there were a few anomalies in the arrangement which were later cleared by the English Physicist, Henry Moseley.
Moseley's Periodic Law
Henry Moseley showed that the chemical and physical properties of elements are determined by the atomic number and not by the atomic mass. He restated the periodic law as-
'Physical and chemical properties of an element are a periodic function of its atomic number.'
Moseley's periodic law is also known as the Modern Periodic Law and it paved the way to the modern periodic table.
Modern Periodic Table:
The modern periodic table of elements is the one that we use today. It is based on the concept of Mendeleev's periodic table but differs in the fact that the elements are arranged in the increasing order of atomic number and not atomic mass.
Features of Modern Periodic Table
In the study of chemistry, the modern periodic table holds prime importance. Following are some of the main features of the modern periodic table.
Elements are grouped in ascending order of their respective atomic numbers.
There are seven horizontal rows called periods and eighteen vertical columns called groups.
The elements in a group show similar physical and chemical properties since they contain the same number of outer electrons. But they show a gradual change as we move from top to bottom in a group.
The elements in a period show a gradual change in properties on moving from left to right. Atomic size gradually decreases as we move from left to right.
The modern periodic table consists of more elements when compared to the 63 elements in Mendeleev's periodic table. Presently it has 118 elements.
It would not be wrong to say that the study of the chemistry of elements would have been impossible without the existence of the modern periodic table. The classification of elements in the modern periodic table helps in the easier understanding of the properties of elements.
Classification of Elements in the Periodic Table
Following are the major classification of elements in the modern periodic table-
Alkali and Alkaline Earth metals: The first two groups on the left side of the periodic table consist of highly reactive elements (except hydrogen). The first group elements contain one electron in the valence shell while the second group elements contain two electrons in their valence shell.
Transition metals: These elements occupy the centre of the periodic table and mostly show the properties of metals. The elements starting from group 3 to 12 fall under transition metals. Some of the transition metals are placed separately in two rows at the bottom of the periodic table. These are known as Lanthanides and Actinides.
Metalloids and nonmetals: Metalloids generally appear in a diagonal line at the right side of the periodic table. These are basically the elements that separate metals on the left side of the periodic table from the nonmetals on the right side of the periodic table. These elements exhibit the properties of metals and non-metals, thus, they are called metalloids.
Noble gases: The extreme right side of the periodic table is occupied by gases. They are placed in the 18th group and have completely filled valence shells. These gases are non-reactive and are called the inert or noble gases.
The study of modern periodic table (groups and periods) is so significant in the world of chemistry that it can be called as the pillar of che
Modern Periodic Table - Features & Significance
A modern periodic table is a table consisting of elements that we still use in the present time. The table is based mainly on the periodic table of Mendeleev but has some differences. The elements here are arranged in the order of increasing atomic number and not atomic mass like the previous tables. Some of the features we should know about this table are:
The constituents of the table are arranged in the increasing order of their atomic number.
The table has 7 rows that are horizontal and are called the rows. Similarly, there are vertical columns that are 18 in number and called the groups.
The properties like physical and chemical are similar for all the elements present in the table. In the outer electrons, they have the same number but gradually change from the top to the bottom of the group of elements.
The elements present in the period change gradually when we move from left to right. The atomic size also decreases from the left to right direction.
This periodic table has more elements compared to the previous table like Mendeleev’s periodic table. It has about 118 elements.
Without the modern periodic table, it would have been hard to study all the elements that are required today. From the classification of these elements, we can understand the properties of the elements. Thus, the table provides a huge help to us in the present day.
Position of Elements in the Modern Periodic Table
In 1869, 63 atoms were discovered. Mendeleev classified the atoms in a table called Mendeleev's periodic table in the form of periods and groups. Mendeleev created the framework of the modern periodic table, having the same distribution as the Mendeleev periodic table. The Mendeleev periodic table is based on the increasing atomic mass, whereas the modern periodic table is based on the increasing atomic number.
Firstly, atomic mass depends upon the number of protons and the number of neutrons collectively. But the atomic mass is based on the proton and neutron, which is not the basic unit, whereas the atomic number is just based on the number of electrons which depends upon the increasing number of electrons. The atoms are placed in the modern periodic table on the basis of the increase in the number of electrons.
Explain the Position of Hydrogen in the Periodic Table
Mendeleev classified the atoms on the basis of the increasing atomic mass. Before Mendeleev's periodic table, Newland’s Classification was known as Newland’s Octave Law. Newlands octave law is based on the musical rhythm that the properties of the first and eighth atoms will be the same. Mendeleev rejected Newland's Octave Law in 1869 and discovered a periodic table based on atomic mass and chemical properties.
In the modern periodic table, 118 atoms are classified in the form of 7 periods and 18 groups. Along the period, there is a change in the chemical properties from metal to metalloids and then metalloids to non-metal. Down the group, the chemical properties are the same for all the atoms in the group.
Here, Hydrogen atoms have one electron in the valence shell, having one proton and one neutron. The hydrogen atom has the properties of metal and non-metals. Hydrogen has no fixed position in the periodic table. Hydrogen can act as an alkali metal or nonmetal.
There are two periods placed away from the periodic table because of the different properties of the atoms present in the periodic table, as these atoms are radioactive. Both groups are called Lanthanides and Actinides, respectively.
