Engineering Chemistry S Datta

44 ENGINEERING CHEMISTRY
(iii) Mass (iii) 4 a.m.u.
1
(iii) of hydrogen
1836
atoms or 0.000548
a.m.u.
(iv) Charge (iv) Possess positive
charge of 2 units
= 9.6 × 10 –10 e.s.u. or
3.2 × 10 –19 coulomb.
(v) Velocity
(vi) Penetrating
power
(v) Nearly 1/10 the speed
of light or 20,000 to
30,000 km per sec.
(iv) Possess negative
charge of 1 unit
= 4.8 × 10 –10 e.s.u. or
1.6 × 10 –19 coulomb.
(v) 2.36 × 10 8 to 2.83 ×
10 8 m/sec.
(iii) No mass (0)
(iv) No charge (0)
(v) Nearly same as
light 3 × 10 8 m/sec.
(vi) Low (vi) Medium (vi) Maximum
It has been observed that heavier elements in which neutron-proton ratio (N/p) exceed
1.5 show radioactivity. These nuclei are unstable and emit spontaneously α, β, or γ-rays to give
daughter elements.
Nuclear Stability
1. Nuclei with 84 or more protons are radioactive.
2. Nuclei containing 2, 8, 20, 50, 82 and 126 protons or neutrons are more stable than
other nuclei containing different number of protons and neutrons. These numbers
are magic numbers.
3. Nuclei with even numbers of protons and neutrons are more stable than that with
odd numbers.
240
200
160
Mass number, A
120
80
40
0
10 30 50 70 90
Atomic number, Z
Fig. 3.1