Dental Radiography Principles and Techniques (2016 , Saunders)

Dental Radiography Principles and Techniques (2016 , Saunders) The identity of an atom is determined by the composition of its nucleus and the arrangement of its orbiting electrons. At present, 105 different atoms have been identified. - ANSWER Protons carry positive electrical charges,whereas neutrons carry no electrical charge. The nucleus of an atom occupies very little space; in fact, most of the atom is empty space. For example, if an atom were imagined to be the size of a football stadium, the nucleus would be the size of a football. Atoms differ from one another on the basis of their nuclear composition. The number of protons and neutrons in the nucleus of an atom determines its mass number or atomic weight. The number of protons inside the nucleus equals the number of electrons outside the nucleus and determines the atomic number of the atom. - ANSWER Electrons are tiny, negatively charged particles that have very little mass; an electron weighs approximately 1/1800 as much as a proton or neutron. The arrangement of the electrons and neutrons in an atom resembles that of a miniature solar system. Just as the planets revolve around the sun, electrons travel around the nucleus in well-defined paths known as orbits or shells. - ANSWER An atom contains a maximum of seven shells, each located at a specific distance from the nucleus and representing different energy levels. The shells are designated with the letters K, L, M, N, O, P, and Q; the K shell is located closest to the nucleus and has the highest energy level Electrons are maintained in their orbits by the electro static force, or attraction, between the positive nucleus and the negative electrons. This is known as the binding energy, or binding force, of an electron. - ANSWER The binding energy is determined by the distance between the nucleus and the orbiting electron and is different for each shell. The strongest binding energy is found closest to the nucleus in the K shell, whereas electrons located in the outer shells have a weak binding energy. The binding energies of orbital electrons are measured in electron volts (eV) or kilo electron volts (keV