Chemistry

LEARNING OBJECTIVES

After reading this  unit, you will be able to: • describe trends in reactive elements with acids, water, and halogens. • explain the trends in the physical properties across a period and down a group.

 KNOWLEDGE GAIN

Jons Jakob Berzelius was a Swedish chemist and one of the founders of modern chemistry. He proposed the first letter (or first letter and another letter) of the name of an element as its symbol.

2.1 CLASSIFICATION OF ELEMENTS

ACTIVITY 2.1: Distinguishing Metallic and Non-metallic Objects

Collect five objects made of metals. Also collect five objects made of non-metals. Compare the physical properties of metallic objects and non-metallic objects.

Observe Figure 2.1 of the periodic table. There are 118 chemical elements known at present. These elements are classified into metals, metalloids and non-metals. The metals appear at the left-hand side and middle part of the periodic table. The non-metals appear at the right-hand side of the periodic table (Figure 2.1). Metalloids lie in between metals and non-metals.

ACTIVITY 2.2: Categorizing Elements into Metals, Non-metals and Metalloids

In groups, classify all elements of periodic table into metals, metalloids and non-metals.

In the periodic table, there is a regular variation in the properties of elements in groups and periods.

2.1.1 Variation in Metallic and Non-metallic Character Across a Period

Observe Figure 2.2 (a).

In the third period of the periodic table shown in Figure 2.2(a), sodium, magnesium and aluminum are metals. The properties of silicon are in-between those of a metal and a non-metal; therefore, silicon is a metalloid. The next elements – phosphorus, Sulphur and chlorine are non-metals. The metallic character decreases from sodium to magnesium to aluminum; silicon is a metalloid; and the non-metallic character increases from phosphorus to Sulphur to chlorine. Thus, in the third period of the periodic table, sodium is the most metallic element whereas chlorine is the most non-metallic element. In general, we can say that the greatest metallic character is found in the elements on the extreme left side of a period and the greatest non-metallic character is found in the elements on the right side of a period.

On moving from left to right in a period, the metallic character of elements decreases. The non-metallic character increases on moving from left to right in a period. On the left side in a period, we have metals and on the right side we have non-metals. Some elements in-between the metals and nonmetals are known as metalloids.

EXERCISE 2.1

1. On moving from left to right in a period, the metallic character of elements ____ . 

2. How many metals are there in third period of periodic table?

3. The non-metallic character increases on moving from left to right in a period.  (True or False)

4. Choose the symbol of metalloid from the following. 

(a) Na                             (b) Si                          (c) S                    (d) Ne

Observe Figure 2.2(b). On going down in a group of the periodic table, the metallic character of elements increases. For example, when we move down in group 1 of the periodic table, the metallic character increases from lithium to francium.

                                        

Thus, in group 1 of alkali metals, lithium is the least metallic element whereas francium is the most metallic element. It is obvious that the greatest metallic character is found in the elements in the lowest part of a group.

We can also say that on going down in a group of the periodic table, the non-metallic character of elements decreases. Observe Figure 2.2(c). When we go down in group 17 of the halogen elements, the non-metallic character decreases from fluorine to iodine.  Thus, out of fluorine, chlorine, bromine and iodine, fluorine has the most non-metallic character whereas iodine has the least non-metallic character.

                                          

EXERCISE 2.2

 1. On moving down in a group of the periodic table, the non-metallic character of elements ______ .

 2. In group 17, Iodine has the least nonmetallic character. (True or False)

2.1.3 Metals

The majority of known elements (about 80%) are metals. All the metals are solid, except mercury which is a liquid metal at room temperature and pressure. Metals are elements which conduct electricity and heat. Metals are also shiny, hard and produce ringing sound when struck. Metals are widely used in our daily life for a large number of  purposes. The common metals we use are iron, copper, aluminum, tin, zinc, gold, etc. (Figure 2.3). The electric fan, machines, bicycle, cars, aero plane, cooking utensils are all made of metals or mixture of metals.

                       

During a chemical reaction, metals can form positive ions by losing electrons. Metals are the elements which form positive ions by losing electrons.

For example, sodium (Na) is a metal which forms positively charged sodium ion (Na+) by losing one electron.

Metals are very important for the national economy of every country. The economy and prosperity of a country are dependent on the natural resources produced by the country. The main metal deposits in our country are tin, coltan and tungsten.

