NCERT 2020-2021 CLASS 10- METALS AND NON-METALS NOTES PART-2
CHEMICAL PROPERTIES OF
METALS
 |
| NCERT CLASS 10- 2020-2021-METALS AND NON-METALS- NOTES- PART-2- CHEMICAL PROPERTIES OF METALS |
You have studied earlier that on burning the magnesium ribbon, white ash is produced. Magnesium burns with a dazzling flame and when this white ash is dissolved in water and tested with red litmus paper, it turns blue in colour.
Another activity for a non-metal can be performed. Sulphur is taken in a china dish and it is heated over a Bunsen burner.
Some gas is evolved and when this gas is collected by bringing an inverted test tube and then it is dissolved in water. It is found that it turns blue litmus to red in colour.
So now we will discuss the chemical properties of metals.
What happens when metals are burnt in the air?
Different metals are taken and burned in the air and it is found that different metals react with air differently.
Some metals like sodium and potassium burn in the air without heating. When they are exposed to air they will burn and convert into oxide. There are some other metals that react on heating strongly in air and form their oxides on reacting with oxygen present in the air.
So a general equation can be written.
Metal + Oxygen → Metal oxides
We have studied in the previous chapter that copper is a reddish-brown powder. When it is heated in the air, it forms black coloured cupric oxide. So the balanced chemical equation can be written:
2 Cu + O2 → 2 CuO
Similarly aluminium on heating in the air forms aluminium oxide. Its formula is Al2O3.
Balanced a chemical equation is:
4Al + 3 O2 → 2 Al2O3
Metal oxides react with the acids and form salt and water. So metal oxides are basic oxides or behave as bases and form salt and water.
Amphoteric oxides- There are certain oxides which on dissolving in water behave as acids and bases. They show both acidic and basic nature. Some metals react with acids as well as bases and form salt and water. Such oxides are called amphoteric oxides.
These oxides not only react with the acids they also react with the bases and form salt and water. Aluminium oxide and Zinc oxide are examples.
Al2O3 reacts with hydrochloric acid and forms aluminium chloride and water.
Al2O3 + 6 HCl →2AlCl3 + 3 H2O
Aluminium oxide also reacts with a base, ie, sodium hydroxide and it forms sodium aluminate.
Al2O3 + 2 NaOH → 2 NaAlO2 + H2O
The reaction of metal oxides with water
The reaction of metal oxides with water also comes under the chemical properties of metals. Most metal oxides are insoluble in water.
Some of the metal, oxides dissolve in water and form alkalis.
Na2O + H2O → 2 NaOH
K2O + H2O → 2 KOH
Sodium, as well as potassium, react vigorously. So when these metals are exposed to the air they will catch fire. That is why both sodium and potassium metals are kept immersed in kerosene oil so that they do not come in contact with the oxygen present in the air.
To avoid accidents precaution has to be taken. These metals should not be touched with wet hands.
Metals like magnesium, aluminium, zinc and lead also continuously keep reacting with the oxygen present in the air and they get covered with a layer of their oxides. This oxide layer protects these metals from further oxidation.
Iron does not burn when heated but if the iron filings are sprinkled over the flame, it will burn. Copper does not burn. Silver and gold are the very least reactive metals. They do not react with oxygen even at high temperatures and do not form oxides.
When silver jewellery or silver articles are exposed to air for a long time, it becomes black in colour. It forms silver sulphide on reacting with hydrogen sulphide gas (H2S) present in the air.
 |
| silver sulphide coating |
Anodizing- certain metals react with the oxygen present in the air and form an oxide layer which acts as a protective layer and this property
is used for making certain cooking utensils and some decorative pieces by the
process of anodizing.
Aluminium
metal is covered by an aluminium oxide layer which prevents it from further
oxidation which prevents it from corrosion.
How
anodizing is done? By electrolysis. The aluminium utensil or any aluminium object
to be coated with an aluminium oxide layer is made anode and any other metal is
made the cathode. It is electrolyzed using dilute sulphuric acid.
Oxygen gas will be liberated at the anode which will react with aluminium and cover it with the layer of aluminium oxide which acts as a protective layer. This aluminium oxide layer can also be further dyed into different colours to make it more attractive.
