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 : Non-metals 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 oxides.

i) Carbon reacts with oxygen or air when burnt. The resultant is carbon oxide.

Carbon 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.

Carbon is sometimes a reducing agent when it gives up its electrons in a reaction. For example in the formation of radicals, carbon donates electrons.  

Next        Main        Previous