Exam (elaborations) TEST BANK FOR Engineering Materials Science By Milton Ohring (Solution Manual)

2.1 (a) When two or more atoms of an element have different atomic masses, each is termed an isotope. (b) The atomic weights of the elements ordinarily are not integers because: (1) the atomic masses of the atoms generally are not integers (except for 12 C), and (2) the atomic weight is taken as the weighted average of the atomic masses of an atom's naturally occurring isotopes. 2.2 Atomic mass is the mass of an individual atom, whereas atomic weight is the average (weighted) of the atomic masses of an atom's naturally occurring isotopes. 2.3 (a) In order to determine the number of grams in one amu of material, appropriate manipulation of the amu/atom, g/mol, and atom/mol relationships is all that is necessary, as #g/amu = èç æ ø÷ ö 1 mol 6.023 x 1023 atoms ( 1 g/mol ) 1 amu/atom = 1.66 x 10-24 g/amu (b) Since there are 453.6 g/lbm, 1 lb-mol = (453.6 g/lbm)(6.023 x 1023 atoms/g-mol) = 2.73 x 1026 atoms/lb-mol 2.4 (a) Two important quantum-mechanical concepts associated with the Bohr model of the atom are that electrons are particles moving in discrete orbitals, and electron energy is quantized into shells. (b) Two important refinements resulting from the wave-mechanical atomic model are that electron position is described in terms of a probability distribution, and electron energy is quantized into both shells and subshells--each electron is characterized by four quantum numbers.