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

Valency - It is equal to the number of electrons gained, lost or shared by an atom of an element to achieve the nearest noble gas configuration.
Valence - electrons increase from left to right in a period and remain same from top to bottom in a group. In Periodic table the arrangement of elements is in the increasing order of their atomic numbers.

The electron affinity is a measure of the attraction between the incoming electron and the nucleus - the stronger the attraction, the more energy is released. It is denoted by Aₑ and its unit is KJ/mol.
Electron affinity increases upward for the groups and from left to right across periods of a periodic table. The electronic affinity of the Noble gases, Alkali metals, and Alkali earth metals are close to zero. Chlorine has the highest electron affinity among the elements.

Group number. Shell number - The total number of shells indicates the period number. Atomic mass (atomic weight) of an element is defined as the relative mass of the atom of the element as compared to the mass of an atom of C−12 isotope. Atomic number is equal to the number of protons in the nucleus of an atom or the number of electrons in an electrically neutral atom.

Atomic radius - The total distance from an atom's nucleus to the outermost orbital of electrons. It increases from top to bottom in a group. Electron affinity - The energy change that results from adding an electron to a gaseous atom.
Electronegativity - The tendency of an atom or a functional group to attract electrons toward itself. Ionisation energy - The tendency of a neutral atom to resist the loss of electrons.

Bridge elements are those elements which show the diagonal relationship with the element of the neighboring period. Examples - Lithium (Li) and Magnesium (Mg), Beryllium (Be) and Aluminium (Al).
The alkaline earth metals are six chemical elements in group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).
Transition elements are elements found on the periodic table in Groups 3-12. Example - Tungsten (W), platinum (Pt), gold (Au), and silver (Ag).

{Symbol: Ge, Atomic number (Z): 32}. Uses: Semiconductor (Most widely), transistors, integrated circuits, alloying agents. Silicon (Si, Z-14): Widely used as a semiconductor and the second most abundant element on Earth's crust.
Oxygen (O, Z-8):Makes up nearly 21% of the Earth's atmosphere. It is a colorless and odorless gas. Chlorine (Cl, Z-17): Belongs to the group of Halogens. It is a yellow-green gas and used as a disinfectant and to treat drinking water.

Actinide series includes 15 radioactive elements with atomic numbers 89 (Actinium, Ac) to 103 (Lawrencium, Lr). Actinides and lanthanides are elements with unfilled ‘f’ orbitals and are collectively labeled as the Inner transition elements (ITEs). Lanthanide series is made up of 15 elements with atomic numbers 57 (Lanthanum, La) to 71 (Lutetium, Lu).
p-block elements are elements in which the last electron occupies p-orbitals and are found in groups 13, 14, 15, 16, and 17 (except helium).
S-block elements are those in which last electron enters the outermost s-orbital. It contains alkali and alkaline earth metals of group 1 and 2.

Metal: These elements have a tendency to lose one or more electrons to attain a stable electronic configuration. Placed towards the left side on the periodic table. Examples: Sodium (Na), Calcium (Ca), Potassium (K), etc.
Non - Metals: These elements have a tendency to gain one or more electrons to attain a stable electronic configuration. Placed towards the right side. Examples: Oxygen (O), Nitrogen (N), Chlorine (Cl), etc.

A diagonal relationship is said to exist between certain pairs of diagonally adjacent elements in the second and third periods of the periodic table. Many of the chemical properties of an element are related to the size of the atom. These pairs are lithium (Li) and magnesium (Mg), beryllium (Be) and aluminum (Al), boron (B) and silicon (Si) as they exhibit similar properties. For example - boron and silicon are both semiconductors, forming halides that are hydrolyzed in water and have acidic oxides.

18th Group element (Noble Gases): Noble gasses in the periodic table are Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), Radon (Rn). Its Outermost shell has 8 electrons.
The noble gasses except helium (1s² ) have completely filled ns²np⁶ electronic configuration in their valence shell. Other groups and the number of electrons their outermost shell contains : 15th Group (Pnictogens) - 5 electrons. 16th Group (Chalcogens) - 6 electrons. 17th Group (Halogens) - 7 electrons.