Atomic Structure First Year Diploma PDF

Atomic Structure First year diploma By. P.S.Gawari  Introduction Atom – Definition – The smallest indivisible particle of an element is called as an atom. Atom is the basic building block of all substances in nature. Electron (e), proton (n) & neutron...

Atomic Structure First year diploma By. P.S.Gawari  Introduction Atom – Definition – The smallest indivisible particle of an element is called as an atom. Atom is the basic building block of all substances in nature. Electron (e), proton (n) & neutron (n) are Fundamental particles of atom Atom consists of 1. Nucleus - It is positively charged central part & consist of Protons & neutrons. Positive charge is due to presence of protons. Neutrons have no charge i.e. Neutral 2. Extranuclear part – It consist of electrons which revolves around the nucleus in the closed concentric circular path called orbit or shell. Electrons are negatively charged. The no of protons in the nucleus is exactly equal to the no of electrons in extra – nuclear part. All positive charge is thus exactly canceled out by all the negative charge present on an atom. Hence, the atom as a whole is electrically neutral. Atomic number (Z)- The atomic number or proton number (symbol Z) of a chemical element is the number of protons found in the nucleus of every atom of that element. Atomic number (Z) = number of protons (p) = no of electrons (e). Atomic mass number (A) - The mass number (represented by the letter A) is defined as the total number of protons and neutrons in an atom. Atomic mass number (A) = number of protons (p) + number of neutrons (n) Examples of Isotopes – 1 H1 1 H2 1 H3 17 Cl 35 17 Cl 37 P = 1 1 1 17 17 n= 0 1 2 18 20 Examples of Isotopes – 18 Ar40 19 K40 20 Ca40  Bohr’s Theory of Atom Postulates or Assumptions – 1. Atom consist of dense positively charged central part called nucleus, which is at rest. 2. Electrons revolved around the nucleus in fixed circular path called orbits or shells. 3. Electrostatic force of attraction between the nucleus and electrons is exactly balanced by the centrifugal force. Hence the electrons does not fall into the nucleus and atom remains stable. 4. Each orbit round the nucleus is associated with a definite amount of energy and the orbital's are called energy levels or main energy shells. They are numbered as 1,2,3,….Starting from the nucleus and are designated by capital letters K,L,M,….  Bohr’s Theory of Atom Postulates or Assumptions – 5. The energy associated with certain energy level, increases with the increase of its distance from the nucleus. 6. While revolving round the nucleus in a fixed orbit, the electron neither loss nor gains the energy and is said to be in a stationary state. 7. However, an excited electron can jump from a lower energy level to higher level by absorbing energy while from higher to lower level by releasing energy in a separate packets called quanta (Photon).  Electronic Configuration 1. Aufbau principle – i. Aufbau principle gives the sequence in which various orbitals are filled with electrons. ii. Definition – In an atom, the orbitals are filled with electrons in order of the increasing energy. iii. The lower energy orbitals are filled first , then higher energy orbitals are filled. The order of filling of the electrons in different orbitals in an atom is: 1S