In the modern atomic theory, an atom of a certain element is defined by the number of protons it has in its nucleus. This number is called the atomic number of that element, and it is what distinguishes one element from another. For instance, hydrogen has only one proton while iron has twenty-six protons. Similarly, the number of neutrons that an atom has is also different from one to the other, and it is calculated by subtracting the atomic number from the mass number of the element.
Iron, with the chemical symbol Fe, is a metal that belongs to the first transition series and group 8 of the periodic table. It is one of the most abundant elements in the Earth. It is found in many minerals, especially sulphur and oxygen, and it is used to produce iron-containing alloys such as steel. It is also a critical dietary requirement in humans, as it is needed for hemoglobin formation and blood circulation.
The neutron is a particle that resides in the nucleus of an atom and has no charge. It was discovered by scientist Chadwick in 1932. It has a mass of 1.674 x 10-27 kg and is represented by the symbol N. Neutrons are the permanent core particles of an atom and they contribute significantly to its weight.
An atom of iron can exist in its ionic form as either Fe2+ or Fe3+. Fe2+ is formed by the loss of three valence electrons, so it has 26 - 3 = 23 electrons. The other ion, Fe3+, is formed by the loss of five valence electrons and it has 26 - 5 = 21 electrons.