Alpha particles come from the decay of the heaviest radioactive elements, such as uranium, radium and polonium.

Alpha particles are subatomic fragments consisting of two neutrons and two protons. Alpha radiation occurs when the nucleus of an atom becomes unstable (the ratio of neutrons to protons is too low) and alpha particles are emitted to restore balance.

Beta radiation

In Rutherford’s experiment, when an alpha particle hit the zinc sulphide screen, the screen would emit light. Once they struck the screen, light would be emitted, indicating that an alpha particle had been detected.

Rutherford’s experiment showed the existence of a nuclear atom – a small, positively-charged nucleus surrounded by empty space and then a layer of electrons to form the outside of the atom. Most of the alpha particles did pass straight through the foil. The atom being mostly empty space.

Rutherford’s gold foil experiment showed that the atom is mostly empty space with a tiny, dense, positively-charged nucleus. Based on these results, Rutherford proposed the nuclear model of the atom.

Rutherford’s model of atom was wrong because the presence of electrostatic attraction between the nucleus and the electrons. The electrons should fall into the nucleus, but they didn’t. When this model was applied to atoms other than hydrogen it did not work. Electrons do not move around the nucleus in circular orbits.

Dalton model

The main problem with Bohr’s model is that it works very well for atoms with only one electron, like H or He+, but not at all for multi-electron atoms. Bohr’s model breaks down when applied to multi-electron atoms. It does not account for sublevels (s,p,d,f), orbitals or elecrtron spin.

But there was good evidence he was right: the electrons in his model lined up with the regular patterns (spectral series) of light emitted by real hydrogen atoms. Bohr’s theory that electrons existed in set orbits around the nucleus was the key to the periodic repetition of properties of the elements.

Bohr’s model allows classical behavior of an electron (orbiting the nucleus at discrete distances from the nucleus. The atomic number or proton number (symbol Z) of a chemical element is the number of protons found in the nucleus of every atom of that element.

an electromagnetic spectrum consisting of discrete lines, usually characteristic of excited atoms or molecules.

atoms is known as a line spectrum, because the radiation (light) emitted consists of a series of sharp lines. The simplest spectra are those of atomic hydrogen and the alkali atoms (e.g., lithium, sodium,…

There are three general types of spectra: continuous, emission, and absorption.