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Mass number

An element’s mass number (A) is the sum of the number of protons and the number of neutrons. The small contribution of mass from electrons is disregarded in calculating the mass number. This approximation of mass can be used to easily calculate how many neutrons an element has by simply subtracting the number of protons

Atomic number

Neutral atoms of an element contain an equal number of protons and electrons. The number of protons determines an element’s atomic number (Z) and distinguishes one element from another. For example, carbon’s atomic number (Z) is 6 because it has 6 protons. The number of neutrons can vary to produce isotopes, which are atoms of


Carbon [symbol C] (from Latin: carbo “coal”) is a nonmetallic and tetravalent (rarely bivalent) chemical element—making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Individual carbon atoms have an incomplete outermost electron shell. With an atomic number of 6 (six electrons and six protons), the first



Latent heat

Latent heat is the quantity of heat required to bring about a change of state of a unit mass of a substance from solid to liquid (latent heat of fusion) or from liquid to gas (latent heat of vaporization or of condensation) or from solid to gas directly (latent heat of vaporization) without change of temperature


Superfluids have many unusual properties. They behave like typical components of solutions, with all the properties associated with normal fluid and superfluid components. Therefore it is impossible to set a temperature gradient in a superfluid, as it is impossible to set a potential difference in a superconductor. Superfluidity was discovered by Pëtr Leonidovič Kapica, John


Superfluidity is a special quantum state of matter in which a substance (called superfluid) flows with zero viscosity (without loss of kinetic energy), by the absence of entropy and by having infinite thermal conductivity. The superfluids, if placed in a closed path, can flow infinitely without friction.


Chemistry (from kemà, the book of Egyptian art secrets, from the Arabic word al-kīmīā, الكيمياء) is the science that studies the composition of matter and its behavior based on this composition, also called “central science“ because it connects other natural sciences, such as astronomy, physics, materials sciences, biology, and geology.


The glass is a non-equilibrium, non-crystalline condensed state of matter that exhibits a glass transition. The structure of glasses is similar to that of their parent supercooled liquids (SCL), and they spontaneously relax toward the SCL state. Their ultimate fate, in the limit of infinite time, is to crystallize. Glasses are also known as amorphous solids. The boundary between the

Law of multiple proportions

The law of multiple proportions is a chemical law obtained experimentally by the English chemist, physicist and meteorologist John Dalton. Many combinations of elements can react to form more than one compound. In such cases, this law states that the weights of one element that combine with a fixed weight of another of these elements

Law of definite proportions

Joseph Proust (1754-1826) formulated the law of definite proportions (also called the Law of Constant Composition or Proust’s Law). This law states that if a compound is broken down into its constituent elements, the masses of the constituents will always have the same proportions, regardless of the quantity or source of the original substance. Joseph Proust based this

Mass spectrometry

Mass spectrometry (MS) is an analytical technique useful for measuring the mass-to-charge ratio of ions of one or more molecules present in a sample. These measurements can often be used to calculate the exact molecular weight of the sample components as well. Mass spectrometry is used in many different fields and is applied to pure

Electron affinity

The electron affinity of an element is a measurable physical quantity, namely, the energy released or absorbed when an isolated gas-phase atom acquires an electron, measured in kJ/mol. We must be careful not to confuse electron affinity with electronegativity.

Chemical energy

Chemical energy is the potential energy stored in the bonds of chemical compounds to undergo a transformation through a chemical reaction to transform other chemical substances. It varies due to the formation or breaking of chemical bonds of any kind in the chemical elements involved in chemical reactions. An example of chemical potential energy is the


A solid is a state of matter in which atoms or molecules are tightly bound together by powerful forces thereby creating a rigid body (with a defined geometric shape and volume). The formation of a solid occurs with the establishment of bond forces between the atoms, of such intensity as to overcome the energy of thermal agitation.


In liquids, the atoms or molecules are not as tightly bound as in solids, and due to that, they have some freedom to move around. The liquid state is a condensed state of matter, because even in it, as in solids, the particles are linked (weakly) to each other. On the other hand, as liquids and


Gas is aeriform whose temperature is higher than the critical temperature; as a result, gases cannot be liquefied without first being cooled, unlike vapors. Gas is a fluid that has no volume of its own (tends to occupy all the volume at its disposal) and that is easily compressible. A gas is one of the four


Biogas is a mixture of different gases produced by anaerobic decomposition (with methanogen or anaerobic organisms), or fermentation, of biomass – organic material (including animal dung, human sewage, food waste, crop residues, and industrial and municipal wastes). Biogas is a renewable energy source. It is composed primarily of methane (up to 60%), which is the combustible component, carbon dioxide, and