Non-metals

Introduction

Non-metals behave just opposite to that of metals in many ways. Physically, a nonmetal is characterized by its low melting point, boiling point, and the density. A nonmetal is typically brittle in its solid form and it exhibits a very poor thermal conductivity as well as the electrical conductivity. Chemically, nonmetals tend to show relatively high ionization energy, electron affinity, and electronegativity. They gain or share electrons when they react with a few other elements and chemical compounds. Non-metals are divided into Seventeen elements; most of them are gases (hydrogen, helium, nitrogen, oxygen, fluorine, neon, chlorine, argon, krypton, xenon and radon); one is a liquid (bromine); and a few are solids (carbon, phosphorus, sulfur, selenium, and iodine). Nonetheless, metalloids such as boron, silicon, and germanium are sometimes counted as nonmetals.

 

Physical properties of non-metals

  1. Non-metals are Non-malleable and brittle hence, they can easily break into pieces when stretched or forced with weight. For example, Sulphur and phosphorous.

  2. Non-metals are Non-ductile, therefore  we cannot craft them into thin wires as they brake into pieces when stretched

  3. Non-metals are the bad Conductors of Heat and Electricity as they do not have free electrons. Free  electrons are accountable for the transfer of heat and electricity

  4. Non-metals are non-lustrous so which cannot be polished like metals.

  5. Non-metals are available in a variety of forms, therefore,  they can be traced in solid, liquid or gaseous form within a narrow range of room temperature.

  6. Non-metals are characterised by low melting and boiling points when compared to the metals.

  7. Non-metals are not as strong as metals.

  8. Mass and density of non-metals are low, hence they are lighter.

  9. Non-metals are non-sonorous.

 

Valency of non-metals

The number of electrons accepted by a non-metal is called the Valency of a non-metal. For example, one atom of chlorine accepts 1 electron to form a negative chloride ion (Cl–), so chlorine is a non-metal. So, an atom of chlorine gains 1 electron hence, the valency of chlorine is  Cl      +    e-    → Cl–
 

Chemical properties of non-metals

Non-metals are also called electronegative elements because the non-metal atom form negatively charged ion by accepting electrons. The following are the important chemical reactions of non-metals.

1. Reaction of Non-metals with Oxygen
: All non-metals react with oxygen to form acidic or neutral oxides. For example, Carbon forms acidic carbon dioxide on reacting with oxygen.

        C      +         O2      →    CO2
 (Carbon) ( oxygen ) (Carbon Dioxide)                                                            

In the same way, Sulphur reacts with oxygen of the air to form acidic Sulphur dioxide.

       S      +            O2         →         SO2

(Sulphur  ) ( oxygen )        (Sulphur Dioxide)                

          

2. Reaction of Non-metals with Water: Non-metals do not react with water!



3. Reaction of Non-metals with Dilute Acids: Non-metals do not react with dilute acids and don’t displace hydrogen from dilute acids, because non-metals are electron acceptors. So, they cannot supply electrons to H+ ions. Therefore, they do not displace hydrogen from dilute acids.



4. Reaction of Non-metals with Chlorine: Non-metals react with chlorine to form covalent chlorides. For example,

               H2      +         Cl2         →      2HCl
 (Hydrogen)     (Chlorine)    (Hydrogen chloride)  

        

               P4      +         6Cl    →        4PCl3

 (Phosphorous)    (Chlorine)   (Phosphorous trichloride)         

           

5. Reaction of Non-metals with Hydrogen

                H2      +           S         →  H2S

      (Hydrogen)    ( sulphur)  (Phosphorous trichloride)         

           

             N2      +      3H2         →      2NH3
   (Nitrogen)     (Hydrogen)       (Ammonia)                 

 

 

Relative comparison between the metals and non-metals

Property

Metals

Non-Metals

Physical State

Metals are solid at room
temperature with the only exception for mercury and gallium they are liquids.

Non-metals generally
exist in their solids and gaseous, form except Bromine.

Melting and boiling points

Metals generally have
high m.pt and b.pt except for gallium and caesium.

Non-metals have low
m.pt and b.pt except diamond and graphite.

Density

It is generally high.

It is generally low.

Malleability and Ductility

Malleable and ductile.

Neither malleable nor
ductile.

Electrical and thermal conductivity

Good conductors of heat
and electricity.

Generally poor
conductors of heat and electricity except for graphite.

Lustre

Poses shining lustre.

Do not retain lustre
except iodine.

Sonorous sound

Give sonorous sound
when struck.

Does not produce
sonorous sound.

Hardness

Generally hard except
Na, K

Solid non-metals are
generally soft except diamond.

 

Read more

1     

Metals and non-metals

2

Alkali metals and alkaline -earth metals

3

Periodic table

4

Metallurgy

 

Questions

  1. Distinguish between metals and non-metals

  2. Explain the general characteristics of non-metals.

  3. Why are non-metals are less conductive to heat and electricity when compared to metals?

  4. Explain the chemical properties of non-metals.

  5. Explain the reaction of metals with oxygen.

 

 



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