4. Metals and Non-metals
Learning Objectives
By the end of the lesson, you will be able to:
☑ distinguish between metals and non-metals
☑ describe the physical and chemical properties of metals and non-metals
☑ list the uses of some metals and non-metals
MINERALS AND ORES
You have learnt that all materials Here is the exact text from the image:are made up of basic substances called elements, and that elements cannot be split into simpler substances by chemical methods. There are 118 known elements. Sodium, zinc, gold, mercury, iron, lead, barium and tin (metals); and hydrogen, oxygen, carbon, sulphur, chlorine, boron, neon and radon (non-metals) are some examples.
Only certain unreactive elements are found free in nature. Others occur in combined states as minerals. A mineral is a solid inorganic substance that is found in nature. A mineral deposit that can be mined and from which an element or compound can be obtained profitably is known as an ore.
Elements can be broadly classified into two groups—metals and non-metals.
Table 4.1 Some common ores
Fig. 4.1 Some common ores
a. Bauxite (aluminium)
b. Malachite (copper)
c. Haematite (iron)
d. Galena (lead)
e. Apatite (phosphorus)
f. Quartz (silicon)
--
---
METALS
All except 20 of the known elements are metals. Most metals are reactive; they combine with other elements in nature, such as oxygen and sulphur, and occur as oxides, sulphides and carbonates. Only a few unreactive metals like gold, silver and platinum are found as free metals in the Earth's crust.
Physical Properties of Metals
Metals are solids at room temperature, except mercury, which is a liquid at room temperature (Fig. 4.2(a)).
They are generally hard and strong, with a few exceptions such as sodium and potassium, which are soft and can be easily cut with a knife (Fig. 4.2(b)).
They have a metallic lustre (shine), especially when freshly cut.
They have high melting and boiling points, with a few exceptions like sodium, potassium and mercury.
They are good conductors of heat and electricity. Silver and copper are the best conductors of electricity, followed by gold and aluminium.
Metals are sonorous. They produce a ringing sound when struck.
Most metals have high tensile strength. They can take heavy loads without breaking.
They are malleable. Metals, with exceptions like sodium and potassium, can be beaten into thin sheets and foils.
They are ductile. Metals, with exception like sodium and potassium, can be drawn into wires.
Most metals have high density. However, sodium and potassium have low density and float on water.
Fig. 4.2 Special metals
a. Mercury
b. Sodium
---
Chemical Properties of Metals
Reaction with oxygen
Metals react with oxygen under different conditions to form basic oxides. These basic oxides react with water to form bases.
Sodium and potassium react vigorously with oxygen at room temperature.
4Na + O_2 \rightarrow 2Na_2O
To prevent this oxidation, sodium and potassium are stored under kerosene.
Magnesium reacts with oxygen only when ignited. It burns with a dazzling bright flame and forms a white powder of magnesium oxide.
2Mg + O_2 \rightarrow 2MgO
Copper and iron react with oxygen only when heated to a very high temperature.
2Cu + O_2 \rightarrow 2CuO
---
---
Reaction with water
Metals react with water to form hydroxides or oxides, along with hydrogen. Different metals react at different temperatures.
Sodium, potassium, and calcium react with cold water to form hydroxides.
2Na + 2H_2O \rightarrow 2NaOH + H_2
Magnesium
Reacts with steam or hot water to form magnesium oxide.
Mg + H_2O \rightarrow MgO + H_2
Aluminium
Forms an oxide too, but this oxide forms a protective covering over the metal and prevents further reactions.
2Al + 3H_2O \rightarrow Al_2O_3 + 3H_2
Zinc
Reacts only with steam.
Zn + H_2O \rightarrow ZnO + H_2
Iron
Reacts with steam when heated strongly.
2Fe + 3H_2O \rightarrow Fe_3O_4 + 3H_2
Copper, gold, silver, and platinum do not react with water at all.
---
Activity 4.1
Teacher Demonstration
Aim: To study the reaction of metals with water.
[Caution: This activity should be demonstrated by the teacher, and students should stand away from the table.]
Materials required:
Two 200 mL beakers
Pieces of sodium and calcium
Forceps
Knife
Litmus papers
Water
Method:
1. Fill each beaker with 100 mL of water.
2. Using forceps and a knife, cut a small piece of sodium.
3. Dry it on a tissue paper and drop it into one of the beakers.
4. Repeat the same procedure with calcium.
5. Test the water in both the beakers with red and blue litmus papers.
Observations and Conclusions:
Sodium reacts vigorously and may explode. A gas is also released.
The reaction with calcium is quick, though not as vigorous as that with sodium.
In both cases, the red litmus paper turns blue, showing that the solutions are bases.
