Fundamental properties of atom
Size of the atom and mass of the atom are fundamental properties of atom. The size of the atom was previously expressed in terms of its radius in Angstroms unit, A0, (1A0 = 10−10 cm). Now a days, the size of the atom is expressed in pico-meter (1 pm = 10−12 cm). The radii of H, Cl and U are 37.1, 100 and 156 pico meter respectively.
Almost all mass of atom is concentrated in its nucleus. The atomic mass (earlier called atomic weight) is of the order of 10−26 kg. Previously, atomic mass was expressed in atomic mass units (amu). Today, atomic mass is expressed as ’u’ and 1 u = 1.66 x 10−27 kg.
From all the above facts expressed above, it is clear that the atoms cannot be seen, but their presence is only felt due to the effects that they display. These effects are in the form of chemical reactions – combinations of two or more elements at atomic level or their splitting, creating different elements and in the course of these reactions energy levels undergo changes. Splitting of an atom also follows these rules.
Matter cannot be created or destroyed. It only changes forms and in doing so immense energy is released or absorbed (from elsewhere – elements in contact).