In the early 20th century, Ernest Rutherford proposed the nuclear model of the atom to replace J. J. Thomson's plum pudding model. Describe two major differences between Rutherford's nuclear model and the plum pudding model.

Niels Bohr later adapted Rutherford's nuclear model by considering how electrons behave when they absorb or emit electromagnetic radiation. Describe how Bohr's model of electron arrangement differed from Rutherford's description of electrons.

In 1869, Dmitri Mendeleev published his periodic table. He arranged the elements primarily in order of atomic weight, but swapped the positions of some pairs of elements. A critic suggested that Mendeleev should have ordered the elements by the number of protons in their atoms instead. Explain why Mendeleev could not have used the number of protons to order his table.

State the scientific reason why Mendeleev decided to reverse the order of some pairs of elements.