Railway Science (Chemistry-Periodic Table) (Part-VII)

In the Modern Periodic (given by Henry Moseley) Table, the elements are arranged in the order of their increasing atomic number in seven horizontal rows (periods) and eighteen vertical columns (groups or families). In Mendeleev’s Periodic Table, the elements are arranged in the order of their atomic mass.

Every eighth element has similar properties when the elements are arranged in the increasing order of their atomic masses. Classified the known 56 elements into 11 groups based on their similar physical properties. The Law of Octaves was true only for Elements up to Calcium.

Metalloids (semimetals) are found in groups 13, 14, 15, and 16 of the p-block. Metalloids include Boron (B), Silicon (si), Germanium (Ge), Arsenic (As), Antimony (Sb), Tellurium, (Te), Polonium (Po) and Astatine (At).
Total elements are 118 out of which 91 are metals, 7 are metalloids and 20 are non-metals. Metalloids conduct heat and electricity intermediate between nonmetals and metals and they generally form oxides.

Characteristics of Metal - Good conductor, Forms basic oxides with some being amphoteric, Shiny, Solid at room temperature (except mercury), High boiling point, High melting point; Example - Iron, Copper, Aluminum, Magnesium, Sodium, lead, Zinc.
Characteristics of Non-metal: Bad conductor, Forms acidic oxides with some being neutral, No Shiny, Different states at room temperature, Low boiling point, Low melting point; Example - Carbon, Sulphur, Iodine, Oxygen, Hydrogen.

In Newlands’ Law of Octaves, every eighth element holds the properties same as that of the first element, when elements are arranged in increasing order of their atomic masses. It was relevant upto Calcium only, elements heavier than Calcium did not suit in his table.
He placed two elements in the same slot to fit elements in the table. For example, Cobalt (Co) and Nickel (Ni) are placed in the same slot and in the column of Fluorine, Chlorine and Bromine. But Cobalt and Nickel have properties quite different from Fluorine, Chlorine and Bromine.

Be (Atomic number 4), B (Atomic number 5). Across the period (Left to right) : Atomic number (Increases), Atomic Radius (decreases), Electron affinity (increases), Electronegativity (increases), Ionization energy (increases).
Across the Group (Top to bottom): Atomic number (Increases), Atomic Radius (increases), Electron affinity (decreases), Electronegativity (decreases), ionization energy (decreases).

The number of electrons in the outermost shell of an atom determines its reactivity. As we go down a group the reactivity of non-metals decreases. This is because the number of valence shells increases. The force with which the nucleus holds the electrons decreases.

Halogens (Group 17 elements). It gives salt when reacting with metal and has 7 electrons in their valence shell. Transition elements - Elements that have partially filled ‘d’ orbitals.
Titanium and iron are the most abundant transition elements. Actinoids element (actinide element) - Any of a series of 15 consecutive chemical elements in the periodic table from actinium (89) to lawrencium (103).

The horizontal rows are called periods (7) and the vertical columns are called groups (18). Electronegativity generally increases across a period from left to right and decreases down a group in the periodic table.

They (except for hydrogen) are all soft and shiny with low ionization enthalpies {Elements - Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs), and Francium (Fr)}.
2nd group (Alkaline - earth metal) : They are all reactive metals {Elements - Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), and Radium (Ra)}.