Introduction:
The periodic table is a table in which all of the known elements are listed. The table arranges the elements in order of increasing proton number to show the similarities of chemical elements. Therefore elements with structural similarities & atomic number are placed together. These elements can be placed into two different categories, metals & non-metals.
The early years of the 19th century witnessed a rapid development in chemistry. The art of distinguishing similarities and differences among atoms prompted scientists to devise a way of arranging the elements. Relationships were discerned more readily among the compounds than among the elements; thus, the classification of elements lagged many years behind the classification of compounds.
Development of the Periodic Table
It was in 1817 when Johann Wolfgang Döbereiner showed that the atomic weight of strontium lies midway between those of calcium and barium. Some years later he showed that other such “triads” exist (chlorine, bromine, and iodine and lithium, sodium, and potassium).
Another way of classifying the elements was later proposed by John Alexander Reina Newlands in 1864. He proposed that elements be classified in the order of increasing atomic weights.
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As a result of an extensive correlation of the properties and the atomic weights of the elements in 1869, Dmitri Inovich Mendeleev proposed the periodic law, which states that “the elements arranged according to the magnitude of atomic masses show a periodic change of properties.”
Mendeleev’s Version of Periodic Table
The rows 1 to 7 are called periods. The columns I A on the left to 0 on the right are known as groups. Elements with similar properties fall into vertical columns (groups) and horizontal rows (periods), which form the table. The columns in the table are called Groups. The elements in a group have the same number of electrons in their outer shell.
Arrangement of the Elements According To Groups
Group I A – The Alkali Metals
Group 1 elements are soft silvery metals. They react strongly with water. The further down the group you go, the more violent this reaction is. These alkali metals are usually stored under oil to protect them from moisture and oxygen. They all have one electron in their outer shells.
Group II A – The Alkaline Earth Metals
This group consists of all metals that occur naturally in compound form. They are obtained from mineral ores and form alkaline solutions. These are less reactive than alkali metals.
Group III A – The Aluminum Group
The elements in this group are fairly reactive. The group is composed of four metals and one metalloid which is boron.
Group IV A – The Carbon Group
This group is composed of elements having varied properties because their metallic property increases from top to bottom meaning the top line, which is carbon, is a nonmetal while silicon and germanium are metalloids, and tin and lead are metals.
Group V A – The Nitrogen Group
Like the elements in group IV A, this group also consists of metals, nonmetal and metalloids.
Group VI A – The Oxygen Group
This group is called the oxygen group since oxygen is the top line element. It is composed of three nonmetals, namely, oxygen, sulfur and selenium, one metalloid, (tellurium) and one metal (polonium)
Group VII A – The Halogens
This group is composed of entirely nonmetals. The term “halogens” comes from the Greek word hals which means salt and genes which means forming. Halogens group are called “salt formers”.
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Group VIII A – The Noble Gases
This group is composed of stable gases otherwise known as the non-reactive or inert elements.
The Transition Elements
The elements in the middle of the table are called transition elements.
They are all metals and so they are also called transition metals.
Summary
A. Development of the Periodic Table
1. Johann Wolfgang Döbereiner classified elements in sets of three.
2. Dmitri Inovich Mendeleev devised the first periodic table, which he used to predict three new elements. He proposed the”periodic law” which states that when elements are arranged in order of increasing atomic number, their properties show periodic pattern.
B. The Periodic Table and the Elements
1. The periodic table is composed of 7 rows or periods and 18 major groups or columns.
2. The elements are given symbols devised by John Jacob Berzelius. An element is named after its discoverer, place of discovery, first letter of the name of the element, first and the second letter for those having the same first letter and some are after their Latin names. The elements are grouped into Group A and B Group by the INTERNATIONAL UNION OF PURE AND APPLIED CHEMISTRY (IUPAC).
3. Elements in the periodic table are also grouped according to metals, non-metals and metalloids. Metals are lustrous, malleable and ductile. They are good conductors of heat. Metals are found on the left side of the periodic table. Nonmetals have a diverse set of properties. They are found on the upper right side of the periodic table. Metalloids or semimetals possess the properties of both the metals and the non-metals.
Conclusion
The Periodic Table of Elements supports Chemistry, as it explains periodic law and the significance of the rows and columns of the periodic table, including how to relate the position of an element in the table to its atomic number and atomic mass. Students’ comprehension of the significance of the table will be reinforced as they learn how to use it to identify metals, semimetals, nonmetals and halogens, as well as the relative sizes of ions and atoms. The program also outlines the physical and chemical qualities of the members of each group of elements from the alkaline metals to the noble gases.
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