Dictionary, Defintion, Meaning, What is Daltons Atomic Theory, De Brogile Equation, Daltons Law, Daniell Cell, Davy Lamp, D-block Elements

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Home >> Chemistry Dictionary >> Daltons Atomic Theory De Brogile Equation

Your Ad Here	D. Deuterium Dalton’s atomic theory. A theory of chemical combination. It involves the following postulates: (1) Elements consist of indivisible small particles (atoms). (2) All atoms of the same element are identical; different elements have different types of atom. (3) Atoms can neither be created nor destroyed. (4) ‘Compound elements’ (i.e. compounds) are formed when atoms of different elements join in simple ratios to form ‘compound atoms’ (i.e. molecules).
Dalton’s law. The total pressure of a mixture of gases or vapour is equal to the sum of the partial pressure of its components, i.e. the sum of the pressures that each component would exert if it were present alone and occupied the same volume as the mixture of gases. Strictly speaking, the principle is true only for ideal gases. P(Total) = P₁ + P₂ + P₃……
Daniell cell. A type of primary voltaic cell with a copper positive electrode and a negative electrode of a zinc amalgam. The zincamalgam electrode is placed in an electrolyte of dilute sulphuric acid or zinc sulphate solution in a porous pot, which stands in a porous pot, which stands in a solution of copper sulphate in which the copper electrode is immersed. While the reaction takes place ions move through the porous pot, but when it is not in use the cell should be dismantled to prevent the diffusion of one electrolyte into the other. The e.m.f. of the cell is 1.08 volts with sulphuric acid and 1.10 volts with zinc sulphate.	Your Ad Here
Davy lamp. An oil-burning miner’s safely lamp invented by Sir Humphry Davy (1778-1829) in 1816 when investigating firedamp (methane) explosions in coal mines. The lamp has a metal gauze surrounding the flame, which cools the hot gases by conduction and prevents ignition of gas outside the gauze. If firedamp is present it burns within the gauze cage, and lamps of this type are still used for testing for gas. D-block elements. The block of elements in the periodic table consisting of schandium, yttrium, and lanthanum together with the three periods of transition elements: tinanium to zinc, zirconium to cadmium, and hafnium to mercury. These elements all have two outer s-electrons and have d-electrons in their penultimate shell; i.e. an outer electron configuration of the form (n-1) d_xns₂, where x is 1 to 100.
Your Ad Here	Deacon process. A process which is used for making chlorine by oxidizing hydrogen chloride in air at 450°C using a copper chloride catalyst. Deactivation. These device whereby the chemical reactivity of a substance is diminished or entirely removed. For example, the catalytic activity of metals such as platinum or nickel for various hydrocarbon reactions may be completely removed or considerably reduced by the presence of trace amounts of catalyst poisons such as sulphur or mercury which cause deactivation of the catalyst.

Alternatively. In a photochemical reaction a molecule absorbs light. This results in it possessing more energy than an ordinary molecule and, consequently, more reactivity. However, collision of this activated molecule with another molecule may cause the former to lose its energy without reacting. The activated molecule is said to have undergone a deactivating collision and has itself become deviated.
De Broglie equation. In 1924 de Broglie suggested that the wavelength of electrons (λ) is given by the equation:
λ= (h/p) = (h/mv) where h = planks constant, m = mass of electron, v = velocity and p = momentum of the electron. Wavelengths calculated from this equation are often called de Broglie wavelengths.
Debye. A unit of electric dipolemoment equal to 3.33564 x 10^-20 coulomb meter. It is used in expressing the dipolemoment of molecules.
Debye-Huckel theory. The activity coefficient of an electrolyte depends markedly upon concentration. In dilute solutions, due to the Coloumb forces of attraction and repulsion, the ions tend to surround themselves with an ‘atmosphere’ of oppositely charged ions. Debye and Huckel showed that it was possible to explain the abnormal activity coefficient at least for very dilute solutions of electrolytes.
Decane. (C₁₀H₂₂) A liquid paraffin hydrocarbon b.p. 174.1°C which is found in various someric form.
Deca. Symbol da. A prefix used in the metric system to denote ten time. For example, 10 coulombs = 1 decacoulomb (daC).

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