When alpha-particles are sent through a thin metal foil, most of them go straight through the foil because most of the atom is empty. This is known as the Rutherford's gold foil experiment, which was conducted by Ernest Rutherford in 1911.

The experiment involved shooting alpha-particles, which are positively charged particles consisting of two protons and two neutrons, at a thin sheet of gold foil. Rutherford expected the alpha-particles to pass through the foil with minimal deflection, as he believed in the widely accepted "plum pudding" model of the atom, where positive charge was spread uniformly throughout the atom with electrons embedded in it. However, the results of the experiment were surprising and led to the development of the nuclear model of the atom.

Explanation:

1. Plum Pudding Model:
- The plum pudding model, proposed by J.J. Thomson, suggested that atoms were composed of a positively charged "pudding" with negatively charged electrons embedded in it.
- According to this model, the positive charge was spread out uniformly throughout the atom, making it consistent with a solid sphere.

2. Rutherford's Experiment:
- Rutherford's experiment involved shooting alpha-particles at a thin sheet of gold foil.
- Alpha-particles are positively charged and have relatively large mass compared to electrons.
- Rutherford expected the alpha-particles to pass through the gold foil with minimal deflection, as predicted by the plum pudding model.

3. Observations:
- Most of the alpha-particles did pass through the foil with minimal deflection, as expected.
- However, a small fraction of the alpha-particles were deflected at large angles, and some even bounced back in the direction they came from.

4. Nuclear Model of the Atom:
- Rutherford's observations led him to conclude that the plum pudding model was incorrect.
- He proposed a new model, now known as the nuclear model of the atom.
- According to this model, atoms have a tiny, dense, positively charged nucleus at the center, and the electrons orbit the nucleus.

5. Explanation of Observation:
- Most of the alpha-particles pass straight through the foil because most of the atom is empty space.
- The positively charged nucleus is very small compared to the size of the atom, and the electrons are located far away from the nucleus.
- Therefore, the chances of an alpha-particle colliding with the nucleus or an electron are very low, resulting in most of the alpha-particles passing through the foil without any deflection.

In conclusion, alpha-particles go straight through a thin metal foil in the Rutherford's gold foil experiment because most of the atom is empty space, and the chances of an alpha-particle colliding with the tiny, dense nucleus or an electron are very low. This experiment provided evidence for the nuclear model of the atom, where the positive charge is concentrated in a small nucleus at the center of the atom, and the electrons orbit the nucleus.