Atoms are the small particles of which every element is made up of. The atom possesses the properties of its element.
Matter comprises of tiny particles called atoms. The chemical properties of an element will be embedded in its atom. The nucleus of an atom comprises of positive charge which consists of positively charged protons and neutrons which are of neutral charge. An atom consists of subatomic particles like protons, neutrons and electrons. The positively charged nucleus is surrounded by negatively charged electrons and the electron number is equal to that of the proton number.
Nucleus of the atom is the dense core of the atom present at the center and surrounded by electron cloud. The nucleons are bound strongly by nuclear force.
The following figure shows the nucleus and elementary particle in the atom.
The total mass of the atom is the collective mass of the nucleons. Electrons possess
Low mass when compared to that of nucleons, so the atomic mass will lie in the nucleus.
Size of an atom size is of the order of 1 Angstrom and the nucleus size is of the order of Fermi meters which are smaller than that of the atom. The nucleus diameter of a hydrogen atom is 1.75 fm and of a uranium atom it is 15 fm.
Atomic number is the total number of protons in an atom and the atomic mass number is the total number of protons and neutrons. It is the number of neutrons relative to the number of protons determines the stability of the nucleus. Heavy nuclides possess stability by undergoing radioactive decay.