The major metals in the earth’s crust are aluminium, iron, calcium, sodium, potassium and magnesium. Aluminium is the most abundant metal in the earth’s crust.

EXERCISE 2.3

 1. Name the liquid metal.

2. A majority of known ______ (about 80%) are metals.

3. Metals are very important for the economic growth of every country.  (True or False)

4. Which is the most abundant metal in the earth’s crust?  (a) Aluminium (b) Iron  (c) Sodium (d) Calcium

5. The main metal deposits in our country are ______ and _____.

2.1.4 Non-metals

There are only 22 non-metals. Out of these, 10 non-metals are solid, 1 non-metal is liquid and the remaining 11 are gases. Thus, all nonmetals are solids and gases, except bromine which is a liquid non-metal.

Non-metals are elements which do not conduct heat and electricity. The only exception is graphite. Non-metals are brittle, and have dull appearance. They are soft, not strong and not shiny.

          Carbon

                           

During a chemical reaction, non-metals form negative ions by gaining electrons. So we define non-metals as elements which form negative ions by accepting electrons. For example, Chlorine (Cl) is a non-metal which forms negatively charged chloride ion (Cl–) by gaining one electron.

Non-metals are small in number as compared to metals but they play an important role in our everyday life. In fact, life would not have been possible without the presence of nonmetals on earth. For example, oxygen (nonmetal) is essential for breathing to maintain life. Another non-metal carbon is one of the most important elements for existence of life on earth. This is because carbon compounds like proteins, carbohydrates, vitamins and fats are essential for growth and development of living organism. Non-metals are also used to make vegetable oil, acids, fertilisers, and fungicides.

The major non-metals in the earth’s crust are oxygen, silicon, phosphorus and sulphur. Oxygen is the most abundant non-metal in the earth’s crust. Non-metals are the major constituents of air, earth’s crust and oceans. For example, oxygen and nitrogen are the major constituents of air. Oxygen and silicon are the major constituents of earth’s crust. Oxygen and hydrogen are the major constituents of oceans.

EXERCISE 2.4

 1. Name the only non-metal which is liquid.

2. How many non-metals are found in gaseous state?

3. The only non-metal which conducts electricity is graphite. (True or False)

4. Which is the most abundant non-metal in the earth’s crust?

  (a) Carbon                (b) Oxygen                         (c) Sulphur                             (d) Nitrogen

5. Non-metals are used to make ______ and ______ .

2.1.5 Metalloids

Metalloids are the elements found along the stair-step line that distinguishes metals from non-metals. Metalloids have properties of both metals and non-metals. Some of the metalloids, such as silicon and germanium, are semiconductors. This means that they can carry an electrical charge under special conditions. This property makes metalloids useful in computers and calculators. The metalloids (Figure 2.4) are:

• Boron                                                                       • Silicon 

• Germanium                                                               • Arsenic

• Antimony                                                                   • Tellurium

 • Polonium

Metalloids tend to be economically important because of their unique conductivity properties (they only partially conduct electricity), which makes them valuable in the semiconductor and computer chip industry.

              

         EXERCISE 2.5

 1. Name two metalloids.

2. Metalloids have properties of both metals and non-metals. (True or False)

3. Silicon is used in making ______.

4. Which of the following is/are metalloid(s)?

(a) Boron (b) Germanium  (c) Antimony (d) All of these

EXERCISE 2.5

 1. Name two metalloids.

2. Metalloids have properties of both metals and non-metals. (True or False)

3. Silicon is used in making ______.

4. Which of the following is/are metalloid(s)? 

(a) Boron (b) Germanium  (c) Antimony (d) All of these

2.2 PHYSICAL PROPERTIES OF METALS

ACTIVITY 2.3: Illustrating Physical Properties of Metals

 • Collect some metallic objects.

• Note physical properties of collected objects (Get more information from internet, if available).

• Make a report on the findings.

All metals, except mercury, are solid at room temperature. For example, gold, silver, iron, copper, aluminium, etc. Metals are usually grey or silvery in color. The only exceptions are copper and gold.

Copper is reddish-brown in color whereas gold is yellow.

The other important physical properties of metals are:

1. Metals are lustrous: Metals are lustrous, that is, they have a shining surface. The shining surface of metals makes them useful in making jewelry and decorative items. For example, gold and silver are used for making jewelry.

