Chronon

  In our previous blogs, we talked about atomic number and mass number. On the basis of atomic and mass number, atom is further divided into two species.  Today we are going to discuss these species of the atom. First one is;   Isotopes In nature, such atoms of some elements have been identified, which have the same atomic number but different mass numbers. For example, in the case of hydrogen atom, it has three atomic species, namely protium ( 1 1 H), deuterium ( 2 1 H or D) and tritium ( 3 1 H or T). The atomic number of each one is 1, but the mass number is 1, 2 and 3, respectively. Other such examples are (i) carbon   12 and carbon 14, having mass number 12 and 14 respectively, (ii) chlorine 35 and chlorine 37, having mass 35 and 37 respectively. These species are called Isotopes. Isotopes are defined as the atoms of the same element, having the same atomic number but different mass numbers. Therefore, we can say that there are three isotopes of hydrogen a...

In our previous blog we have come across charged particles, atomic structures, electrons distributions and valency of the atom. Today we are going to talk about some other terms of atoms we use in our studies. The first one is; Atomic Number The atomic number is defined as the total number of protons present in the nucleus of an atom. It is denoted by ‘Z’. We know that all the   protons are present only inside the nucleus of an atom. All atoms of an element have the same atomic number, Z. In fact, elements are defined by the number of protons they possess. For hydrogen, Z = 1, because in hydrogen atom, only one proton is present in the nucleus. Similarly, for carbon, Z = 6.   Mass Number In 1932, J. Chadwick discovered another subatomic particle which had no charge and a mass nearly equal to that of a proton. It was eventually named as neutron. Neutrons are present in the nucleus of all atoms, except hydrogen. In general, a neutron is represented as ‘n’. After st...

  In our previous blog we have learnt how the electrons in an atom are arranged in different shells/orbits. Today we are going to talk about the valency or combining capacity of an atom. The electrons present in the outermost shell of an atom are known as the valence electrons. From the Bohr-Bury scheme, we also know that the outermost shell of an atom can accommodate a maximum number of 8 electrons. It was observed that the atoms of elements, having a completely filled outermost shell show little chemical activity. In other words, atoms having completely filled outermost shell have no combining capacity or their valency is zero. These elements are known as inert elements. Like the helium atom has two electrons in its outermost shell and all other elements have atoms with eight electrons in the outermost shell. The combining capacity of the atoms to other elements, or their tendency to react and form molecules with atoms of the same or different elements are known as valency. T...

In our previous blogs we talked about different structures of atom. When structure of atom was stablished as we discussed in our last blog, scientists studied about arrangements of atoms in the orbitals and atomic valency. Today we will discuss about distribution of electrons in different orbitals. Irving Langmuir was the first to propose the distribution of electrons in different orbitals. In 1919 he published an article "The Arrangement of Electrons in Atoms and Molecules" in which he explained the arrangements. In 1923 Niels Bohr incorporated Langmuir’s model that the periodicity in the properties of the elements might be explained by the electronic structure of the atom.  His proposals were based on the current Bohr model of the atom. The following rules are suggested for writing the number of electrons in different energy levels or shells: The maximum number of electrons present in a shell is given by the formula 2n 2 , where ‘n’ is the orbit number or energy level ind...

In our previous blog, we talked about Rutherford's model of atom. According to his model, protons are concentrated in the center in a small volume of the atom and electrons are revolving around them. The Irish physicist, Joseph Larmor, published in 1895, the first analysis concerning radiation by an accelerated charge based upon the derivation by Hendrik Lorentz of the force experienced by a particle due its charge field being dragged through the ether. According to this analysis, the revolution of the electron in a circular orbit is not expected to be stable. Any particle in a circular orbit would undergo acceleration. During acceleration, charged particles would radiate energy. Thus, the revolving electron would lose energy and finally fall into the nucleus. If this were so, the atom should be highly unstable and hence matter would not exist in the form that we know. In order to overcome the objections raised against Rutherford’s model of the atom, in 1915 Neil Bohr modifie...

In our previous blog we talked about Thomson's Model of Atom. From the blog we also know that, his model was the first atomic model ever proposed. But we all know that this atomic model was unable to explain lots of results of experiments carried out by other scientists. Today we are going to talk about one of those experiments and its results. In 1911, Ernest Rutherford overturned Thomson's model with his well-known "Gold Foil Experiment". In this experiment, he made fall fast moving alpha (α)-particles on a thin gold foil. He selected a gold foil because he wanted as thin a layer as possible in this experiment. This gold foil was about 1000 atoms thick. α-particles are doubly-charged helium ions. Since they have a mass of 4 u, the fast-moving α-particles have a considerable amount of energy. It was expected that α-particles would be deflected by the sub-atomic particles in the gold atoms. Since the α-particles were much heavier than the protons, he did not expect t...

  We have talked about Dalton's Atomic theory in our previous blog. According to his theory atom was invisible and indestructible. In our last blog, we talked about charged particles of matter, also known as fundamental particles. Discovery of these fundamental particles, electrons and protons, led to the failure of aspects of Dalton's atomic theory. After this failure, it was considered necessary to know that how the electrons and protons are arranged in atom.  To explain this, many scientists proposed various atomic models. J.J. Thomson was the first to propose a model for the structure of an atom. In the March of 1904, Thomson published his model of the atom in "Philosophical Magazine" the leading British science journal of the day. He proposed that the model of an atom is similar to Christmas pudding. The electrons are in a sphere of positive charge like dry fruits in a spherical Christmas pudding. We can also think of an watermelon. While the electrons are studde...

Have you ever tried to attract small pieces of paper with comb after combing dry hair or attract an inflated balloon with glass rod after rubbing rod with silk? What do you think, why they attract?  In our previous blog we talked about molecular mass and mole concepts. Today we are going to talk about charged particles in matter and some of their interesting behavior .  It was known by 1900 that atom was not a simple, individual particle but contained at least one subatomic particle - the electron identified by J.J. Thomson in 1897. Even before the electron was identified, E. Goldstein in 1886 discovered the presence of new radiations in a gas discharge and called them canal rays. Later we found that the canal rays were positively charged radiations which ultimately led to the discovery of another subatomic particle. This subatomic particle also had a charge, equal in magnitude but opposite in behavior to that of the electron. Its mass was approximately 2000 times as that of e...