Atomic structure and interatomic bonding. Рroblem solutions

ATOMIC STRUCTURE AND INTERATOMIC BONDING

PROBLEM SOLUTIONS

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 12C), 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 = 







 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