AMU or atomic mass unit is a unit of mass used to express relative atomic masses. It is equal to 1/12 of the mass of an atom of the isotope carbon-12 and is equal to 1.66 033×10-27 kg. This unit superseded both the physical and a chemical mass unit based on oxygen-16 and is sometimes called the unified mass unit or the dalton.
Amadeo Avogadro (1776-1856) is an Italian chemist and physicist that proposed a correct molecular explanation for Gay-Lussac’s law of combining volumes. His work provided a simple way to determine atomic weights and molecular weights of gases. He is published a theory about the movement of particles in gases that became known as Avogadro’s Law.
Bohr atom is a model of the atom that explains emission and absorption of radiation as transitions between stationary electronic states in which the electron orbits the nucleus at a definite distance. The Bohr model violates the Heisenberg uncertainty principle since it postulates definite paths and moment for electrons as they move around the nucleus. Modern theories usually use atomic orbitals to describe the behaviour of electrons in atoms.
In the valence bond theory, a valence bond is a chemical bond formed by overlap of half-filled atomic orbitals on two different atoms.
Absolute zero is theoretically, the lowest attainable temperature. It is the energy at which the kinetic energy of atom and molecules is minimal and is equivalent to -273.15 °C.
Acid is a type of compound that contains hydrogen and dissociates in water to produce positive hydrogen ions. The reaction for an acid HA is commonly written:
In fact, the hydrogen ion (the proton) is solvated, and the complete reaction is:
This definition of acids comes from the Arrhenius theory. Such acids tend to be corrosive substances with a sharp taste, which turn litmus red and produce colour changes with other indicators. They are referred to as protonic acids and are classified into strong acids, which are almost completely dissociated in water, (e.g. sulphuric acid and hydrochloric acid), and weak acids, which are only partially dissociated (e.g. acetic acid and hydrogen sulphide). The strength of an acid depends on the extent to which it dissociates, and is measured by its dissociation constant.
In the Lowry-Brønsted theory of acids and bases (1923), the definition was extended to one in which an acid is a proton donor (a Brønsted acid), and a base is a proton acceptor (a Brønsted base). An important feature of the Lowry-Brønsted concept is that when an acid gives up a proton, a conjugate base is formed that is capable of accepting a proton.
Similarly, every base produces its conjugate acid as a result of accepting a proton.
For example, acetate ion is the conjugate base of acetic acid, and ammonium ion is the conjugate acid of ammonia.
As the acid of a conjugate acid/base pair becomes weaker, its conjugate base becomes stronger and vice versa.
A further extension of the idea of acids and bases was made in the Lewis theory. In this, a G. N. Lewis acid is a compound or atom that can accept a pair of electrons and a Lewis base is one that can donate an electron pair. This definition encompasses "traditional" acid-base reactions, but it also includes reactions that do not involve ions, e.g.
in which NH3 is the base (donor) and BCl3 the acid (acceptor).
Alpha particle is a helium nucleus emitted spontaneously from radioactive elements, both natural and manufactured. Its energy is in range 4-8 MeV and is dissipated in a very short path, i.e. a few centimetres of air or less than 0.005 mm of aluminium. As helium nucleus consists of two protons and two neutrons bound together as a stable entity the loss of an alpha particle involves a decrease in nucleon number of 4 and decrease of 2 in the atomic number, e.g.
A stream of alpha particles is known as an alpha ray or alpha-radiation.
Beta particle is a charged particle emitted from a radioactive atomic nucleus either natural or manufactured. The energies of beta particles range from 0 MeV to 4 MeV. They carry a single charge; if this is negative, the particle is identical with an electron; if positive, it is a positron.
An unstable atomic nucleus changes into a nucleus of the same mass number but different proton number with the emission of an electron and an antineutrino (or a positron and a neutrino)
Generalic, Eni. "Dalton%E2%80%99s atomic theory." Croatian-English Chemistry Dictionary & Glossary. 29 June 2022. KTF-Split. {Date of access}. <https://glossary.periodni.com>.
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