Thicker is the layer of aluminium oxide, protection
will be more.
 |
| Anodized and dyed article |
What happens when metals react with water?
Some metals react with cold water and
some metals react with hot water and it has been found that some metals react
with steam.
Metals react with water to form a metal oxide and
hydrogen gas is liberated. Now, these metal oxides further react with water and
form metal hydroxides.
Metals + Water→ Metal oxide + Hydrogen
Metal oxide + Water → Metal hydroxide
So let us see which are the metals that react with cold water and how do they react.
- Some of the metals react violently with water producing a lot
amount of heat like sodium and potassium. It is a very violent reaction and this reaction
must be performed very carefully because the reaction is so much exothermic. The
hydrogen gas liberated catches fire immediately.
Calcium also reacts with cold water, but the reaction is not so violent. It forms calcium hydroxide and hydrogen gas is liberated.
- Magnesium does not react with cold water. It reacts with hot water and forms magnesium hydroxide and hydrogen gas.
- Some
metals do not react with hot water. Metals like aluminium, iron and zinc react with steam.
ACTIVITY
An activity can be performed in which these metals
will react with steam in a glass tube. The sample of the metal is taken and
glass wool soaked in water is taken at one end of a dry glass tube and it is heated
with the help of a Bunsen burner. Metal is a good conductor of heat.
Steam
will be formed which will react with the metal and the gas liberated is
collected over water and this gas is hydrogen gas. When it is tested by
bringing a burning match stick, it burns with a pop sound. So the metals
which react with the steam are aluminium, iron and zinc.
- Aluminium
reacts with steam and it forms aluminium oxide and hydrogen gas. Same way iron reacts with steam and forms ferric oxide and hydrogen gas. In the same manner, zinc also forms zinc oxide and hydrogen gas is liberated.
- Metals
like lead, copper. silver and gold do not react with water at all.
How do metals react with acids?
An activity can be performed by taking
various metals and testing them with dilute acids in the lab and seeing how these
metals react with acids. Metals like sodium and potassium react violently with
dilute acids. The reaction must be performed very carefully because it is an
exothermic reaction.
Metal
+ dilute acid → salt + hydrogen gas
As
I have told you earlier sodium reacts violently with dilute hydrochloric acid
and it forms salt sodium chloride and hydrogen gas.
2Na
+ 2HCl → 2NaCl + H2
Magnesium
reacts with HCl and forms the salt magnesium chloride and hydrogen gas.
Mg
+ 2HCl → MgCl2 + H2
Aluminium
and Zinc also reacts with HCl. Now you can write the equations yourself.
So
in this case what will be formed? Think over it and write it.
In
the case of iron, ferrous chloride and hydrogen will be formed.
Now
let us see what happens in the case of Copper. Copper is very less reactive and does not react with dilute HCl. No reaction occurs.
Write
equations of the various metals with sulphuric acid yourself in the same
manner. Various salts will be formed and hydrogen gas will be liberated.
Most
of the metals do not react with nitric acid because nitric acid is a very
strong oxidizing agent. It oxidizes the hydrogen gas liberated to water and
nitric acid itself gets reduced to the oxides of nitrogen like dinitrogen oxide
N2O nitric oxide NO and
nitrogen dioxide NO2.
So
hydrogen gas is not liberated in the case of nitric acid reacting with metals.
But
the metals like manganese and magnesium react with very dilute nitric acid and
form salt and hydrogen. So manganese on reacting with nitric acid
forms manganese nitrate and hydrogen gas and in the case of magnesium, the salt formed is magnesium nitrate.
Copper
does not react with any of the dilute acids as we have discussed earlier. Other
metals like silver, gold and lead also do not react with the dilute
acids.
Aqua
Regia is a homogeneous mixture of concentrated nitric acid and concentrated
HCl. One part concentrated nitric acid and three parts concentrated
hydrochloric acid. The ratio of 1:3.
It
can dissolve the metals like platinum and gold. These metals do not dissolve in
any of the acids but dissolve in the aqua regia.
How do metals react with the solutions of other metal salts?
For studying this property an activity can be performed by taking two test tubes. In one test-tube iron nail is taken and it is dipped in copper sulphate solution which is blue in colour.
