Answers from problem # 20

(a)
Given;
Electronic configuration of 1s² 2s² 2p6 3s² 3p5.
Required;
The atomic number of an atom,Z.
Solution.
The reader must remember that, the atomic number,Z is equivalent to the number of protons in an atom such that for a neutral atom the proton number(°P) is equal to the number of electrons(°e).
Provided the electron number(°e)=2+2+6+2+5.
°e=17.
Since; °e≡°P≡Z=17.
.: The atomic number,Z=17.

(b)
Given;
                37           35
Isotopes    X  and     X.
Relative atomic mass of X, R.A.M=35.5.
Required;
The percentage of
37           35
    X and     X in X.
Solution.
%composition of X=100%.
Let:  37                 35
       %  X=a and %  X=b
So that:  a + b = 100%...(i)
Yet the R.A.M= sum of the products of the % composition of each isotope to its atomic mass divided by 100.
R.A.M= (a×37) + (b×35)
                        100
⇒37a+35b=3550...........(ii)
Solving equations (i)&(ii) simultaneously gives
a=25 and b=75.
.:The percentage of
37        35
   X and  X are 25% and 75% respectively.

(c)
(i)Unlike in the Bohr Model, where the electron is treated as a particle in fixed orbits around the nucleus. In the Quantum Mechanical Model, the electron is treated mathematically as a wave. The Schröndinger equation/Model (Quantum Mechanical Model) allowed the electron to occupy a three-dimensional space.

(ii) Two other atomic models that attempt to explain the structure of an atom.
1. Rutherford atomic model and
2. Dalton's atomic model.

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