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

Vertical columns in the periodic table starting from top to bottom. Characteristics - All the elements show the same valence electrons in a group, Metallic character increases down the group, Same chemical properties, physical properties Varies. Periods: The horizontal rows in the periodic table. Characteristics - Electrons of the elements occupy the same shell, chemical properties of the elements change, Atomic size of the elements in a period decreases from left to right.

Electron Affinity - the energy change when a gaseous atom gains an electron to form a negative ion (anion). It generally increases across a period (from left to right) on the periodic table due to increasing effective nuclear charge, leading to stronger attraction for electrons, while it decreases down a group (top to bottom) due to increased atomic size and shielding effects. Correct order: Cl (Chlorine)> F (Fluorine)> Br (Bromine)> I (Iodine).

Atomic number 16, has 2,8,6 configuration and it has 6 valence electrons in the third orbit. The third period contains eight elements: sodium (Na, 11), magnesium (Mg, 12), aluminum (Al, 13) silicon (Si, 14), phosphorus (P, 15), Sulfur (S, 16), chlorine (Cl, 17), and argon (Ar, 18).

Semiconductor: A class of crystalline solids intermediate in electrical conductivity between a conductor and an insulator. The elemental semiconductors are those composed of single species of atoms, such as Silicon (Si), and Tin (Sn) in column IV and Selenium (Se) and Tellurium (Te) in column VI of the periodic table. These are used in electronic devices, including diodes, transistors, and integrated circuits.

Sodium (Symbol Na, Atomic number 11). Alkali metals are characterised by their softness, low  density, and high reactivity. Manganese - Transition metal which belongs to a group 7. Aluminum - Post-transition metal which belongs to Group 13. Magnesium is an alkaline earth metal which belongs to Group 2.

Elements from groups 3 to 12 are called d-block elements or transition elements. These are those elements whose two outermost shells are incomplete. These elements have partially filled d-subshells in ground state.

The element which has two shells both of which are completely filled with electrons is Neon with electronic configuration (2, 8). Helium (He) only has 2 electrons and therefore it has a configuration of 1s² . Argon (Ar) electron configuration will be 1s² 2s² 2p6 3s² 3p⁶ . Electron configuration of Krypton (Kr) : 1s² 2s² 2p6 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ .

Lanthanides contain elements from the atomic numbers 57 to 71. It is also called Rare Earth Metals. Actinides are 15 elements that start with the atomic number 89 and go up to the atomic number 103. Lanthanides and Actinides are radioactive in nature. They consist of 30 elements in total.

Arsenic (As) and Bismuth (Bi) are in the same group.

In the Modern Periodic Table, elements present in the same period will have the same number of shells. Valence electrons are electrons in the outermost shell of an atom. The combining capacity of an element is known as its valency.