Atoms - tiny wonders to explore
Atomic radii: 1-3 Å (1e-10 m)
Nucleus radii: 1~3 fm (fermi or femtometer 1e-15 m)
Goldstein discovered canal rays (Kanalstrahlen) in 1886
Wien and Thomson saw positive rays moving in opposite direction of cathode
- Rutherford concluded that these are nuclei of H atoms, and he called
- Properties of protons:
charge, same as electron but positive
mass 1.67262314e-27 kg, mass of H less the electron mass
magnetic moment, 2.7928474 nuclear magnetic moment
Rutherford speculated existence of neutral particles in atomic nuclei.
- Bothe, Becker, Joliot, Curie and Chadwick observed some very penetrating
particles when they bombarded beryllium with alpha particles.
The reaction is now known as
Be + a = C + n + Energy
James Chadwick (1891-1974) discovered and confirmed neutrons from the
B + n = Li + a + Energy
Deuterium, an isotope of hydrogen
Many scholars speculated the existence of isotopes
- Isotopes are atoms of the same element, but their masses are different.
|Properties of H2, HD, and D2
|Property||H2 ||HD ||D2
|Tripple point /K||13.96 ||16.60 ||18.73
|Boiling point /K||20.39 ||22.13 ||23.67
- Nuclei of isotopes contain the same number of protons, but
different number of neutrons
Harold C. Urey (1893 - 1981) distilled H2 to get D2
The abundance of D in hydrogen is 0.014%
Electrolysis decomposes H2O faster than D2O,
and the remaining water has a higher concentration of HDO and D2O
than ordinary water (production of heavy water during WW II)
Another isotope of H is tritium, T. Its nucleus contains 2 n and 1 p
D is stable, but T emits beta particles
A nuclide is represented by
M, mass number; Z, atomic number (often omitted);
N = M - Z is the number of neutrons
For example, 1H, 2H, and 3H are
H, D, and T
Atomic weight average mass of all isotopes of an element.
Atomic mass of a nuclide is the mass of an isotope or nuclide.
Protons and neutrons are composed of something smaller called quarks.
No individual quark has been observed, but theory and experiments
suggest that proton consists of 2 up quarks and 1 down quark.
A neutron consists of 1 up quark and 2 down quarks.
The standard model
|Fundamental particles of the standard model
|Generation: ||First ||Second ||Third
|Quarks ||u, d ||c, s ||b, t