Dictionary N

Naphtha

Naphtha is a hydrocarbon, which is used as a fuel.

Natural gas is a naturally occurring mixture of gaseous hydrocarbons. The approximate composition of natural gas is 85% methane, 10% ethane, 3% propane, with lesser amounts of butane, and other higher alkanes. Natural gas is used as a fuel and for the manufacture of chemicals.

Nature of Reactants

The nature of reactants determine the course of a chemical reaction.

Negative Ions

Negative ions are atoms or groups of atoms that have acquired one or more electrons.

Neutral Oxides

Neutral oxides are those oxides, which show neither basic nor acidic properties when they react with water. Examples include carbon monoxide and nitrous oxide which are only slightly soluble in water and nitric oxide which is appreciably soluble in cold water.

Neutron

The neutron is a sub-atomic particle, which resides in the nucleus, which is the central core of the atom, and it has unit atomic mass and no charge.

Nitrates

Nitrates are the salts of nitric acid, and are strong oxidising agents.

Nitro-Glycerine

Nitro-glycerine is an oil which crystallises on cooling. The liquid is highly explosive, and detonates violently when subjected to slight shock.

Nitrogen Cycle

The nitrogen cycle involves the fixation of atmospheric nitrogen and the transport of the ammonia and nitrates so formed to the soil as nutrients for the growth of plants.

Nobel Gas

The noble gas elements, whose atoms have full outer orbitals tend to be stable, inert and not chemically active, are found in Group 0 Elements of the periodic table. The elements in this group are

Helium
Neon
Argon
Krypton
Xenon
Radon

Helium is an inert gas, because it has two electrons in its outer orbital. Only two electrons may reside in an s-orbital of helium and therefore the outer orbital is full.

The noble gases are characterised by their stable electronic configurations. The small atomic radii and high ionisation potential values suggest the presence of strongly bound electrons. There are no molecules and the inert gases are all monatomic. Low values for the boiling points indicate the presence of weak Van der Waal's Forces. Melting points and boiling points increase with atomic size.

They were called the inert gases, because it was thought that they would not react with other elements. Helium and Neon are not known to combine with other elements. However, compounds of the higher members of the noble gas group have been found, this is due to the presence of d orbitals (e.g. xenon tetrafluoride and krypton difluoride).

Helium is used along with oxygen by divers. Neon is used in neon sign electrical discharge tubes. Argon, krypton and xenon, are used in incandescent lamps. Radon a radioactive noble gas is used in the treatment of malignant growths.

Nomenclature of Alcohols

Alcohols are named by three different naming systems. The International Union of Pure and Applied Chemistry system is analogous to the ones used for alkanes and alkenes.

Systematic names for alcohols in the series are derived by applying the following rules : Select the longest continuous carbon chain carrying the hydroxyl group as the parent structure. Consider a particular alcohol to be derived from this structure by replacement of one or more hydrogen atoms by different atoms or groups of atoms. Indicate the position of the hydroxyl group in the parent structure by the lowest possible number. Indicate the position of any substituents in the parent structure by a number. Replace the terminal "e" of the appropriate alkane by the suffix "-ol". Most of the simpler alcohols are known by their common names. These names consist of the name of the alkyl group, followed by the word alcohol. For example :


          CH3CH2OH                      CH3CHCH3 
                                           OH  
          Ethyl alcohol                Isopropyl       
                                        Alcohol 

                CH3                          CH3       
           CH3CHCH2OH                     CH3COH  
                                             CH3       
          Isobutyl alcohol                tert-Butyl      
                                            Alcohol

It should be noted that similar names do not always mean the same classification. For example, isopropyl alcohol is a secondary alcohol, whereas isobutyl alcohol is a primary alcohol. Compounds which are too complicated for common names may be given derived names. According to this system, alcohols are considered to be derived from methyl alcohol, CH3OH by the replacement of one or more hydrogen atoms by other groups. The group attached to the carbon bearing the OH is named and then add the suffix carbinol to include the COH portion.

Nomenclature of Alkanes

The nomenclature rules for alkanes requires that the names of all alkanes end in "-ane". The nomenclature system agreed by International Union of Pure and Applied Chemistry, is now widely used for naming these and other classes of organic compounds and is likely to be adopted universally in due course. This system enables us to describe structures of the alkanes systematically by observing certain rules.

