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

The reactivity series is a list of metals arranged in the order of their decreasing reactivities. The metals at the top of the reactivity series are powerful reducing agents. The least reactive metals are Platinum, Gold, Palladium, Osmium, etc.

In Mendeleev's periodic table elements were arranged on the basis of the fundamental property, atomic mass, and chemical properties. Father of the periodic table - Dmitri Mendeleev. Modern periodic table discovered by - Henry Mosely.

(Carbon family) - Carbon (C), Silicon (Si), Germanium (Ge), Tin (Sn), and lead (Pb). All these elements have four electrons in their outermost energy level. Silicon and Germanium are metalloids, Lead and Tin are metals so carbon is the only nonmetal in this group.
A series of six elements - Boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb) and tellurium (Te) called metalloids separate the metals from the nonmetals in the periodic table.

These are odorless, colorless, monatomic gases with very low chemical reactivity. Their outermost shell contains 8 electrons {except helium (2 electrons)}, so they are stable elements.

Electronegativity - The tendency of an atom or a functional group to attract electrons toward itself. If two atoms are bonded together and one atom is more electronegative than another bonded atom, then the electron density of the bond would shift slightly towards the more electronegative atom.
These types of bonds are called polar bonds or polar covalent bonds. Electronegativity increases by moving left to right across a period and electronegativity decreases by moving down the group. Described by - Linus Pauling. Most electronegative element - Fluorine.

Elements belonging to the same group have similar properties because they have similar electronic configurations of the outermost shell.
Example - pairs of Nitrogen (N) and Phosphorous (P), lithium (Li) and magnesium (Mg), Beryllium (Be) and Aluminium (Al), Boron (B) and Silicon (Si) etc.

Dobereiner arranged the elements in increasing order of atomic masses. The atomic mass of the middle element was approximately equal to the arithmetic mean (average) of the atomic masses of the other two elements of that triad. Example - Lithium (Li), sodium (Na) and potassium (K) with atomic masses 7, 23, and 39 constitute a Dobereiner's triad.

Because the effective nuclear charge acting on the valence shell electrons increases across a period and decreases down the group. The periodic table was published in 1872. Mendeleev arranged elements based on their atomic mass and physical properties.

Diatomic elements - Hydrogen (H₂), Nitrogen (N₂) and Oxygen (O₂). Triatomic molecule - Molecules composed of three atoms, of either the same or different chemical elements. Example - Ozone (O₃) and Water(H₂O). Monoatomic molecule - Molecules of some elements consist of only one atom.
Example - All noble gases - helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). Tetra atomic molecule - The molecules that contain four atoms either same or different. Example - Phosphorus (P₄).

John Newlands - introduced the concept of octaves (where properties repeat for every eighth element).