Periodic Classification of Elements (Part I)

Elements belonging to the 18^th group of the periodic table have fully filled last valence shell. So, they have zero valency.

Mendeleev's Periodic Law states that the properties of elements are a periodic function of their atomic masses. The modern periodic law uses atomic numbers.

Newlands' Law of Octaves arranged elements in increasing order of their atomic masses, noting that every eighth element had properties similar to the first.

Johann Wolfgang Dobereiner was the first to classify elements into groups of three, known as 'triads', based on their atomic masses, showing a relationship between properties.

The Modern Periodic Law states that the properties of elements are a periodic function of their atomic numbers, as established by Henry Moseley.

The term 'Octaves' in Newlands' Law refers to the musical scale, where the eighth note is similar to the first, just as every eighth element in his table showed similar properties.

The 1st period of the periodic table contains only two elements, hydrogen and helium, making it the shortest period. Subsequent periods contain more elements.

Dobereiner's law of triads grouped elements into sets of three based on their chemical properties and atomic masses. Each group is known as a triad.

John Newlands proposed the Law of Octaves in 1864, which stated that when elements are arranged in order of increasing atomic masses, every eighth element has similar properties to the first element, analogous to musical octaves where every eighth note has similar sound.

In the modern periodic table, metals occupy the left and central parts of the table, while non-metals are generally found on the right side.

Lanthanides and actinides are known as inner transition elements and are placed in the f-block at the bottom of the periodic table.

The 6th and 7th periods are considered incomplete because they contain elements that were discovered later or are synthetic, and the 7th period is still being filled.

Atomic mass of an element can vary.

Sulphur is a chalcogen. Chalcogens are the elements in Group 16 of the periodic table, which includes oxygen (O), sulphur (S), selenium (Se), tellurium (Te), and polonium (Po). The term 'chalcogen' means 'ore former' in Greek.

Bromine is the middle element in the halogen triad consisting of chlorine, bromine, and iodine, where its atomic mass is approximately the average of the other two.

Metalloids are found along the diagonal line separating metals on the left and non-metals on the right in the p-block of the periodic table.

Chlorine belongs to Group 17, which is known as the halogen family. These elements are highly reactive non-metals.

Dobereiner classified elements into triads based on their atomic masses, where the middle element had an atomic mass approximately equal to the average of the other two.

Group 1 contains the alkali metals (Lithium, Sodium, Potassium, Rubidium, Cesium, Francium) and Hydrogen, which is a non-metal.

Noble gases are located in Group 18 of the modern periodic table, characterized by having a full valence shell.

Mendeleev's periodic table could not explain the position of isotopes because it was based on atomic masses. Isotopes have different atomic masses but the same atomic number, so they would occupy different positions in Mendeleev's table but should occupy the same position.

In the 5^th period, there are a total of 32 elements.

The horizontal rows of elements in a modern periodic table are called periods and the vertical rows of elements in a periodic table are called groups. There are total 7 periods and 18 groups in modern periodic table.