CHEMISTRY GLOSSARY

second    →   sekunda

Second (s) is the SI base unit of time.

The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels (F = 4, m_F = 0 to F = 3, m_F = 0) of the ground state of the caesium 133 atom.

second-order reactions    →   reakcije drugog reda

Second-order reaction is a reaction with a rate law that is proportional to either the concentration of a reactant squared, or the product of concentrations of two reactants.

For a general unimolecular reaction,

The reaction rate expression for a second order reaction is

If assumed that the concentration of reactant A is [A]_o at t=0 and [A] at time T, the variables in the rate equation and integrate can be separated. The integrated rate law for a second-order reaction can be easily shown to be

sedimentary rocks    →   sedimentne stijene

Sedimentary Rocks are formed by the accumulation and subsequent consolidation of sediments into various types of rock. There are three major types of sedimentary rocks:

Biogenic sedimentary rocks are formed from organic processes when organisms use materials dissolved in water to build a shell or other skeletal structure.

Clastic sedimentary rocks are composed directly of the sediments or fragments from other rocks.

Chemical sedimentary rocks are formed through evaporation of a chemical rich solution.

Based on their sizes, sediment particles are classified, based on their size, into six general categories:

• boulder (>256 mm)
• cobble (64 - 256 mm)
• gravel (2 - 64 mm)
• sand (1/16 - 2 mm)
• silt (1/256 - 1/16 mm)
• clay (<1/256 mm)

sedimentation    →   sedimentiranje

Sedimentation is a process of separating specifically heavier, suspended matter, than the solution is. Solid matter settles on the bottom of the vessel and the liquid above it is poured off. The settling zone is the largest portion of the sedimentation basin. This zone provides the calm area necessary for the suspended particles to settle. The sludge zone, located at the bottom of the tank, provides a storage area for the sludge before it is removed for additional treatment or disposal.

selenium    →   selenij

Selenium was discovered by Jöns Jakob Berzelius (Sweden) in 1817. The origin of the name comes from the Greek word selene meaning moon. It is soft metalloid similar to sulfur. Ranges from grey metallic to red glassy appearance. Unaffected by water. Soluble in alkalis and nitric acid. Burns in air. Toxic by inhalation or ingestion. Selenium is obtained from lead, copper and nickel refining. Conducts electricity when struck by light. Light causes it to conduct electricity more easily. It is used in photoelectric cells, TV cameras, xerography machines and as a semiconductor in solar batteries and rectifiers. Also colours glass red.

serine    →   serin

Serine is neutral amino acids with polar side chains. It is one of two hydroxyl amino acids. Both are commonly considered to by hydrophilic due to the hydrogen bonding capacity of the hydroxyl group. Serine often serves as a nucleophile in many enzyme active sites, and is best known for its role in the serine proteases. Serine is a site of phosphorylation and glycosylation which is important for enzyme regulation and cell signaling. It is not essential to the human diet, since it is synthesized in the body from other metabolites, including glycine.

• Abbreviations: Ser, S
• IUPAC name: 2-amino-3-hydroxypropanoic acid
• Molecular formula: C₃H₇NO₃
• Molecular weight: 105.09 g/mol

sigma bond    →   sigma veza

Most single bonds are sigma bonds (σ-bond). In the valence bond theory, a sigma bond is a valence bond that is symmetrical around the imaginary line between the bonded atoms.

significant figures    →   značajne znamenke

Measurements are not infinitely accurate: we must estimate measurement uncertainty. The number of significant figures is all of the certain digits plus the first uncertain digit.

Rules for significant figures:

1. Disregard all initial zeros.
2. Disregard all final zeros unless they follow a decimal point.
3. All remaining digits including zeros between nonzero digits are significant.

In addition and subtraction, the number of significant figures in the answer depends on the original number in the calculation that has the fewest digits to the right of the decimal point.

In multiplication and division, the number of significant figures in a calculated result is determined by the original measurement that has the fewest number of significant digits.

In a logarithm of a number, keep as many digits to the right of the decimal point as there are significant figures in the original number.

In an antilogarithm of a number, keep as many digits as there are digits to the right of the decimal point in the original number.

silicon    →   silicij

Silicon was discovered by Jöns Jacob Berzelius (Sweden) in 1824. The origin of the name comes from the Latin word silicis meaning flint. Amorphous form of silicon is brown powder; crystalline form has grey metallic appearance. Solid form unreactive with oxygen, water and most acids. Dissolves in hot alkali. Silica dust is a moderately toxic acute irritant. Silicon makes up major portion of clay, granite, quartz and sand. Commercial production depends on a reaction between sand (SiO₂) and carbon at a temperature of around 2200 °C. Used in glass as silicon dioxide (SiO₂). Silicon carbide (SiC) is one of the hardest substances known and used in polishing. Also the crystalline form is used in semiconductors.

silver    →   srebro

Silver has been known since ancient times. The origin of the name comes from the Latin word argentum meaning silver. It is silvery-ductile and malleable metal. Stable in water and oxygen. Reacts with sulfur compounds to form black sulfides. Silver is found in ores called argentite (AgS), light ruby silver (Ag₃AsS₃), dark ruby silver (Ag₃SbS₃) and brittle silver. Used in alloys for jewellery and in other compounds for photography. It is also a good conductor, but expensive.