Main Features of Modern Periodic Table
The modern periodic table is a big jump from the Mendeleev periodic table. The modern periodic table has many salient features.
The atoms are placed in the periodic table on the basis of the increasing atomic number, which is based on the number of electrons.
The atoms are classified in the form of 7 periods and 18 groups which represent the change in the chemical and physical properties in the table.
Along the periods, the chemical periods and physical properties of the atoms changes. As the properties change from metal to metalloids and then to non-metals
In the groups, every group shows the same property down the group. Group I are alkali metals, and Group XVII are halogens.
The properties, such as the presence of isotopes, can be explained by the modern periodic table as it is based on the atomic number.
Periodic Table Colour Coded
The modern periodic table uses colour coding to distinguish the properties of the atom in the table. As the colour code is to show the metals, which are shown in purple in the above image of the periodic table. Similarly, the blue colour shows the metalloids, which have the property of metals and non-metals. The non-metals are shown by the transition colour of orange to green to yellow.
There are two other groups, light green and red, showing lanthanides and actinides.
Key Features
The horizontal columns are called Periods, and the vertical columns are called Groups.
Metalloids are elements consisting of the property of metals and non-metals.
Atomic mass can be defined as the mass of the atom, which is equal to the twelfth part of the mass of the carbon atom.
The Mendeleev periodic table was firstly classified on the basis of 7 periods and 8 groups, whereas the modern periodic table consists of 7 periods and 18 groups.
Isotopes can be defined as atoms which have similar protons and different numbers of neutrons. The atomic number is the same, but the atomic mass is different.
Interesting Facts
Carbon is an element which is present in many forms, which are called allotropes. The allotropes of carbon are Diamond, the hardest element in the world.
Sodium and potassium are solid elements which can be cut by a knife. Sodium is kept in kerosene because it catches fire.
There are elements which are radioactive and produce radiation that can be harmful and useful at the same time as they can power a whole city.
FAQs on Modern Periodic Table
1. How were elements classified in the modern periodic table?
The elements of the modern periodic table are as follows:
There are alkali and alkaline earth metals which are present on the left side of the periodic table and have elements that are highly reactive. The elements of the 1st group have one electron in the valence shell and the elements of the 2nd group have two electrons.
There are transition metals that occupy the periodic table’s centre and show the properties of the metals. They start from 3-12. Some of them are also placed separately in the bottom two rows and are named as lanthanides and actinides according to their properties.
There are metalloids and nonmetals. Metalloids are present diagonally in the right side of the table and differ from the non-metals present in the right side. They express both the properties of nonmetals and metals and are so named.
Lastly there are noble gases which are present at the extreme right of the table. They are the 18th group and have filled valence shells and have properties like non-reactivity.
2. What were the achievements in Mendeleev’s Periodic Table?
The achievements made by Mendeleev’s were as follows:
Elements that had similar properties were placed in the same group that made a systematic way to study elements.
He corrected the atomic masses of many elements after placing them correctly. Atomic masses of elements like gold, platinum and indium were corrected.
The prediction of elements that were yet to be discovered was arranged in the same group and these elements were later named scandium, germanium and gallium.
He placed the noble gases correctly in a new group and this was done without disturbing the order that already existed.
3. What were the demerits of Mendeleev’s table?
Some of the limitations or demerits of Mendeleev’s table are as follows:
He couldn’t justify the position of hydrogen which showed both alkali and halogen characteristics.
The atomic weight of the isotopes is not the same but they were placed in the same positions together.
Some of the elements paired had anomalies. The element cobalt was placed before the nickel even when it had a higher atomic weight.
Some of the similar elements were placed in different areas. For example, platinum and gold.
He couldn’t give an explanation to the periodicity of the elements.
4. What are Dobereiner’s Triads?
Scientist Dobereiner took three elements that had similar properties and grouped and arranged them in the order of increasing atomic masses. He named this group triad. With this experiment, he showed that the atomic mass of the element present in the middle has the arithmetic mean of the other two elements approximately.
5. What did Newland assume for his octave rule?
The assumptions made by Newland for his octaves are as follows:
He stated that the octave can be applied for elements that have atomic mass lower than 40.
Properties of the newly discovered elements did not fit the Octaves’ rule.
Newland also placed two elements in the same area so that the slots can be fit in the table.
He put elements with no similar properties in the same area.
6. What do you mean by the atomic mass unit?
Firstly, Hydrogen is taken as the reference for finding the mass of the multi-electron atoms. The atomic mass unit can be defined as the mass of the 12 parts of the carbon having atomic mass 12. The atomic mass unit can be designated as amu or um (unit mass).
7. What are the drawbacks of Newland’s octave law?
Newland’s octave law describes that the chemical and physical property of the first atom is similar to the eighth atom of the table. This law is based on the musical rhythm. The drawback of Newland's octave rule was that the newly discovered atoms do not have the same property as its eighth atom. There are contradictions between the properties according to the law, which gives rise to the Mendeleev periodic table.
8. What are the properties of the Modern periodic table?
The main drawbacks of the Mendeleev periodic table are the use of atomic mass as the basic unit to place the atoms in the table, giving rise to the modern periodic table. The properties of the modern periodic table are:
It uses the atomic number as the basic unit, which depends upon the number of electrons present in the atom.
The modern periodic table has vertical rows, which are called periods. The atoms in the period have the same properties.
There are also spaces left for the newly discovered atoms can fit easily.
