lec-1(4)(1).pdf

PHYSICS Int oduction  1 Lec Int oduction Bohr Atom Model  A more correct description of the atom states that we can’t know exactly where an electron is at any given time The position o...

PHYSICS Int oduction  1 Lec Int oduction Bohr Atom Model  A more correct description of the atom states that we can’t know exactly where an electron is at any given time The position of an electron is described as a probability   referred to as an electron cloud. Bohr Atom Model  The atomic number Z of an element is equal to the number of protons in the nucleus of that element. The mass number A of an element is equal to the total number of nucleons (protons + neutrons). Isotopes of Elements Isotopes are atoms that have the same number of protons (Z1= Z2), but a different number of neutrons (N).  (A1A2) different atomic masses and physical properties  Example 2: The average atomic mass of Boron is 11.009305 u. What is the mass of the nucleus of one boron atom in kg? given that the atomic number of Boron is 5 (Mass of electron: 0.00055 u) Nucleus mass = atom mass - the mass of 5 electrons Mass of boron nucleus in u is = (11.009305 u) – (5 x 0.00055 u) = 11.00656 u Mass of boron nucleus in kg is = 11.00656 u * 1.6606 x 10-27 kg = 1.83 x 10-26 kg Einstein’s Equivalency Formula the relationship between the mass of a particle and its energy.  What is the energy of 1 u? m= 1u E = (1u) x c2 = (1.66 x 10-27 kg)x(3 x 108 m/s)2 = 1.49 x 10-10 J E = 1.49 x 10-10 J = 931.5 M eV (megaelectron volt)