---
Reaction with dilute acids
Most metals react with dilute acids to form their salts and liberate hydrogen gas.
The reaction with reactive metals like sodium, potassium, and calcium is violent.
Magnesium, aluminium, zinc, and iron do not react violently.
Mg + 2HCl \rightarrow MgCl_2 + H_2
Copper, silver, gold, and platinum do not react with dilute acids.
---
Reaction with bases
Only some metals such as aluminium and zinc react with strong bases like sodium hydroxide to liberate hydrogen gas.
Zn + 2NaOH \rightarrow Na_2ZnO_2 + H_2
---
Activity 4.2
Aim: To study the reaction of metals with dilute hydrochloric acid.
Materials required:
Sandpaper
Six test tubes
Dilute hydrochloric acid
Strips of magnesium, zinc, iron, tin, lead, and copper
Method:
1. Clean the metal strips with sandpaper.
2. Add dilute hydrochloric acid to the six test tubes.
3. Insert a strip of metal into each test tube. Observe if any bubbles are formed in the test tubes.
If no bubbles are seen, warm them gently in a beaker of hot water.
4. Observe the speed at which gas is generated. This gives an idea of the speed of the reaction.
5. Classify the metals in order of their reactivity with dilute hydrochloric acid.
[Caution: Acids are corrosive and should be handled carefully.]
---
Activity 4.3
Aim: To study the reaction of metals with bases.
Materials required:
Small piece of zinc
Beaker
Sodium hydroxide
Method:
1. Prepare warm sodium hydroxide or caustic soda solution.
2. Drop the piece of zinc into it.
Observations and Conclusions:
You will notice that zinc reacts with sodium hydroxide to liberate hydrogen gas.
Observations on Metals with Dilute Acids
Metals like sodium, potassium, and calcium react violently with dilute acids to liberate hydrogen gas.
Magnesium, aluminium, zinc, and iron also displace hydrogen from dilute acids, but the reaction is not violent.
Metals such as copper, silver, gold, and platinum do not displace hydrogen from dilute acids.
---
Activity Series of Metals
The activity series of metals is the arrangement of metals in decreasing order of reactivity.
The series in the book shows reactivity decreasing from top to bottom.
Potassium is the most reactive metal while gold is the least reactive.
---
Displacement of a Metal by Other Metals
A more reactive metal displaces a less reactive metal from its compounds in an aqueous solution.
Some examples:
Mg + CuSO_4 \rightarrow MgSO_4 + Cu
Zn + FeSO_4 \rightarrow ZnSO_4 + Fe
Iron can displace copper from copper sulphate solution (as shown in Activity 4.4).
The solution turns green, and reddish-brown copper deposits on the iron nail.
Copper cannot displace iron from iron sulphate solution, showing that copper is less reactive than iron.
Cu + FeSO_4 \rightarrow \text{No reaction}
Question: What do you think will happen if you place a silver spoon in copper sulphate solution?
---
Activity 4.4 - Displacement Reaction
Aim: To study a displacement reaction.
Materials Required:
Test tube
Iron nail
Copper sulphate solution
Method:
1. Fill the test tube with copper sulphate solution (blue in colour).
2. Place the clean iron nail in the solution.
Observations and Conclusions:
After about an hour, the solution changes to green, and a reddish-brown deposit is formed on the iron nail.
---
Corrosion of Metals
Corrosion is the destruction or damage of a material due to chemical reaction.
Rusting of iron happens when iron is exposed to moist air, forming a reddish-brown layer of rust.
Rust is iron oxide, which eventually flakes off, damaging the object.
Definition written on the page:
"Slow eating of a metal’s surface due to oxidation is called corrosion of metals."
--Observations on Metals with Dilute Acids
Metals like sodium, potassium, and calcium react violently with dilute acids to liberate hydrogen gas.
Magnesium, aluminium, zinc, and iron also displace hydrogen from dilute acids, but the reaction is not violent.
Metals such as copper, silver, gold, and platinum do not displace hydrogen from dilute acids.
---
Activity Series of Metals
The activity series of metals is the arrangement of metals in decreasing order of reactivity.
The series in the book shows reactivity decreasing from top to bottom.
Potassium is the most reactive metal while gold is the least reactive.
---
Displacement of a Metal by Other Metals
A more reactive metal displaces a less reactive metal from its compounds in an aqueous solution.
Some examples:
Mg + CuSO_4 \rightarrow MgSO_4 + Cu
Zn + FeSO_4 \rightarrow ZnSO_4 + Fe
Iron can displace copper from copper sulphate solution (as shown in Activity 4.4).
The solution turns green, and reddish-brown copper deposits on the iron nail.
Copper cannot displace iron from iron sulphate solution, showing that copper is less reactive than iron.
