Atomic structure converted
- 1. 03-02-2021 1 RADIATION PHYSICS (ATOMIC STRUCTURE) SHILPA THYAGU
- 2. 03-02-2021 2 ATOMIC STRUCTURE • ATOM • STRUCTURE OF AN ATOM • REPRESENTATION OF AN ATOM • DISTRIBUTION OF ORBITAL ELECTRONS • ATOMIC ENERGY LEVELS • CLASSIFICATION OF ATOMS. • NUCLEAR STABILITY • NUCLEAR STABILITY BY N/P RATIO • ATOMIC MASS AND ENERGY UNITS • BINDING ENERGY • NUCLEAR FORCES • PARTICLE RADIATION
- 3. ATOM • All matter is composed of individual entities called elements. each element is distinguishable from the others by the physical and chemical properties of its basic components called ATOM. • ATOM – the name is derived from Greek language ATOMOS means ‘not to be cut’ 03-02-2021 3
- 4. STRUCTURE OF ATOM • Atom consists of positively charged NUCLEUS at the centre and negatively charged Electrons revolving around it. • Radius of an atom -- 10-10 m. • Radius of the nucleus -- 10-15 m. • Nucleus consists of Protons and Neutrons together called Nucleons. • Most of the mass of an Atom is possessed by Nucleus. 03-02-2021 4
- 5. REPRESENTATION OF AN ATOM 03-02-2021 5 EXAMPLE :
- 6. DISTRIBUTION OF ORBITAL ELECTRONS • According to the model proposed by NIELS BOHR in 1913 • The electrons revolve around the nucleus in a specific orbit. • They are prevented from leaving the atom by the centripetal force of attraction between the positively charged nucleus and negatively charged electron. POSTULATES OF BOHR’S THEORY • Electrons can exist in only in those orbits for which the angular momentum of the electrons in an integral multiple of h/2л • No energy is gained or lost while the electron remains in any one of the permissible orbits. 03-02-2021 6
- 7. ATOMIC ENERGY LEVELS • Innermost orbit is called as K-shell (69ev). • Followed by orbital’s called L-shell (500ev), M-shell (1000ev) and N-shell (2500ev). • The maximum no. of electrons in an orbital is given by the formula 2n2. Eg : 1) Hydrogen atom has 1 electron in K-shell 2)Helium atom has 2 electrons in K-shell 3)Oxygen atom has 8 electrons (2 in K-shell, 6 in L-shell) 03-02-2021 7
- 8. NUCLEUS • The nucleus contains two kinds of fundamental particles: protons and neutrons. whereas protons are positively charged and neutrons have no charge. • Number of protons in the nucleus is equal to number of electrons outside the nucleus. • On the basis of different proportions of neutrons and protons in the nuclei, atoms have been classified into isotopes , isotones , isobars, and isomers. 03-02-2021 8
- 9. CLASSIFICATION OF ATOMS • Isotopes Elements having same atomic number (protons) , but different mass numbers (nucleons). Eg: 12C, 13C and 14C There are three isotopes of the element carbon with mass numbers 12, 13 and 14 respectively. The atomic number of all carbon isotopes is 6. • Isobars Elements having same mass number , but different atomic numbers. Eg: 40S , 40Cl , 40Ar , 40K, and 40Ca isobars containing 40 nucleons; however, they contain varying atomic number. 03-02-2021 9
- 10. • Isomers Molecules with the same molecular formula but different chemical structures. That is, isomers contain the same number of atoms of each element, but have different arrangements of their atoms in space. Eg: 131mXe54 is an isomer of 131 Xe54 m stands for meta-stable state Isomers represents identical atoms but they differ in nuclear energy states. • Isotones Nuclides having very same neutron number N , but different proton number Z. Eg: boron-12 Carbon-13 nuclei both contain 7 neutrons 03-02-2021 10
- 11. NUCLEAR STABILTY • The Strong Force is exerted by anything with mass to attract other masses together and works within a very short distance. • Neutrons has no charge, but have the strong force to bring other nucleons together. • Nuclear stability has been analyzed in terms of even and odd number of neutrons and protons • Out of 300 different stable isotopes , more than half have even number of protons and neutrons . This suggests that nuclei gain stability when neutrons and protons are mutually paired. 03-02-2021 11
