CHEMISTRY GLOSSARY

neutron    →   neutron

Neutron is an elementary particle on spin 1/2 and zero charge. The free neutron has an average lifetime of 887 seconds. Neutrons and protons, which are collectively called nucleons, are the constituents of the nucleus.

chlorinity    →   klorinitet

Originally chlorinity (symbol Cl) was defined as the weight of chlorine in grams per kilogram of seawater after the bromides and iodides had been replaced by chlorides. To make the definition independent of atomic weights, chlorinity is now defined as 0.3285233 times the weight of silver equivalent to all the halides.

The Mohr-Knudsen titration method served oceanographers for more than 60 years to determine salinity from chlorinity. This modification of the Mohr method uses special volumetric glassware calibrated directly in chlorinity units. The Mohr method uses potassium chromate (K₂CrO₄) as an indicator in the titration of chloride ions chloride (plus a small amount of bromide and iodide) with a silver nitrate (AgNO₃) standard solution.

The other halides present are similarly precipitated.

A problem in the Mohr titration was that silver nitrate is not well suited for a primary standard. The Danish physicist Martin Knudsen (1871-1949) suggested that a standard seawater (Eau de mer Normale or Copenhagen Normal Water) be created and distributed to oceanographic laboratories throughout the world. This water was then used to standardize the silver nitrate solutions. In this way all chlorinity determinations were referred to one and the same standard which gave great internal consistency.

The relationship between chlorinity Cl and salinity S as set forth in Knudsen's tables is

In 1962, however, a better expression for the relationship between total dissolved salts and chlorinity was found to be

Einstein equation    →   Einsteinova jednadžba

Einstein equation is the mass-energy relationship introduced by Albert Einstein in 1905 in the form E = mc², where E is a quantity of energy, m its mass, and c is the speed of light. It presents the concept that energy possesses mass.

nucleon    →   nukleon

Nucleon is a collective term for the proton and neutron.

nuclide    →   nuklid

Nuclide is a species of atoms in which each atom has identical atomic number Z and identical mass number A. For example, a carbon-14 (C-14 or ¹⁴C) nuclide is the nucleus of a carbon atom, which has six protons and eight neutrons.

radioactivity    →   radioaktivnost

Radioactivity is capability of a spontaneous decay of an atom. In this way a new atom type is formed and radioactive radiation is released. An atom can emit three types of radioactive radiation: positive α-radiation, negative β-radiation and electrically neutral γ-radiation. During radioactive decay one element never emits all types of radiation at the same time.

electron affinity    →   elektronski afinitet

Electron affinity (E_A) is the energy change occurring when an atom or molecule gains an electron to form a negative ion. For an atom or molecule X, it is the energy released for the electron-attachment reaction

This is often measured in electronvolts. Alternatively, the molar enthalpy change, ΔH, can be used.

explosive    →   eksploziv

Explosive is a compound or mixture that, when ignited or detonated, undergoes rapid violent chemical reaction that produces large amount of gas and heat, accompanied by light, sound and a high pressure shock wave.

fission    →   fisija

Fission is a nuclear reaction in which an atomic nucleus breaks into smaller nuclei of comparable mass, releasing a large amount of energy.

halogens    →   halogeni elementi

Halogens are the elements fluorine (F) chlorine (Cl), bromine (Br), iodine (I), and astatine (At). They are non-metals, and make up part of the 17 group in the periodic table. Compounds of these elements are called halogenides or halides.

The halogens all have a strong unpleasant odour and will burn flesh. They do not dissolve well in water. The five elements are strongly electronegative. They are oxidising agents, with fluorine being the strongest and astatine being the weakest. They react with most metals and many non-metals.

Halogens form molecules which consist of atoms covalently bonded. With increasing atomic weight there is a gradation in physical properties. For example: Fluorine is a pale green gas of low density. Chlorine is a greenish-yellow gas 1.892 times as dense as fluorine. Bromine is a deep reddish-brown liquid which is three times as dense as water. Iodine is a grayish-black crystalline solid with a metallic appearance. And astatine is a solid with properties which indicate that it is somewhat metallic in character.