In another test tube, a copper nail is taken and it is dipped in FeSO4 solution which is green in colour. Now keep it
aside for some hours and then observe the changes.
 |
| blue coloured CuSO4 & green coloured FeSO4 |
You
will find that in the first test tube, the iron nail surface is covered by a
reddish-brown layer and the colour of the copper sulphate solution is also
a bit faded whereas there is no change in the other test tube.
Do
you know why? You have already studied it. Think over it. Why has this
happened?
Let
us discuss a general reaction.
Metal
A + Salt solution of Metal B → Salt solution of Metal A + Metal B
Metal
A has displaced metal B from its salt solution. ie, metal A is more reactive
than metal B. We can now write the equation as follows:
Fe + CuSO4 → FeSO4 + Cu
The solution of ferrous sulphate is green in colour. So the light green colour will
be obtained and you will find that the outer surface of the iron nail has become
reddish-brown in colour due to the deposition of copper metal.
It
clearly shows that iron is more reactive than copper. A displacement reaction
has occurred.
You
have studied earlier that a more reactive metal displaces a less reactive
metal from its salt solution.
Now
in the second test tube, copper is less reactive than iron and hence no reaction will occur.
Cu
+ FeSO4 → No reaction
Another
activity is performed with a copper nail or a thin sheet of copper. It is placed
in a silver nitrate solution. Will the reaction occur? Think over it?
In
this particular case, the reaction will occur and copper nitrate will be formed
and greyish white silver will be deposited on the surface of copper. What does
it show? It shows that copper is less reactive than silver.
On
the basis of the displacement reaction, we come to know about the metals. We know about the reactivity
of the various metals based on which a reactivity series can be made.
What
is a reactivity series? It is the arrangement of metals in the decreasing order of
their reactivity. It has a major role in the study of the chemical properties of
metals.
Reactivity
series
Potassium (most
reactive)
Sodium
Calcium
Magnesium
Aluminium
Zinc
Iron
Lead
Hydrogen
Copper
Mercury
Silver
Gold (least reactive)
Potassium
is the most reactive metal and gold is the least reactive metal. At the top are
the most reactive metals and are good reducing agents and at the bottom are the
least reactive metal.
Do metals and non-metals react to each other?
We
have studied earlier the reaction of metals with various reagents and now we
will study how metals and non-metals react with each other. Why do metals and
non-metals react?
To
understand this let us study noble gases, metals and non-metals. Their
electronic configuration will tell us the reason behind the reaction of metals
and non-metals.
As
you know noble gases are unreactive and have a stable electronic configuration.
Their outermost shell is complete. All the noble gases have either two
electrons in the outermost shell-like helium or eight electrons in the
outermost shell-like neon or argon.
So
let us first of all study why noble gases are inert in nature. Noble gases do
not react because they already have a stable electronic configuration. Helium has
2 electrons in the outermost shell and this is a stable configuration.
Neon
- atomic number 10 - 10 electrons- two shells -2,8 .
It
has eight electrons in the outermost shell. This is a stable electronic
configuration. It is inert in nature.
Argon
has 18 electrons -2,8,8 .It is also inert in nature and chemically
inactive.
Now
let us study the electronic configuration of metals and non-metals.
Sodium
- atomic number -11 - 11 protons and 11 electrons. The electronic configuration is 2,8,1. The outermost shell or valence shell is not
complete. It has one electron in the outermost shell.
Magnesium
-12 electrons. -2,8,2. It has two valence electrons.
Aluminium
- 13 electrons - 2,8,3. Three valence electrons are there.
Potassium
-19 electrons - 2,8,8,1. one valence electron
Calcium
-20 electrons - 2,8,8,2. It has 2 valence electrons
So
all these metals do not have a stable electronic configuration. What do we
conclude from this? Metals react to attain inert gas configuration by losing electrons. If they lose the electrons from the outer shell to react they
will attain an inert gas configuration or stable configuration.
Let
us take the case of non-metals
Nitrogen
-7 electrons - 2,5
Oxygen
-8 electrons - 2,6
Fluorine
– 9 electrons - 2,7
Phosphorous
- 15 electrons - 2,8,5
Sulphur
-16 electrons- 2,8,6
Chlorine
– 17 electrons - 2,8,7
Nitrogen
has five electrons in the outermost shell and to attain inert gas
configuration, it needs three more electrons. Oxygen has six electrons in the
outermost shell and they need 2 more electrons for stable configuration.
