Who was the first one to propose a model for the structure of an atom ?
J. J. Thomson
J. J. Thomson proposed the first model of atomic structure — option 4.
The sequence of models. Dalton had treated the atom as an indivisible solid sphere, with no internal structure at all. Once Thomson discovered the electron in 1897, an internal structure had to be accounted for, and he supplied the first :
| Year | Scientist | Model |
|---|---|---|
| 1904 | J. J. Thomson | “Plum pudding” or watermelon model — a sphere of positive charge with electrons embedded in it |
| 1911 | Ernest Rutherford | Nuclear model — a tiny dense positive nucleus with electrons moving around it |
| 1913 | Niels Bohr | Electrons confined to fixed orbits of definite energy, emitting or absorbing energy only on jumping between them |
| 1920s | Schrödinger and others | Quantum mechanical model — orbitals of probability rather than orbits |
Why Thomson’s model failed. Rutherford’s gold-foil experiment fired alpha particles at a thin sheet of gold. Most passed straight through, but a very small fraction were deflected through large angles and a few came almost straight back — “as if you had fired a fifteen-inch shell at a piece of tissue paper and it came back and hit you”. A diffuse pudding of positive charge could not deflect a heavy alpha particle so sharply; only a concentrated, massive positive centre could. Hence the nucleus.
Why Rutherford’s model in turn failed is worth knowing too: classical electromagnetism requires an accelerating charge to radiate energy, so an orbiting electron should spiral into the nucleus within a fraction of a second. Bohr resolved this by postulating stationary orbits in which the electron does not radiate — the first use of quantum ideas in atomic structure.
E. Goldstein, option 1, discovered canal rays in 1886, which led to the identification of the proton, but he proposed no model of the atom.
Hence, the answer is J. J. Thomson.
Important Questions from Structure of Atom
- How many moles of He atoms are present in its 20 u mass ?
Which of the following electron transition in hydrogen atom will require largest amount of energy?
A species having 8 electrons in the third shell is very reactive while the other species having 8 electrons in the third shell is very inactive they are :
Which of the following is the general formula for saturated hydrocarbons?
Which one of the following is the average atomic mass of chlorine atom?
