Question

What discoveries were made by J. J. Thomson, Henri Becquerel, and Lord Rutherford? How didDalton's model of the atom have to be modified to account for these discoveries?

Short answer

The subatomic particles smaller than an atom discovered by Rutherford, Thomson and Becquerel. Electron was discovered by J. J. Thomson. Radioactivity discovered Becquerel.

Step-by-step solution

Electron and Radioactivity discovery

Electrons was discovered by J. J. Thomson whereas radioactivity was discovered by Becquerel. The nuclear model of the atom postulated by Rutherford.

Dalton's model of the atom have to be modified to account for these discoveries

Atoms are the smallest particles said by the Dalton. The subatomic particles smaller than an atom discovered by Rutherford, Thomson and Becquerel. There may be a modification in Dalton’s model. The modification is comprised of subatomic particles.

Conclusion

The subatomic particles smaller than an atom discovered by Rutherford, Thomson and Becquerel. Electron was discovered by J. J. Thomson. Radioactivity discovered Becquerel.