- 12. NUCLEAR STABILTY • As a general rule, a nucleus will need a neutron/proton ratio of 3:2 in order to stay together. This rule is more precise for larger nuclei of all known isotopes of natural elements (about 1500), only 250 of them are stable • All of these stable isotopes have an atomic number in between 1 and 83. • The mass of a nucleus will be less than the mass of all of the protons and neutrons making it up. The difference is called the mass defect, which is converted into energy if the nucleus is broken up. • The amount of energy that keeps a nucleons together is called the Binding Energy. This amount of energy is higher for nuclei that are stable than it would be for unstable nuclei. (Joules) 03-02-2021 12
- 13. ATOMIC MASS AND ENERGY UNITS • Masses of atoms and atomic particles are conveniently given in terms of Atomic Mass Unit (AMU). • An AMU is defined as ½ of the mass of a 6 12c atom. • 1 AMU = 1.66×10-27 Kg • The mass of an atom expressed in terms of amu is know as atomic mass or atomic weight. • The mass in grams numerically equal to the atomic weight is called gram atomic weight. • According to Avogadro's law , every gram atomic weight of a substance contains the same number of atoms . • Value of Avogadro's number is 6.0221×1023 atoms per gram atomic weight. 03-02-2021 13
- 14. CHARGE AND MASS OF SUBATOMIC PARTICLE • All the atomic masses in units of amu are very nearly equal to the mass number. • The mass of an atom is not exactly equal to the sum of the masses of constituent particles. 03-02-2021 14 Particle Charge of particle Mass of the particle proton 1.602176×10-19 columb 1.00727 amu neutron Electrically neutral 1.00866 amu electron 1.602176×10-19 columb 0.000548 amu
- 15. BINDING ENERGY • An amount of energy equal to the mass defect must be supplied to separate the nucleus into individual nucleons. Therefore, this energy is called binding energy of the nucleus. Binding energy can be calculated by the formula E=mc2 Where, c= speed of light ,m=mass & E = Energy Eg: If a mass of 1 kg is converted into energy, m=1kg speed of light is 3x108 m/s E=1 kg x (3x108 m/s)2 E= 9 x 1016 J Also, Mass of electron at rest in terms of energy equivalent is given by, m=9.1x10-31kg and speed of light is 3x108 m/s E = 9.1x10-31 x (3x108)2 E=8.19x10-14 J E=0.511 MeV 03-02-2021 15
- 16. ATOMIC ENERGY UNIT - JOULE • Basic unit of energy is joule (J) • 1 Joule is the work done when force of 1 Newton is acting through a distance of 1 meter. • Another energy unit in Nuclear physics is electron volt (eV) • 1 eV is defined as the Kinetic energy acquired by an electron in passing through a potential difference of 1V. 1eV=1Vx1.602x10-19 C 1eV = 1.602 x 10-19 J 03-02-2021 16
- 17. NUCLEAR FORCES • A strong attractive force between nucleons in the atomic nucleus that holds the nucleus together is called nuclear force. • There are four different forces in nature, 1. Strong nuclear force 2. Electromagnetic force 3. Weak nuclear force 4. Gravitational force • The nuclear force is the shorter range force that comes into play when the distance between the nucleons become smaller than the nuclear diameter (~10-15) 03-02-2021 17
- 18. PARTICLE RADIATION • The term radiation applies to the emission and propagation of energy through space or material medium. • By particle radiation, we mean energy propagated by travelling corpuscles that have a definite rest mass and within limits have a definite momentum and defined position at any instant. • de-BROGLIE theorized that not only photons sometimes behave like particles (exhibit momentum) but also material particles such as electrons, protons, and atoms have some type of wave motion associated with them (show refraction and other wave like properties). 03-02-2021 18