For the great majority of atoms, it was found that the atomic mass (in atomic ma
ID: 1538902 • Letter: F
Question
For the great majority of atoms, it was found that the atomic mass (in atomic mass unit, u) is close to twice of the atomic number. (a) Looking up the periodic table (see the inside of the back cover of our text book!), verify whether this observation by computing the ratio f = atomic mass in u/atomic number for 9 elements of Z = 10, 20, 30, 40, ..., 90. What are the values f's those 9 elements? Are they consistent among 9 elements? (b) In terms of the mass number A, your result from (a) should show A ~ 2Z. Check whether it is true. What does this mean for the number of neutron N in the relation to the proton(or electron) number Z?Explanation / Answer
a) atomic number Z atomic mass A A/Z
10 20.179 2.179
20 40.078 2.0039
30 65.38 2.179
40 91.224 2.2806
50 118.710 2.3742
60 144.242 2.404
70 173.045 2.472
80 200.592 2.5074
90 232.0377 2.5781
100 257 2.57
The value starts near 2 and gradually increases to 2.57
b) Now, A is approximately equal to 2Z
NUmberof neutrons = A - Z = 2Z - Z = Z
NUmber of protons = Z
NUmber of electrons = Z
So all the number of subartomic particles are in close numbers to each other