Metals and Non-Metals - Part VI
Non-Metals display the following chemical properties :
Non-metals are less reactive than metals. They react with oxygen and salts solutions, but they do not react with water or dilute acids. In the ensuing discussions we will study these reactions. These reactions will give us some idea about chemical reactivity of non-metals.
1. Non-metals are electronegative
Atoms of non-metal elements have 1 to 4 electrons less in the outermost
shells. The atoms can therefore accept electrons while forming compounds.
The non-metal atoms therefore become electronegative in a reaction. For
example, Cl atom easily takes one electron in the M-shell to become Cl-.
2. Reaction with oxygen
react with oxygen to form non-metal oxides. Non-metal oxides are acidic or
neutral in nature. Carbon forms carbon dioxide (CO2) which is an
acidic oxide. Sulphur forms sulphur dioxide (SO2). This is also
acidic in nature. Hydrogen form di-hydrogen oxide (H2O), which is
neutral in nature. Acidic
oxides dissolve in water to produce acids. Non-metal oxide bonds are
covalent bonds. Non-metal atoms
share electrons with oxygen atoms while forming the non-metal oxide. All non-metals have to be burnt is air or oxygen to form the subsequent non-metal
i) Carbon reacts with oxygen or air when burnt. The resultant is carbon oxide.
dioxide or CO2 is an acidic oxide and when dissolved in water
becomes H2CO3 or carbonic acid.
ii) Sulphur has to be burnt in the air or oxygen to give sulphur dioxide.
Sulphur dioxide or SO2 is acidic in nature and when dissolved in water forms H2SO3 or sulphurous acid.
iii) Phosphorus is another non-metal, which has to be burnt in air or oxygen to give phosphorous pentaoxide.
Phosphorus pentadioxide or P2O5 is acidic in nature and when dissolved in water forms H3PO4 or phosphoric acid.
All the non-metal oxides discussed above are acidic in nature. When non-metals burn in air with insufficient supply of oxygen, different non-metal oxides are formed. These oxides are neutral in nature. Examples of neutral non-metal oxides are CO, H2O, NO or N2O. Some examples are shown below.
i) Carbon (C) burns to give carbon mono-oxide (CO) when there is insufficient supply of oxygen.
ii) Hydrogen is a non-metal at ordinary temperatures. When hydrogen combines with oxygen the reaction is:
3. Non-Metal reaction with water
: All non-metals do not react with
water to form either metal oxides or metal hydroxides. Whether the water is
in the form of cold water, hot water or steam, all non-metals remain
unresponsive to water. The reason for this is the typical electronic
configuration of non-metals. Non-metals are electronegative are unable to
break the bond between H and O in water. The non-metals cannot reduce
hydrogen by donating electrons.
4. Non-Metal reaction with dilute acids
: Most non-metals do not react with dilute acids. They are
not capable of replacing hydrogen from the acids and forming a salt. For
example C, S or P do not react with HCl or H2SO4 to
give off hydrogen. The reason
for this as discussed above. To release H+ from the acid, the
non-metal has to provide the extra electron. Non-metals themselves are
acceptors of electrons. Hence they are unable to displace H+ from
the acid to form a salt and release hydrogen gas. Thus when non-metals like
C, S, P are added to a test tube containing dilute acids, there will be no
reaction or evolution of hydrogen gas.
5. Non-Metal reactions with salt solutions : Reactivity of non-metals determine which salt is formed when a non-metal is added to a salt solution. More reactive non-metal displaces the less reactive non-metal in the metal salt. Example below will show a typical example.
This is a displacements reaction. A more reactive non-metal like chlorine (Cl) is displacing a less reactive non-metal bromine (Br) to form sodium chloride from sodium bromide.
6. Non-Metal reactions with chloride : Non-metals react with chlorine (Cl) to form chlorides. These are covalent compounds and are non electrolytes when in solution. Some of the reactions are shown below.
Sometimes P forms phosphorous pentachloride PCl5. Carbon forms carbon-tetrachloride (CCl4) when reacted with chloride. CCl4 is a covalent compound.
7. Non-Metal reactions with hydrogen : Non-metals react with hydrogen to form hydrides. These are covalent compounds unlike the metal-hydrides. The reactions are shown below.
Oxygen combines with hydrogen to give a neutral non-metal hydride called water!! Similarly other common non-metal hydrides are methane (CH4) and hydrochloric acid (HCl). Non-metal hydrides are generally liquids or gases and because of their covalent nature, they do not conduct electricity.
8. Non-Metals as oxidizing agents : Other than carbon, all non-metals accept electrons. Therefore they are oxidizing agents, they extract electrons from the neighboring elements. Chlorine is an oxidizing agent because it accepts an electron in its outermost orbit. It is interesting to note that even though chlorine is an oxidizing agent, it itself is getting reduced into becoming a chlorine ion.
is sometimes a reducing agent when it gives up its electrons in a reaction.
For example in the formation of radicals, carbon donates electrons.