Imagine a bunch of books piled up in a room. Scattered here and there. It will be very tough to select a book which is of your taste and genre, right? But what if it is arranged in an order, novels on one rack, fantasy on the other. Fairy tales, science, mathematics, fiction etc each in separate section. It will be easier to choose what you need and say what type of book you need looking up on the rack in which it is arranged.
The same happens in chemistry where the rack is the periodic table and the books – the elements.
The periodic table is an array or tabular representation of the chemical elements, which is done according to the periodic law, which states that the properties of elements have periodic dependance on their atomic numbers (Z).
In the tabular arrangement, the rows are called as periods and the columns are called the groups. The elements which belongs to the same column exhibit similar properties. Due to the electronic configuration in the atoms, the elements represent trends. The non-metallic character or the property to hold its own electrons increases from left to right across a period and also from bottom to top along a group. And the metallic character or the property to share or surrender the electrons increases in the opposite direction.
The periodic table and periodic law is inevitable, and plays a vital role in modern chemistry. The periodic law is considered as one of the most important and fundamental discovery in 1800’s. Russian chemist Dmitri Mendeleev put forwarded the periodic law which connects the relation between atomic number and properties. He designed the modern period table with gaps, as those elements were not discovered that time, but predicted the properties of those elements which in future will fill the gaps. The periodic table at the time of formulating consisted of elements up to atomic number 94, and now it consists of 118 elements filling all first 7 rows. It is uncertain about the future design of the periodic table as new elements with unpredictable properties may be synthesized or discovered. Now in 118 of the known elements, 94 are naturally occurring of which 80 are stable, 3 undergo slow radioactive decay and 11 undergo quick disintegration. The rest 24 elements are artificial, and all are radioactive. Technetium was the first element to be made artificially. It is the lightest element that has only radioactive isotopes (none are stable). Most of the elements on the periodic table are metals. The alkali metals, alkaline earths, basic metals, transition metals, lanthanides, and actinides all are groups of metals.
The elements of group 1, 2, 13, 14, 15, 16, and 17 are known as the main group elements or normal elements. The elements of groups 3, 4, 5, 6, 7, 8, 9, 11 and 12 are known as the transition elements. Group 18 is called noble gases or inert gases. Their outermost shell is completely filled. Due to this stable electronic configuration, they generally don’t react with the other elements. The elements of period one will one shell, of period two will have two shells and such. The first period of the modern periodic table is the shortest period as it contains only two elements. The second period two and three consists of eight elements each and is known as short groups. Period four and five have eighteen elements and are known as the long group. In the modern periodic table, group number 3 of period 6 consists of the lanthanide series which are the rare earth elements. The radioactive elements (actinides) are present in group 3 of 7th period.
The groups and properties are as follows
- Group 1 – Alkali metals, forming strong alkali with water
- Group 2 – Alkaline earth metals, forming alkali but weaker than on group 1 elements
- Group 3 – Boron Family, With Boron as first member of the group, named likewise
- Group 14 – Carbon Family, The most important base or organic matter, the carbon is the 1st member of this group.
- Group 15 – Nitrogen Family, consisting of Non-metals and metalloids
- Group 16 – Oxygen Family, also known as Chalcogens
- Group 17 – Halogen Family, forming salts.
- Group 18 – Zero group, Noble gases or inert gases which are inert or stable under normal conditions. Their outermost shell is completely filled and therefore they do not react with other elements.
The learning of periodic table starts from class 8th and the chapter Periodic classification of elements in class X NCERT, literally unfolds the new world of arrangement of elements in order.