# Periodic Table

Understanding Periodic Table: A shopkeeper dealing in different items say stationary, cosmetics, confectionery, etc. place things of one type at one place. In the library, books on one subject are placed in one almirah. This is done for convenience and to make things easy and simple.

Similarly, a total of 118 natural and synthetic elements are known. These elements have different physical and chemical properties and they combine with one another to form millions of compounds each having different properties. It becomes difficult to study the properties of elements and their compounds individually because of their vast number. So there is a need of a modern long form of table.

## What is Periodic Table?

Periodic Table is one in which all the known elements have been arranged on the basis of their properties in such a way that elements with similar properties have been grouped together in the same vertical column and dissimilar elements are separated from one another.

## History of the Periodic Table

In order to study elements in an organized manner, they need to be classified.

1. Dobereiner, a German chemist, grouped the elements in triads (groups of three elements), in such a way that
 The middle element of the triad had both atomic mass and properties roughly equal to the average of the other two elements of the triad.
• Examples: Ca (40), Sr (88), Ba (137): Average of Ca and Ba is equal to= Sr (88.5)
•  Li (7), Na (23), K (39) : =Average of Li and k is equal to= K (23).

However, this method was soon discarded, since only a few elements known at that time could be arranged in such triads.

2. Newland, an English scientist, gave the law of octaves, which states that:

 When elements are arranged in an increasing order of atomic mass, every eighth element beginning from any element resembles the first element in its physical and chemical properties.

This method was also discarded since it failed to accommodate the heavier elements.

3. Dmitri Mendeleev, a Russian chemist published a table of elements, which states that

 The properties of elements are the periodic functions of their atomic masses.

He even predicted the existence of those elements which were not discovered at that time. The whole table arrangement in vertical columns known as groups and horizontal rows are known as periods. He arranged the elements in order of their increasing atomic masses.The table could not explain the trend in atomic mass change. Mendeleev again published a new table of elements which is divided into 4 blocks. This table is called as long form of a table.

## Development of the Periodic Table

Attempts have been made from early times to develop and classify the known elements so as to make the study of chemistry simpler, systematic and interesting. This leads an easy way to study properties of elements and their compounds. Thus, instead of studying each of 118 elements individually, it is much more convenient to study them into a few broad groups.

## How to Read the Periodic Table?

We can study the properties of elements in two ways: one divide it into blocks and second considering periods and groups. The following is a study with groups and periods.

Must Read: Table blocks

Periods

### First period

This period is the shortest period. The first period has 2 elements hydrogen (1s1) and helium (1s2) only. In their case, the first shell K is completed. Here n = 1.

### Second period

It contains the eight elements and termed as short period.The second period starts with n = 2, the first member is lithium and the shell (L) is completed at Neon.

### Third period

Similarly, the third period (n = 3) starts with sodium (Z=11) and is completed at argon (Z=18). This period also contains the 8 elements.It is also called as a short period.

### Fourth period

This period called as long period. It contains 18 elements with Z = 19 to 36. The fourth period (n = 4) starts with potassium and ends with Krypton but has 10 more elements than the 3rd period. It has total 18 elements.

### Fifth period

The fifth period (n = 5) is similar to the fourth period and has 18 elements in all. It starts with rubidium and ends with xenon.

### Sixth period

The sixth period (n = 6) has 32 elements in which the filling up of electrons takes place in 6s, 4f. 5d and 6 p orbitals respectively from Cs to Rn. Filling up of the 4f orbitals begins with cerium (Z = 58) and ends at lutetium (Z = 71) to give the first f transition series called Lanthanide series.

### Seventh period

This seventh period (n = 7) would be similar to the sixth period but is incomplete and contains only 19 elements from Fr to Ha. It includes most of the man-made radioactive elements. Filling of 5 f orbitals after actinium (Z = 89) gives the second f transition series known as the actinide series.

Groups

The vertical columns are called as groups. There are 18 groups in total.

For the knowledge of Groups read the following subtopic:

## Periodic Table Symbols

Symbols are given with atomic number.

## Electronegativity Periodic Table

• The value of electronegativity found to be maximum in fluorine and minimum in cesium.
• Electronegativity is generally measured with the help of the Pauling scale.
• Electronegativity has a great impact on the type of bond chemical bonding.
•  Read more: Electronegativity.

## Periodic Table Trends

Periodic trends change both for period and group. In a period while moving from left to right and in a group while moving from top to the bottom of the table.

## Periodic Table Families

Elements which show similar properties are placed in their respective groups. The classification of groups of elements means an arrangement in which similar elements are put together while dissimilar elements are separated from one another.

• Alkali metals.
• Alkaline earth metals.
• Halogen family
• chalcogen family
• inert element family
• Lanthanide Family
• and actinide families

are some of the periodic table families.

## Metals on the Periodic Table

Except for p block, the s, d and f block elements in the long form table are metals. Their metallic character decrease moving left to right and increases moving top to down. The elements are present on the left side are metals.

## Modern Periodic Table

In the year 1913, an English physicist, Henry Moseley, a young physicist from England, studied the frequencies of the X-rays which were emitted when certain metals were bombarded with high-speed electrons. He found that in all the cases, the square root of the frequency (v) was directly proportional to the atomic number of the atom of the metal.

These studies led Moseley to believe that instead of atomic mass, atomic number is the fundamental property of an element. In the light of the above observations, Moseley gave the modern periodic law which states that:

 Physical and chemical properties of the elements are the periodic function of their atomic number.

The elements with a different electronic arrangement of the atoms possess different chemical properties. As the number of electrons in an atom is given by the atomic number and not by the mass number, therefore, the atomic number should form the basis of the classification of the elements in the long form of table and not atomic mass as predicted by Mendeleev.

## Periodic Table Facts

• No such elements in the periodic table which start with J letter.
• Carbon having atomic 6 has the only elements that have the tendency of forming millions of compounds in the world of chemistry.
• Atomic no 87 francium is the rarest element on earth.
• Scientists discover the helium element when observing the sun carefully.
• Properties of elements in the modern long-form table are based on the electronic configuration.

## Parts of the Periodic Table

• Alkali metals.
• Alkali Earth Metals
• Transition metals
• Non metals
• Metalloids
• Inert or Nobel gases
• Lanthanide elements
• Actinide elements

## Periodic Table Properties

The few defect left behind in the table of elements were removed by Henery Mosley. He put forward the modern periodic table and states that the properties of elements are a periodic function of their atomic number. Important features of the modern long form table are listed below:

• It is based upon the atomic number which is the most fundamental property of the element.
• The position of an element in the table is related to the electronic configuration of the elements.
• It is simple and easy to reproduce.
• The elements present in any vertical column resemble closely with one another.
• Division of the elements has helped to understand their properties easily.
• The properties of the elements in periodic table blocks can be predicted even before their discoveries.
• It reflects the similarities, differences, and trends in physical and chemical properties more clearly. Thus it is an ideal arrangement for the classification of the elements.
• There is no need for providing a separate place to isotopes of the elements as they have the same atomic number.
• The position of the transition elements is justified in the light of their electronic configuration. These elements have their penultimate shell incomplete.

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