What is an atom? Definition
Anything, person or animal we come into contact with every day is made up of atoms. Do you know what they are? Atoms , in a nutshell, are tiny particles that, when combined, form existing materials. The term atom comes from the Greek atomos and means “indivisible”. In fact, it represents the smallest part of an element that does not undergo alterations during a chemical reaction. However, it can undergo physical transformations , such as fission, disintegration, excitation.
What is an atom? Definition
Anything, person or animal we come into contact with every day is made up of atoms. Do you know what they are? Atoms , in a nutshell, are tiny particles that, when combined, form existing materials. The term atom comes from the Greek atomos and means “indivisible”. In fact, it represents the smallest part of an element that does not undergo alterations during a chemical reaction. However, it can undergo physical transformations , such as fission, disintegration, excitation.
For further information: The structures of the atom
How is an atom formed? Structure
An atom is made up of a central part called the nucleus , in which there are protons (positive charges) and neutrons (neutral charges). Around the nucleus rotate some negatively charged particles, called electrons . Atoms are differentiated from each other based on the number of protons, neutrons and electrons. An atom must be electrically neutral, so the atomic number (number of protons), indicated by the letter Z, is equal to the number of electrons. The mass number , indicated by the letter A, is the sum of the protons and neutrons. The number of neutrons found in the nucleus is therefore calculated with the difference between the mass number and the atomic number.
Atomic models
Through various scientific discoveries, the modern atomic theory was reached . In the early nineteenth century, John Dalton proposed a theory of the nature of matter, called Dalton’s Theory , based on the concept that matter is made up of very small particles called atoms, which cannot be created, transformed or divided. Subsequently, some scientists proposed atomic models.
Thomson model
According to Thomson, the atom is made up of a sphere formed by protons (positive charges), in which electrons are dispersed.
Rutherford model
For Rutherford, Thomson’s model is not convincing: he therefore proposes a model of an atom with a small, dense nucleus at the centre, made up mainly of protons, while the electrons are located in the surrounding space.
Bohr model
Bohr then proposed a new atomic model, with electrons describing circular orbits (called stationary orbits) around the nucleus. Read more: Bohr Atom: Summary
Sommerfeld and Pauli model
After Bohr, Sommerfeld discovered other orbits, the elliptical ones, thus introducing a secondary quantum number, l, and a magnetic quantum number, m. Pauli, in 1924, introduced a fourth quantum number, the spin quantum number.