The longest continuous chain of saturated carbon is selected as the parent hydrocarbon and name compounds as variants of this hydrocarbon by replacing hydrogen atoms by alkyl groups.
```
                              1 2 3 4 5     
                             CH3CHCHCHCH3    
                              H3C CH3     
                         2, 3 -dimethyl pentane  
```
The compound is therefore called a pentane, and since there are two methyl substituents on the linear chain, it is a dimethylpentane.
Give each carbon atom a number so that the lowest possible numbers are used. In numbering the carbon atoms always start at that end of the chain which will result in the lowest numbers for the side chain groups. Thus, the above compound is therefore called 2, 3 -dimethyl pentane, and not 3, 4 -dimethylpentane.
Use the prefix di, tri, tetra, etc. to indicate that a substituent occurs more than once in the side chain of a compound.

When there are two identical substituents at the same carbon atom, numbers are supplied for each,


                          CH3      
                       H3CCCH2CH3     
                          CH3      
                   2-2-dimethylbutane.

Name substituents in alphabetical order.


                          CH3     
                    CH3CH2CHCHCH2CH3        
                            C2H5 
                   3-ethyl-4-methylhexane

Derivatives of the alkanes such as RBr and RNO2, where R is an alkyl group, are named as haloalkanes and nitroalkanes, respectively
```
                   CH3CH2CH2CHCH3  
                            Cl      
                   2-chloropentane 
```
CH3H2CH2CH2NO2 1-nitrobutane
Alkanes with halogen and alkyl substituents are named as haloalkylalkanes ( not alkylhaloalkanes ).
```
                      CH3       
               CH3H2CHCHCH3    
                    Br   
             3-bromo-2-methylpentane 
```
The longest chain in the above example consists of five carbon atoms.

Nomenclature of Alkenes

The nomenclature rules for alkenes requires that the names of all alkanes end in "-ene". The nomenclature system agreed by the International Union of Pure and Applied Chemistry, for the naming of the alkenes can be summarised as follows:

Select the longest continuous chain containing the carbon to carbon double bond as the parent hydrocarbon and name the compound as a derivative of this structure when hydrogen atoms have been replaced by alkyl groups. The names of alkenes all end in "-ene", (e.g. ethene, propene, butene, pentene, etc.).

Give the position of the first carbon atom attached to a C=C the lowest possible number, e.g.


                  HH H                HH HH       
                  HCCC=CH              HCC=CCH 
                  HH                  H   H     
                 But-1-ene            But-2-ene       
                  
                   H               HCH3   
                  HCC=CH          HCC=CH  
                   HH H            H  H     
                 Propene         2-Methylpropene

Nomenclature of Alkynes

The nomenclature rules for alkynes requires that the names of all alkanes end in "-yne". The nomenclature system agreed by the International Union of Pure and Applied Chemistry (IUPAC) for the naming of the alkynes can be summarised as follows:

Select the longest continuous chain containing the carbon to carbon double bond as the parent hydrocarbon and name the compound as a derivative of this structure when hydrogen atoms have been replaced by alkyl groups. The names of alkenes all end in "-yne", (e.g. ethyne, propyne, butyne, pentyne, etc.).

Give the position of the first carbon atom attached to a C C triple bond the lowest possible number, e.g.


                    HH                   H     H      
                  HCCCCH          HCCCCH  
                    HH                   H      H      
                 But-1-yne          But-2-yne

Non-Metal

Non-metal are the elements which has the physical properties of having a dull appearance, having low densities, and are poor conductors of heat and electricity. In general. non-metals react with oxygen to form acidic oxides.

Nuclear Atom

The nuclear atom was proposed by Rutherford to explain the scattering of alpha particles by gold foil, and the theory now forms the basis of our understanding of the chemical properties of the elements.

Nucleon

Nucleons are the constituents of the nucleus in an atom, and include neutrons and protons.

Nucleophile

Nucleophiles are atoms, or radicals, which are attracted to electron deficient sites in a molecule.

Nucleophilic Aromatic Substitution

Nucleophilic aromatic substitution occurs when an atom or group which is attached to an aromatic ring is replaced by another atom or group. Benzene, C6H6, is the simplest aromatic compound and is often presented as a six-member ring with alternating single and double bonds. However, these bonds exist as resonance hybrids, leading to significant stabilisation of the ring structure. Because of this stability of the aromatic ring, arenes tend to undergo substitution reactions to preserve the aromatic character of the ring, and the attacking nucleophile displaces a hydrogen atom from the ring. Therefore, the double bonds in an aromatic systems do not undergo the type of addition reactions observed for the Alkenes Alkynes.

Nucleus

The nucleus is the central core of an atom, in which the neutrons and protons reside. The nucleus contains most of the mass of an atom.

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