aldose

A monosaccharide with an aldehyde function (-CHO). Glyceraldehyde, ribose, glucose, mannose and galactose are aldoses

atom

An atom is the smallest unit of an element . The atom consists of a nucleus and electrons which orbit the nucleus

atomic mass

Atomic mass is the correct name for the more commonly used term atomic weight
The atomic mass of an element is the weighted aveverages of the masses (measured in atomic mass units) of all natural isotopes of the element.
For example magnesium has 3 naturally occuring isotopes:

• Mg-24, 78.99 %
• Mg-25, 10.00 %
• Mg-26, 11.01 %

Since Mg has an atomic number of 12, we know its nucleus has 12 protons. Thus, the atomic mass (atomic weight) of naturally occuring Mg is : M_Mg = 0.7899 x (12 x 1.00728 amu + 12 x 1.00867 amu + 12 x 0.00055)
+ 0.1000 x (12 x 1.00728 amu + 13 x 1.00867 amu + 12 x 0.00055)
+ 0.1101 x (12 x 1.00728 amu + 14 x 1.00867 amu + 12 x 0.00055)
- 0.215976 amu ( mass defect) = 24.30500 amu
where 1.00728 amu = mass of a proton, 1.00867 amu = mass of a neutron, 0.00055 amu = mass of an electron and 0.215976 amu is mass equivalent of the energy released in the formation of the Mg nucleus from protons and neutrons (see Chemistry Review )

atomic mass unit

Since atoms are very small their mass is not expressed in gram (e.g. the mass of a carbon atom having 6 protons, 6 neutrons and 6 electrons is 1.992x10^-23 g . A relative scale is used where the carbon 12 isotope (6 protons, 6 neutrons, 6 electrons) has been assigned the value of 12.000 atomic mass units (amu). Thus, 1 amu = 1.6605x10^-24 g.

atomic number

The atomic number (Z) of an atom or an element represents the number of protons of the atom/element. For example carbon has 6 protons, thus, its atomic number Z=6. Oxygen, with its 8 protons has Z=8. See also mass number

atomic weight

Atomic weight is used interchangeably with atomic mass

chemical bonds

Covalent Bond: Two or more atoms are sharing electrons and form an electrically neutral molecule.
Ionic Bond: Electrons from one atom (e.g. Na) are transferred to another atom (e.g Cl). The resulting positively and negatively charged ions atoms attract each other strongly, forming an ionic bond. More Information on ionic bonds

bond energy

Enerrgy required to break a bond. Bond energy of :
Covalent Bonds : 50 - 110 kcal/mol (e.g. Cl - Cl : 58 kcal/mol ; H - CL : 103 kcal/mol ; C - H : 80 kcal/mol
Ionic Bonds : 4 - 8 kcal/mole
Hydrogen Bonds : 4 - 5 kcal/mol
Polar Bonds : or Dipole Dipole interactions : 2 - 3 kcal/mol
Hydrophobic Interactions : 1 kcal/mol

carbohydrates

Class of compounds with the general formula of CH₂O. They function as enery storage and structural support in living organisms.

dalton

Named after John Dalton, an english scientist. Dalton has the same meaning as atomic mass units.

condensation reaction

A chemical reaction in which water is eliminated. All biopolymers such as DNA, RNA, polysaccharides, globular proteins, fibrous proteins, cell wall components etc are formed in condensation reactions. The reaction is easily reversed by addition of water to the polymer. This is called hydrolysis. Thus the degradation of biopolymers is a hydrolysis reaction. More information.

dipole

Positive and negative charges on a molecule separated by a distance. Molecules with polar bonds and a certain shape have a dipole moment.

dissociation constant

The dissociation constant of an electrolyte such as a weak acid HA is a measure for the degree of dissociation of HA into H⁺ and A^-. The dissociation constant is expressed as the product of the concentrations of the dissociated species divided by the concentration of the undissociated species :
K_HA = [H⁺] x [A^-] / [HA]
For more information click here

electron

Electrons are negatively charged subatomic particles. The mass of an electron m_e = 9.1094x10^-28 g, which is 1/1837 of the mass of a proton or a neutron. Electrons orbit the atomic nucleus

electronegativity

The tendency of an atom to attract electrons. Click here for a more detailed explanation

element

Elements are substances which consist of the same kind of atom atoms. There are 92 different naturally occuring elements. Hydrogen with an atomic number atomic number of 1 is the lightest and uranium (atomic number 92) the heaviest.

