Question

Which of the following observations indicates that there is a small, dense, positively charged part in the center of an atom?

Some uncharged particles are scattered by a gold foil.
All uncharged particles are attracted towards a gold foil.
All positively charged particles pass straight through a gold foil.
Some positively charged particles bounce back from a gold foil.

Answer 1

The observation that some positively charged alpha particles bounced back from a gold foil during Rutherford's experiment indicates the presence of a small, dense, positively charged nucleus within the atom.

Step-by-step explanation:

The observation that indicates there is a small, dense, positively charged part in the center of an atom is that some positively charged particles bounce back from a gold foil. This was a key finding in the gold foil experiment conducted by Ernest Rutherford. When a beam of alpha particles, which are positively charged, was directed at a thin sheet of gold foil, most passed through but a few were deflected, and some even bounced back. This could only be explained by the existence of a positively charged nucleus at the center of gold atoms, which repelled the positively charged alpha particles upon close encounter.

Rutherford's experiment led to the conclusion that atoms have a nuclear model, with the majority of the mass and positive charge concentrated in a central nucleus, surrounded by a cloud of electrons. The bouncing of alpha particles directly back towards their source suggested the nucleus was both densely packed and contained a high positive charge, repelling the similarly charged alpha particles.

Answer 2

Option D

Step-by-step explanation:

Rutherford deduced that the atomic nucleus was positively charged because the alpha particles that he fired at the metal foils were positively charged, and like charges repel. Alpha particles consist of two protons and two neutrons, so they are positively charged. In Rutherford's experiments most of the alpha particles passed straight through the foil without being deflected. However, occasionally the alpha particles were deflected in their paths, and rarely the alpha particles were deflected backward at a 180 degree angle.

Since like charges repel, Rutherford concluded that the cause of the deflections of the positively charged alpha particles had to be something within the atom that was also positively charged. Rutherford concluded from his metal foil experiments that most of an atom is empty space with a tiny, dense, positively charged nucleus at the center that contains most of the mass of the atom.