Railway Science (Chemistry-Structure of Atom)

Sulphur (S) - 8 atoms. It is a brittle solid, a poor electrical conductor, and is used in fertilizers, batteries, and gunpowder. Phosphorus (P) - 4 atoms. P is toxic and used in fertilizer formation. Neon (Ne) - 2 atoms. Ne is the second-lightest noble gas and is used in lamps, and high-voltage indicators. Argon (Ar) - 1 atom. Ar is an odorless, colorless inert gas.

The atomic number of an element is determined by the number of protons in it, and it is used to differentiate one element from another. The mass number of an element is determined by the number of protons and neutrons combined. The atomic mass unit (AMU or amu) of an element is a measure of its atomic mass. AMU is defined as one-twelfth the mass of an atom of carbon-12 (12C).

The attractive positive charge of nuclear protons acting on valence electrons. It is always less than the total number of protons present in a nucleus due to the shielding effect. The periodic table tendency - increase across a period, increase down a group. The effective nuclear charge increases in period from left to right as the table unfolds. Effective nuclear charge is dependent on the number of electrons present in an atom.

any substance that has mass and occupies space by having volume. Everything in this universe is made up of Matter. 3 states of matter – solid, liquid and gas. These states of matter arise due to the variation in the characteristics of the particles of matter. Solid - definite shape, distinct boundaries and fixed volumes, that is, have negligible compressibility. Liquids - fluids that have no fixed shape but have a fixed volume. They take up the shape of the container in which they are kept. Gases - No fixed shape and volume, highly compressible in nature.

A charged atom or molecule is known as an ion. There are two types of ions: positive ions (cation) and negative ions (anion). Some examples of cations : Calcium (Ca2⁺), Potassium (K⁺ ), hydrogen (H⁺ ). Examples of anions : Iodide (I⁻ ), chlorine (Cl⁻ ), hydroxide (OH⁻ ). Molecule: It is made up of two or more atoms.

protium (no neutrons), deuterium (one neutron) (also known as heavy hydrogen) and tritium (two neutrons). It is a colourless, odourless, tasteless, flammable gas. It exists as a diatomic molecule, H₂ . Isobars - Elements having the same mass number but different atomic numbers. Some common Isobars: Argon ₁₈Ar⁴⁰ and Calcium ₂₀Ca⁴⁰ Isotones - Atoms of different elements that have the same number of neutrons. Example: Boron-12 and Carbon-13 and Nitrogen-14 (both have 7 neutrons).

They are Uranium 235 and Plutonium 239. Nuclear energy is created when Uranium atoms are split in a process called Fission (releases a tremendous amount of energy in the form of heat).

The Atomic Mass of an element is the average mass of the atoms of an element measured in atomic mass unit (amu, also known as dalton, Da). The Formula Mass of a substance is defined as the sum of the atomic masses of constituent atoms in an ionic compound. One Mole is defined as the amount of substance containing as many elementary entities (atoms, molecules, ions, electrons, radicals, etc.) as there are atoms in 12 grams of Carbon - 12 (Nₐ = 6.023 × 10²³ = Avogadro's number).

Nitrogen (N, Atomic number: 7) has 5 electrons in its valence shell. It can therefore accept 3 electrons to complete its octet. Valency of hydrogen is 1. Ammonia (NH₃) is an inorganic compound composed of a single nitrogen atom covalently bonded to three hydrogen atoms and mainly used in agriculture as fertilizer. It is also used as a refrigerant gas and in the manufacture of plastics, explosives, textiles, pesticides, dyes and other chemicals.

The atomic number (Z) of an element is equal to the number of protons in the nucleus of an atom. The difference between the mass number (A) and the atomic number (Z) gives the number of neutrons (N) in the nucleus: N = (A − Z). Avogadro's number (Nₐ) represents the number of atoms or molecules that are in a mole of a substance. Nₐ = 6.02214 × 10²³ .