3. METALS AND NON-METALS
Elements can be classified as metals or non-metals on the basis of their physical and chemical properties.
The easiest way to start
grouping substances is by comparing physical properties.
PHYSICAL
PROPERTIES
Metals
Metallic lustre:
- Take
samples of iron, copper, aluminium & magnesium.
- Clean
their surfaces by rubbing with sand paper.
- The
surface becomes shining. This property is called metallic lustre.
Hardness:
- Metals
are generally hard and cannot be cut with a knife.
- The
hardness varies from metal to metal.
- But
sodium metal is soft and can be cut with a knife.
Malleability:
-
It is the ability of metals to be beaten into thin
sheets.
-
Gold and silver are the most
malleable metals.
Ductility:
- It
is the ability of metals to be drawn into thin wires.
- Gold
is the most ductile metal. One gram of gold can be drawn into a wire of about 2
km length.
- Due
to malleability & ductility, metals can be given different shapes according
to our needs.
Conductor of heat:
- Clamp
an aluminium or copper wire on a stand.
- Fix
a pin to the free end of the wire using wax.
- Heat
the wire near the place where it is clamped. Heat transfers to the area of wax.
It melts wax and the pin drops. But the metal wire does not melt.
- It
shows that metals are good conductors of heat and have high melting
points.
- Silver
& copper are the best conductors of heat.
- Lead
& mercury are poor conductors of heat.
Conductor of electricity:
- Set
up an electric circuit as shown below.
- Place
a metal in the circuit between terminals A and B.
- The
bulb glows. It indicates that metals are good conductors of electricity.
- The
wires that carry current have a coating of PVC (polyvinylchloride) or a
rubber-like material. They are insulators to prevent from electric shock.
Sonority:
- It
is the ability to produce sound on striking hard surface.
- Metals
are sonorous. So they are used to make bells.
Non-metals
- There
are very few non-metals as compared to metals.
- Non-metals
include carbon, sulphur, iodine, oxygen, hydrogen, etc.
-
Non-metals
are solids or gases except bromine (a liquid).
- Only very few non-metals have some physical properties of
metals.
|
Element & Symbol |
Type of
surface |
Hardness |
Malleability |
Ductility |
Conducts
Electricity |
Sonority |
|
Graphite (C) |
Non-lustrous |
Hard |
No |
No |
Yes |
No |
|
Coal (C) |
Non-lustrous |
Hard |
No |
No |
No |
No |
|
Sulphur (S) |
Non-lustrous |
No |
No |
No |
No |
No |
|
Iodine (I) |
Lustrous |
No |
No |
No |
No |
No |
We cannot group elements
according to their physical properties alone, as there are many exceptions. E.g.
· Metals
except mercury are solids at room temperature.
· Metals
have high melting points but gallium & caesium have very low
melting points. They melt if keep on palm.
· Iodine
is a non-metal but it is lustrous.
· Carbon
is a non-metal that can exist in different forms (allotropes). E.g. Diamond
is the hardest natural substance and has very high melting and boiling point. Graphite
is a conductor of electricity.
· Alkali
metals (lithium, sodium, potassium) are so soft and can
be cut with a knife. They have low densities and low melting points.
Elements can be more
clearly classified based on their chemical properties. E.g.
a) Burn
magnesium ribbon. Collect the ashes and dissolve in water. Magnesium
hydroxide is formed.
2Mg(s) + O2(g) → 2MgO(s)
MgO(S) + H2O(l) → Mg(OH)2
(aq)
Test
this solution with red & blue litmus paper. Red litmus becomes blue. i.e.,
Mg(OH)2 is basic.
b) Burn
sulphur powder. Collect the fumes (SO2)
by placing a test tube over the burning sulphur.
Add
some water to this test tube and shake. Sulphurous acid (H2SO3)
is formed.
S(s) + O2(g)
→ SO2(g)
SO2(g)
+ H2O(l) → H2SO3 (aq)
Test
this solution with blue and red litmus paper. Blue litmus becomes red. i.e., H2SO3 is acidic.
Most non-metals produce acidic oxides when dissolve in water. Most metals, give rise to basic oxides.
Select Your Next Topic 👇
👉 Part 1: Physical Properties
👉 Part 2: Chemical Properties
👉 Part 3: How do Metals and Non-metals React?
👉 Part 4: Occurrence of Metals
👉 Part 5: Corrosion