Cu + FeSO_4 \rightarrow \text{No reaction}
Question: What do you think will happen if you place a silver spoon in copper sulphate solution?
---
Activity 4.4 - Displacement Reaction
Aim: To study a displacement reaction.
Materials Required:
Test tube
Iron nail
Copper sulphate solution
Method:
1. Fill the test tube with copper sulphate solution (blue in colour).
2. Place the clean iron nail in the solution.
Observations and Conclusions:
After about an hour, the solution changes to green, and a reddish-brown deposit is formed on the iron nail.
---
Corrosion of Metals
Corrosion is the destruction or damage of a material due to chemical reaction.
Rusting of iron happens when iron is exposed to moist air, forming a reddish-brown layer of rust.
Rust is iron oxide, which eventually flakes off, damaging the object.
Definition written on the page:
"Slow eating of a metal’s surface due to oxidation is called corrosion of metals."
Uses of Metals (Continued)
Aluminium
Used in high-voltage electric lines.
Alloys like duralumin and magnalium are used in aircraft and automobile bodies.
Used for making aluminium foil and cooking utensils.
Copper
Good conductor of electricity → Used in electrical wires, cables, motors, and transformers.
Good conductor of heat → Used in the bottoms of stainless steel vessels.
Zinc
Used to make corrosion-resistant galvanised iron (GI) pipes and sheets.
Used as an electrode in dry cells.
Other Metals
Gold and silver → Used in jewellery.
Lead → Used in electrodes of lead storage batteries (used in automobiles and inverters).
Chromium → Used for electroplating iron to give a shiny, corrosion-resistant finish.
---
Looking Back (True/False Statements)
1. Gold, silver, and platinum are found in the Earth’s crust as free metals. → True
2. Most metals are solids that are soft. → False
3. Metals such as zinc and magnesium react with dilute acids to liberate oxygen. → False
4. A less reactive metal displaces a more reactive metal from its aqueous solution. → False
5. The chemical name of rust is zinc oxide. → False (Rust is Fe₂O₃.xH₂O)
6. Coating zinc objects with iron is called galvanising. → False (Galvanising is coating iron with zinc)
Non-Metals
Physical Properties of Non-Metals
Exist as gases or solids at room temperature (except bromine, which is liquid).
Not as hard as metals (except diamond, which is very hard).
Low tensile strength and low density.
Low melting and boiling points (except graphite).
Not sonorous (do not produce a ringing sound).
Not malleable or ductile (cannot be beaten into sheets or drawn into wires).
Do not have lustre (except iodine and graphite).
Bad conductors of heat and electricity (except graphite, and silicon under specific conditions).
--Chemical Properties of Non-Metals
Reaction with Water
Most non-metals do not react with water.
Highly reactive non-metals (e.g., phosphorus) catch fire in air, so they are stored in water.
Fluorine, chlorine, and bromine react with water to form acids.
Reaction with Oxygen
Non-metals react with oxygen to form acidic or neutral oxides.
Carbon and sulfur react with oxygen to form acidic oxides, which dissolve in water to form acids.
Some oxides (e.g., CO, N₂O) are neutral and do not form acids.
Examples:
Carbon + Oxygen → Carbon Dioxide (CO₂)
CO₂ + Water → Carbonic Acid (H₂CO₃)
Sulfur + Oxygen → Sulfur Dioxide (SO₂)
SO₂ + Water → Sulfurous Acid (H₂SO₃)
Reaction with Acids
Unlike metals, non-metals do not replace hydrogen in acids.
Silicon reacts with hydrofluoric acid (HF).
--Uses of Non-Metals
Hydrogen
Used in the manufacture of ammonia and industrial chemicals.
Used in vanaspati (a cooking oil).
Oxygen
Used in breathing support systems in hospitals.
Used with other gases in equipment to weld metals.
Sulphur
Used in the manufacture of sulphuric acid, sulphur dioxide gas, and other industrial chemicals.
Used to make pesticides for agriculture.
Used in vulcanising rubber (making it harder) and in gunpowder.
Nitrogen
Used in the manufacture of ammonia and nitrogenous fertilisers like ammonium nitrate and ammonium sulphate.
Used as an inert gas in processed food packaging to prevent rancidity.
Silicon
Used in making semiconductors for microchips.
Silicates (oxides of silicon) are used in making glass.
Other Non-Metals
Phosphorus: Used in making fertilisers (superphosphates).
Chlorine: Used for disinfecting drinking water.
Argon: Used in welding stainless steel and filling electric bulbs.
Helium: Used in balloons for meteorological observations.
Neon: Used in fluorescent lights for advertisement displays
Flashcard (188)
Studied by 0 people
Note