enantiomer

see optical isomers atoms.

half live

The half life of an radioactive element is the time it takes to decay have of the original amount of the element. Click here for a more detailed explanation

hexose

A monosaccharide with 6 carbon atoms. Hexoses, such glucose, fructose, galactose and mannose are the most common monosaccharides in living organisms.

hybridization

Formation of energetically equivalent orbitals from orbitals of different energy levels. For example the 2s² and 2p² orbitals of carbon hybridize to form 4 sp³ hybrid orbitals, each containing one electron.

hydrogen bond

Directed polar interaction between a H bonded to N, O or F and a N, O or F atom. Click here for more information

hydrophobic interaction

Interaction between non polar molecules. The bond is very weak i.e it has a very low bond energy . The bond is formed through induced, transient dipole interactions

ion

Ions are atoms which have lost or gained electrons in their outer electron shell. If an atom accepts electrons anions are formed, if an atom loses electrons cations are formed. See also explanations on ionization and electronegativity

ionization

Process of removal of the outermost electron(s) from an atom. Click here for more details.

ionization energy

Energy required to remove the outermost electron from an atom.

isotope

Isotopes are atoms of the same element, differing by the number of neutrons. For example naturally occuring chlorine has two stable isotopes Cl-35 and Cl-37. The nucleus of Cl-35 has 17 protons and 18 neutrons, whereas the nucleus of Cl-37 has 17 protons and 20 neutrons.

ketose

A monosaccharide with a carbonyl function (-CO-). Dihydroxyacetone, ribulose, fructose and sorbose are ketoses

mass number

The mass number (M) of an atom is equal to the number of protons and neutrons of the atom. For example carbon-12 has 6 protons and 6 neutrons, thus, its mass number M = p + n,
M = 6 + 6 = 12. The chlorine isotope Cl-35 has 17 protons and 18 neutrons. Its mass number M_Cl-35 = 17 + 18 = 35. The Cl-37 isotope has 17 protons and 20 neutrons,
M_Cl-37 = 17 + 20 = 37.
However, the atomic weight of naturally occuring chlorine is (35 x 0.7553) + (37 x 0.2447) = 35.5 amu , where 75.53% and 24.47% are the natural abundances of the Cl-35 and Cl-37 isotopes.

monosaccharide

A monosaccharide or sugar is a carbohydrate that can not be broken down (hydrolized) into smaller sugars. Monosaccharides have between 3 and 7 carbon atoms.

neutron

A neutron is an electrically neutral subatomic particle. Its mass is m_n = 1.6749x10^-24 g. Neutrons are principal components of the atomic nucleus

nucleus

The nucleus of an atom is composed of subatomic particles with protons and neutrons as the principal components

octet rule

elements of the 1 ^rst and 7 ^th main group in the periodic system have the tendency to attain 8 electrons in their outermost shell when they form chemical bonds.

optical isomers or enantiomers

Compounds that are mirror images of each other. Optical isomers have identical chemical properties, they differ only in their interaction with polarized light. Naturally occuring amino acids have L-configuration, where as sugars have D-configuration

orbital

Orbital are specifically shaped spaces around the nucleus of an atom which can be occupied by one or two electrons. See Chemistry Review for more explanations.

pentose

A monosaccharide with 5 carbon atoms. One of the most important pentoses is ribose which is part of the structure of nucleic acids

periodic table

Arrangement of elements according to increasing atomic numbers. See Chemistry Review for a more detailed explanation

proton

A proton is a positively charged subatomic particle. Its mass is m_p = 1.6726x10^-24 g. Protons are principal components of the atomic nucleus

radioactivity

See Chemistry Review for an explanation.

radiation

See Chemistry Review for an explanation.

polysaccharide

A polymer of three or more units of monosaccharides. Important polysaccharides are starch, cellulose, glycogen and amylopectin.

spin

An electron can be viewed as spinning around its own axis in either clockwise or counter clockwise direction. Two electrons occupying the same orbital must have opposite spin.

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