Structure of Atoms – Structure of An Atom
* An Atomic Number is the number of protons in an atom.
* The arrangement of electrons in various energy levels of an atom known as electronic configuration
* The maximum number of electrons in any energy level of the atom is given by 2n2.
* The outcome shell of an atom cannot accommodate more than eight electrons.
* Combining capacity of the atoms to form molecules either with the same or different elements is known as valency.
* Neutron is a neutral particle present in the nucleus.
* The total number of protons and neutrons present in one atom of an element is referred as atomic mass.
* Isotopes are atoms with same atomic number but different mass number.
* Isotopes of certain elements are used in a nuclear reactor, and in the treatment of cancer and goitre.
* Atoms of different elements with different atomic number that have the same mass number are called Isobars.
Isotopes and Isobars
* Mass number is the sum of the number of protons and the number of neutrons.
* The atomic number is the number of protons.
* Isotopes have same number of protons but different number of neutrons.
* As the Isotopes have the same number of electrons and protons, they have similar chemical properties.
* Isobars are the atoms of different elements having different atomic numbers but same mass numbers.
* Isobars have different chemical properties because they have different atomic numbers but same mass numbers.
Nuclear Binding Energy and Nuclear Stability
* Mass defect (Δm) is the different between the theoretically expected mass of the nucleus and the actual mass of the nucleus.
* The energy equivalent to the mass defect is called the binding energy (Eb). This energy is released when the constituents of a nucleus are brought together. This same energy is required to break a nucleus into its constituent nucleons.
* The ratio of the binding energy to mass number of nucleus is called as the binding energy per nucleon or average binding energy (Ebn).
* Nuclear force is a strong attractive force between the nucleons in the nucleus, which binds the nucleons together in the tiny nuclear volume in spite of the coulomb repulsive forces that exist between the positively charged protons.
* Nuclear force is short ranged but is the strongest force in nature.
* Nuclear forces are independent of charge.
* A nucleon will be under the influence of some of its neighbours, which come within the range of the nuclear force.
* The property that a given nucleon is influenced only by nucleons close to it is referred to as the saturation property of the nuclear force.
Alpha, Beta, and Gamma Decay
* During a radioactive decay process, the original nucleus is referred as parent nucleus and the residual or resultant nucleus is referred as daughter nucleus.
* In nature, a radioactive nucleus can decay by three modes namely alpha decay, beta decay and gamma decay.
* In alpha decay, a radioactive nucleus emits a helium nucleus, which is referred to as an alpha particle.
* The difference between the rest mass energy of the final products is called the Q value of the reaction.
* In beta-minus decay, a neutron transforms into a proton within the nucleus.
* Along with this transformation, an electron and an antineutrino are also emitted.
* In beta- plus decay, the radioactive nucleus emits a high- energy photon.
Nuclear Energy
* When tightly bound nuclei transform into relatively less tightly bound nuclei, nuclear energy is released.
* The nuclear energy obtained for the same mass is enormous compared to that of the conventional sources of energy.
* When neutrons are bombarded onto various elements, new radioactive elements can be produced.
* A nuclear fission process generates an enormous amount of heat energy.
* Nuclear fission products are highly rich in neutrons, and are unstable and radioactive. They emit beta particles in succession until they reach a stable end-product.
Nuclear Fission
* When the nucleus of a heavy element is bombarded with neutrons splits into two or more smaller nuclei and releases energy. Such a process is called “nuclear fission”.
* The amount of energy released in each fission reaction is 200 MeV.
* A nuclear chain reaction is a process in which a series of self-sustained nuclear fissions take place as the neutrons produced in each fission cause additional fissions.
* Reproduction factor k is defined as the ration of the number of neutrons present in a particular generation to the number of neutrons present in the preceding generation.
* The nuclear waste produced in a nuclear reactor is extremely hazardous and must be handled carefully.
Nuclear Fusion
* The nuclear reaction in which lighter nuclei combine to form a heavier nucleus with the release of an enormous amount of energy is called “nuclear fusion”.
* The energy released per nucleon is much higher in a nuclear fusion reaction than in a nuclear fission reaction.
* Nuclear fusion reactions can take place only at very high temperatures.
* Nuclear fusion reactions that take place at very high temperatures are called “thermo-nuclear reactions”.