أكاديميا - كولنز - معاجم الجيب العلمية - الكيمياء - انكليزي - فرنسي - عربي الحرف ١_ v

Academia - Collins - Pocket Scientific Dictionaries - Chemistry - English - French - Arabic Letter 1_ V


vacuum
video m

Emptiness. Vacuum is a vacuum in which there are no atoms or molecules. It is impossible to achieve “complete” vacuum, but we are talking about “partial” vacuum when the pressure is very low. The pressure in space is low, which is why it is thought of as a vacuum.


valency
valence f

Equivalence. Valency can be thought of, simply put, as combining power, the usual number of bonds an atom forms when making compounds. More precisely, the valency of an element is the number of electrons an element needs to form a compound or radical. Electrons can be given to another element, taken from an element, or shared.

Some elements always have the same stoichiometry, for example: hydrogen = 1, oxygen = 2 except in peroxides), sodium = 1, magnesium = 2.

Examples:

Sodium has a valency of one. Sodium gives up one electron when it forms the ion sodium Na+, as in NaCl.

Oxygen has two valences, and oxygen accepts two electrons when it forms the 02-oxide moiety or when it forms covalent compounds, such as SO2, CO2, and N2O.
Hydrogen and bromine have a valency of the same. They both give up one electron to make the covalent H-Br bond when they form hydrogen bromide. For single asymmetric transition elements. For example, the valency of iron = 2 and 3, of cobalt = 2 and 3, and of copper = 1 and 2. The following two tables contain the valency of some common elements and electrolytes:

Positive values

+ 1
Litium +L1
Sodium +Na
Potassium +K
Silver + Ag
Ammonium +NH4
Hydrogen +H
Copper ( I ) + Cu

+ 2
Calcium +Ca2
Magnesium +Mg2
Zinc +Zn2
Iron (III) +Fe2
Lead +pb2
Copper (II) +Cu2

+ 3
Aluminum +Al3
Iron Fe3+ (III)


Negative values

- 1
Fluoride - F
Chloride - CI
Bromide - Br
Iodide - I
Hydroxide - OH
Nitrogen -NO 3

- 2
Sulfide -S2
Oxide -O2
Carbonate CO2-/3
Sulphate 4/-SO2

- 3
Phosphate 4/-PO3


vanadium
vanadium m

Vanadium is a transition metal. It is mainly used in the production of valuable vanadium alloys - steel due to its high tensile resistance and hardness. These mixtures often contain chromium or manganese, as well as vanadium.

Vanadium oxide (V205) is the catalyst used in the contact process.


Van der Waals' forces
forces fpl de van der waal

Van der Waals forces. Weak forces between atoms result from the movement of electrons within
Atoms and elements that only have these forces to hold them together, such as inert gases, have very low melting and boiling points.


vapour
vapor f

Vapor atoms or molecules are in a gaseous state, but below their critical temperature, which is the temperature above which a liquid cannot exist.
For example: When water evaporates from a pot in the house, it is the water vapor that is formed, not the steam of boiling water.


!
vinaigre m

Vinegar is a solution made by the action of bacteria in wine, apple juice, or other fruit. Vinegar contains about 4 percent ethanoic acid, or it is widely used in the food industry to preserve food.