CONCEPT OF ATOMIC PARTICLES By-N.K.D. Sir Please -Rate review and share this lesson
Proton (iH1, Ht,P) It was discovered by Rutherford. It is a positively charged particle. The magnitude of charge on proton is the same as that on an electron. Proton, like electron, is a fundamental particle and is universal component of matter. MORE ABOUT PROTON o charge on proton = 1.6 10-19 coulomb = 4.8 10-10 e.s.u. Mass of proton = mass of hydrogen atom = 1837 times the mass of electron 1.00747 a.m.u. = 1.6726 10-24 gram = 1.6726 10-27 kg.
4 Volume of a pnis roughly close to 1.5 x 1038 cm3. Mass of one mole of protons is about 1.007 gm. Proton is protium nucleus Proton is ionized hydrogen atom (H) Removal of solitary electron from hydrogen atom gives proton. Hydrogen atom minus electron is proton
Neutron (on , N) It is a chargeless particle i.e., it is neutral. It was discovered by James Chadwick. The reason of its late discovery is its charglessness When beryllium or boron is bombarded with o-particles, highly penetrating radiations are obtained These radiations are not deflected from their path by strong magnetic or electric field. These radiations are composed of chargeless particles, known as neutrons. IMPORTANT POINTS ABOUT NEUTRON Mass of neutron1.00899 a.m.u - 1.6749 x 1027 kg 3 Actual mass of neutron is slightly greater than that of proton. Density of neutron is of the order 10" kg/cc 12 3 Out of the three types of fundamental particles, neutron is the most unstable. It decays as follows: 0 Neutron Proton Electron Antineutrino
Neutrino and antineutrino These are the particles of gold was bombarded with -particles emitted from radium, it was observed by Rutherford that (i) A large number of a-particles penetrated through the metal foil straightway. ii) Some were deflected from their path through large angles. ii) Very few a -particles returned back after striking the metal foil. The following conclusions were drawn from these experiments. (a) A major portion of atom is empty space, because most of the E-particles pass straight through the atom. (b) The atom has a very small, rigid, positively charged body called the nucleus. -particles are repelled from the metal foil due to this +vely charged part. (c) The whole mass of the atom is concentrated in the nucleus. So, it is very heavy and ridig. Due to its rigidity and +ve charge, the heavy a-particles are thrown back after striking the metal foi
Propertiees Electron e or e 1/1836 Proton Neutron Symbol Approximate relative mass Approximate relative charge Mass in kg Mass in amu Actual charge (coulomb) Actual charge (e.s.u.) -1 No charge 1.675 10-27 1.008 9.109x10-31 5.485 10 4 1.602x1019 4.8x101o 1.673x10-27 1.007 1.602x1019 4.8 10-10
IMPORTANT POINTS ABOUT THE NUCLEUS Size of nucleus is measured in Fermi (1 fermi 1013 cm) o Size of the nucleus is of the order of 10 to 101 cm The nuclear size depends upon mass number (A). It is proportional to the cube root of mass number. Thus nuclear size (R) is R Ro A1 where Ro is a constant (1.4 x 1015 cm), and A is the mass number. Atomic size is of the order 103 cm. Thus atomi nucleus. Nucleus contains protons and neutrons. These nuclear particles are collectively known as 1/3 about 10 times bigger than the Nucleons
Mass Number (A) and Atomic Number (Z) The sum of protons and neutrons present in the nucleus is called mass number. It is always a whole number. The mass number is denoted by the symbol 'A' . Since, electrons have negligible mass, therefore, the entire mass of atom is due to nucleons (neutrons and protons). Mass number (A) Number of protons +Number of neutrons The concept of atomic number was given by Moseley. He observed that when a beam of high speed electrons is bombarded on a metal, X-rays are emitted. The emitted X-rays have wavelength related to the number of protons present in the nucleus of metal atom. This number of protons present in the nucleus of the atom is called atomic number denoted by "Z". The square root of the frequency of emitted X-rays is proportional to the atomic number of metal which is bombarded with the stream of electrons. o Moseley's relation is alz-b), where v frequency of emitted X-rays, Z- atomic number of the metal, 'a' and 'b' are constants.
Atomic number of an element is also equal to the number of electrons present in the outer shells around the nucleus since atom as a whole is electrically neutral. Atomic number = Number of protons in the Nucleus Number of electrons in neutral atom Atomic number is fundamental property of an element. Two different elements can never have identical atomic numbers. The atom of an element 'X' having Mass number 'A' and atomic number 'Z' is represented by symbol, zXA Number of neutrons A-Z.
Niranjay Kumar Dwivedi
(N.K.D.Sir) is a Complete Chemistry faculty for IIT~JEE, and NEET examination. with more then 8 year of Teaching experience