Octet
means having eight electrons in the outermost shell and if there are two
electrons in the outermost shell, it is called duplet.
The same is the case with fluorine also. Has one electron less to attain octet.
So
we can arrive at the conclusion that metals and non-metals react to
complete their duplet or to complete their octet to attain inert gas
configuration or a stable configuration.
Now
let us take the case of metal sodium.
Sodium
as you have seen it has one valence electron. We can represent sodium atoms by
electron dot structure which is called the electron-dot representation of an
atom. Electron dot structure is written by writing the number of valence
electrons on the symbol in the form of dots. So one dot is made on the symbol
of sodium.
Na
x
If
sodium loses one electron it will attain an inert gas configuration. So here
it is 2,8,1. After losing one electron, it attains the configuration of noble gas and becomes Na+.
Na
→ Na⁺ + e⁻
But
by losing one electron it also gains a unit positive charge because the number
of electrons is less now and the number of protons is the same. That is
eleven electrons became ten now.
Electronic
configuration of Cl is 2,8,7. So it has seven valence electrons.
xx
x
Cl xx
xx
The
electron lost by the sodium atom is gained by chlorine and it becomes Cl⁻. Minus sign shows that the electron is
negatively charged.
xx
Na x
↗
x Cl xx
xx
Cl
+ e⁻ → Cl⁻
Chloride
ion has attained the configuration of argon(2,8,8). Sodium-ion has attained the
configuration of neon(2,8). When these oppositely charged ions come close to
each other they are attracted strongly by the electrostatic force of attraction and
they form sodium chloride.
Na⁺ +
Cl⁻ → NaCl
We
can also discuss the case of MgCl2 (magnesium
chloride). Magnesium has two valence electrons.
By
losing these two electrons it also attains inert gas configuration and becomes
stable and gains two-plus charges, whereas two chlorine atoms gain two electrons
and form two chloride ions. Mg²⁺ and two Cl⁻ attract each other and form MgCl2. These types of compounds are called ionic
compounds or electrovalent compounds.
Ionic
compounds are formed by the transfer of electrons from one atom to another.
You
can find some more ionic compounds and write down the electron dot
structure and see how they are formed. Metals will lose electrons and form
positive ions and non-metal will gain the electrons to form the negatively
charged ions.
Properties of ionic compounds
- Ionic compounds are generally crystalline solids. Generally, ionic compounds are hard and crystalline solids because oppositely charged ions are packed together with strong electrostatic forces of attraction. That is why ionic compounds are solid and they are brittle. They easily break on being hammered.
 |
| crystal salt |
To study the next property an activity can be performed. Take an ionic compound in a spatula. Heat it over the flame of Bunsen Burner.
Another property is solubility. Different ionic compounds like NaCl, KCl or MgCl2 are taken and their solubility in water and organic solvents like alcohol or ether is checked. It is found that ionic compounds are soluble in water, but are insoluble in organic solvents like alcohol and ether. Ionic compounds are insoluble in kerosene and petrol also.
It shows that when NaCl is dissolved in water, sodium ions and chloride ions separate and allow the current to pass through the solution. Sodium chloride in the solid state does not conduct the electric current. In the molten state also sodium ions and chloride ions present in it will allow the current to pass through them.
It is found that only on prolonged heating does sodium chloride melt. It has a very high melting point.
All the ionic compounds have very high melting and boiling points. The positively charged ions and negatively charged ions are held together by strong electrostatic forces of attraction and a lot of energy is required to separate them.
Moreover, the electrostatic force of attraction between the ions is overcome due to the heat. So ionic compounds are good conductors of electricity in the solution form when dissolved in water or in the molten state.
FOR PART -1 METALS AND NON-METALS-PLEASE CHECK
The chemical properties of metals is a very important topic from class 10 metals and non-metals in the examination point of view. Chemical equations from this topic are very important. You have to draw and practice the electron dot structure of the formation of different ionic compounds.
No comments:
Post a Comment