Summary 1. Particles and Radiation

Section 1:
-Particles and Radiation




Specific Charge


The specific charge of a particle is the ratio of its charge to its mass, given in coulombs per kilogram (Ckg -1)


𝐶ℎ𝑎𝑟𝑔𝑒 Particles Charges (C) Mass (kg)
𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝐶ℎ𝑎𝑟𝑒 =
𝑀𝑎𝑠𝑠
Proton +1.6 x10-19 1.67 x 10-27
Neutron 0 1.67 x 10-27
Electron -1.6 x 10-19 9.11 x 10-11


Calculating the specific charge of a carbon-12 atom:

 Mass of a nucleon (1.67 x 10-27) and the mass number of the carbon atom is 12.
o Thus: (1.67 x 10-27) x (12) = (2.004 x 10-26)
 The charge of a proton is (1.6 x 10-19) and the atomic number is 6
o Thus (6) x (1.6 x 10-19) = 9.6 x 10-19
 Therefore for the specific charge. (9.6 x 10-19) / (2.004 x 10-26) = 4.79 x 107 C Kg-1

Isotopes


Atoms with the same number of protons but different number of neutrons are isotopes. The number of neutrons
doesn’t affect the chemical properties of the atom but instead the stability of the atom.



Stable and Unstable Nuclei


Nuclei are positively charged, so keeping them stable requires a very strong force – unstable nuclei
become more stable by decaying.

Forces in the nucleus:

 There is an electromagnetic force that causes the positively charged protons in the nucleus to
repel each other.
 There are gravitational forces that cause all the nucleons to attract to each other.

The electromagnetic force is much greater than the gravitational force. Therefore, if there were only
these two forces acting on the protons, they would fly apart.