Railway Science (Chemistry-Structure of Atom)

It states that electrons fill lower-energy atomic orbitals before filling higher-energy ones, By following this rule, we can predict the electron configurations for atoms or ions. Pauli exclusion principle- In a single atom, no two electrons will have an identical set or the same quantum numbers. Hund's rule - Every orbital in a sublevel is singly occupied before any orbital is doubly occupied. The Wiswesser rule gives a simple method to determine the energetic sequence of the atomic subshells (n, l). n is the principal quantum number and l is the azimuthal quantum number.

His experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. Ernest Rutherford (Father of Nuclear Physics): He discovered the nucleus of the atom in 1911. John Dalton discovered the atomic theory of matter.

It is the amount of a substance that reacts with or replaces one mole of hydrogen ions or one mole of electrons in a chemical reaction. Valency - It is the combining capacity of an element, representing the number of electrons it can gain, lose, or share when forming chemical bonds. It always remains the same down the group but it increases then decreases across the period.

Nucleon is considered as a subatomic particle of the atomic nucleus. Each atomic nucleus can have one or more Nucleons.

The electrons revolve around the nucleus in a specific circular path known as orbit or called a shell. The electrons revolve only in those orbits which have a fixed value of energy. For example, the maximum number of electrons that can be filled in the - First shell (K - Shell) = 2 electrons, Second shell (L - Shell) = 8 electrons, and Third shell (M - Shell) = 18 electrons, Fourth shell (N - shell) = 32 electrons.

Rutherford’s Alpha Scattering Experiment - Rutherford passes very high streams of alpha-particles from a radioactive source i.e. alpha-particle emitter, at a thin sheet of 100 nm thickness of gold. Protons (Rutherford) have a positive charge while electrons (Thomson) have a negative charge. Neutrons (James Chadwik) don't have a charge.

It is a Noble gas in the Group 18 of the periodic table. Atomic number - 54. Atomic Mass - 131.29. Subatomic particle - A particle which is smaller than an atom in size. Three primary subatomic particles: Proton- Discovered by Ernest Rutherford, Electron - Discovered by J. J. Thomson, Neutron - discovered by James Chadwick.

Atom is named after a greek word “atomos” which means indivisible. J.J. Thomson - Discovered electrons and proposed a plum pudding model for an atom. Ernest Rutherford - Discovered the atomic nucleus. John Dalton - Proposed the atomic theory of matter and also researched on color blindness.

The number of particles (atoms, molecules or ions) present in 1 mole of any substance is fixed, with a value of 6.022 × 10²³ . This is an experimentally obtained value. This number is called the Avogadro Constant or Avogadro Number (represented by Nₐ or Nₒ), named in honor of the Italian scientist, Amedeo Avogadro.