The Nuclear model of the atom.
The nuclear model of the atom is a model which attempts to describe the structure of the atom by Ernest Rutherford how shot positive alpha particles a thin layer of gold foil. Rutheford believed that the alpha particles would tear straight through the gold foil with little or no deflection. Some particles however, rebounded straight back at him. It was as if he had held a piece of tissue paper at an oncoming cannon ball and have it rebound off the paper! To explain these results Rutherford proposed the nuclear model of the atom.
The atom is
- composed of a very dense positively charged nucleus
- made up mostly of empty space
- surrounded by negatively charged orbiting electrons.
The nucleus itself was found to be composed of positive protons and neutral neutrons.
The term nuclear mass is a whole number and tells us the number of particles in the nucleus of an atom. That is the number of protons and neutrons.
The number of protons in an atom determines the identity of an element. This number is also called the Atomic number.
Neutrons provide nuclear stability to the nucleus. If the proton to neutron ratio falls outside a certain band the nucleus becomes unstable and is said to be radioactive.
In a neutral atom the number of negative electrons is equal to the number of positive protons.
Sometimes atoms of the same element (same number of protons) vary in the number of neutrons in the nucleus. These atoms are called isotopes. For example Carbon-12, Carbon-13 and Carbon-14 all contain six protons. However, the number of neutrons is respectively, 6, 7 and 8.
Isotopes with an unstable nucleus are called radioisotopes. eg. Carbon-14
Radioisotopes emit ionising radiation in the form of alpha, beta and or gamma radiation. Ionising radiation removes the electrons from an atom producing positive ions.