The atomic structure of the matter
The atom is the fundamental building unit of the matter , and it is the smallest individual unit of the matter which can share in the chemical reactions , Boyle , Thomas , Rutherford and Bohr are from the scientists who contributed the discovery of the atom construction .
The atomic radius of an atom is measured by unit called Angestrom , And one Angestrom equals a part of ten thousands million parts of one metre , The radius of hydrogen atom equals 0.3 Angestrom , and this indicates how much the atom is small .
The atomic construction
The atom consists of the nucleus and the electrons , and it is electrically neutral in its ordinary state , The nucleus is the central core of the atom , where the mass of the atom is concentrated in it .
The nucleus is positively charged as it contains the protons ( positively charged particles ) and the neutrons ( electrically neutral particles ) , The atomic number and the mass number to express the atom of any element .
The atomic number is the number of the protons in the nucleus of an atom , and it is written below the symbol from the left , The mass number is the sum of the numbers of protons and neutrons in the nucleus of an atom , and it is written above the symbol from the left side .
The electrons are negatively charged particles , they revolve around the nucleus with very high speed , The electrons has a negligible mass relative to that of the protons or the neutrons , so the mass of the atom is concentrated in the nucleus .
The number of the negative electrons which revolve around the nucleus is equal to the number of the positive protons in the nucleus , so the atom is electrically neutral in its ordinary state .