                                      

A metal has a shining surface only when it is freshly cut. On exposure to air, metals lose their brightness due to the formation of oxide and carbonate on their surface. This is known as corrosion. If we rub the corroded metal (dull surface of metal) with sand paper, the outer corroded layer is removed and the metal object becomes shiny once again.

ACTIVITY 2.4: Illustrating the Appearance of Metals

Take samples of iron, copper, aluminium and magnesium. Note the appearance of each sample.

Clean the surface of each sample by rubbing them with sand paper and note their appearance again.

Deduction

Metals, in their pure state, have a shining surface. This property is called metallic lustre.
 

 2. Metals are hard and strong: Most of the metals are hard but all metals are not equally hard. The hardness of metals varies from metal to metal. Metals such as iron, aluminium, and copper are very hard. They cannot be cut with a knife. Sodium and potassium are soft metals. These metals can be cut easily with a knife. 

Generally metals are strong. But some metals like sodium and potassium are soft. Metals can hold large weight without breaking. For example, iron in the form of steel is very strong. Due to this, iron metal is used in machines, chains and vehicles.

ACTIVITY 2.5: Illustrating the Variation of Hardness in Metals

 • Take small pieces of iron, copper, aluminium, and magnesium. Try to cut these metals with a sharp knife and note your observations.

• Hold a piece of sodium metal with a pair of tongs.

Caution: Always handle sodium metal with care.

               Dry it by pressing between the folds of a filter paper.

               Put it on a watch glass and try to cut it with a knife.

               What do you observe?

Explanation

You will find that metals are generally hard. The hardness varies from metal to metal.

3. Metals are malleable:Metals can be beaten (hammered) into very thin sheets without breaking. This property of metals is called malleability. Gold and silver are the most malleable metals. These can be hammered into very thin sheets called foils. Aluminium foils are used for packing medicines and cigarettes.

 ACTIVITY 2.6: Illustrating the Malleability of Metals

 • Take pieces of iron, zinc, lead and copper.

• Place any one metal on a block of iron and strike it four or five times with a hammer. What do you observe?

• Repeat with other metals.

• Record the change in the shape of these metals.

Conclusion

You will find that some metals can be hammered into thin sheets. This property is called malleability.

 4. Metals are ductile: Metals are ductile.

They can be drawn into thin wires. All the metals are not equally ductile. Gold and silver are the best ductile metals. Just one gram of gold can be stretched into a wire of about 2 km  length. Copper and aluminium are also very ductile. Their wires are used in electrical wiring.

                                           

 5. Metals are good conductors of heat: Metals allow heat to pass through them easily. The conduction of heat is also known as thermal conductivity.
 

ACTIVITY 2.7: Illustrating Thermal Conductivity in Metals

Caution: Be careful while heating the objects.

• Take a steel spoon, a brass key, aluminium or copper wire (10 cm), and iron rod.

• Light the burner.

• Hold one end of iron rod in your hand.

• Keep the other end of iron rod to the flame of burner for 3 to 4 minutes as shown in figure.

                                            

 What do you feel?

• Repeat the activity with other metallic objects.

• State your observation in each case. Does the metal wire melt?

Deduction

The activity tells that metals are good conductors of heat and have high melting points. The best conductors of heat are silver and copper. Lead and mercury are comparatively poor conductors of heat.

 6. Metals are good conductors of electricity: Metals allow electricity to pass through them.

Silver metal is the best conductor of electricity, copper metal is the next best conductor of electricity followed by gold, aluminium and tungsten.

Metals are good conductors of electricity because they contain free electrons. These free electrons can move easily through the metal and conduct electric current. Thus, electrical conductivity is another characteristic property of metals. From the above discussion we conclude that metals are good conductors of heat and electricity.

Metals are good conductors of electricity because they contain free electrons. These free electrons can move easily through the metal and conduct electric current. Thus, electrical conductivity is another characteristic property of metals. From the above discussion we conclude that metals are good conductors of heat and electricity.

The electric wires that carry current in our homes have a covering of plastic such as poly vinyl chloride (PVC). Polyvinyl chloride is an insulator. It does not allow electric current to pass through it. The electric wires have a covering of an insulating material (like PVC) around them so that even if we happen to touch them, the current will not pass through our body and hence we will not get an electric shock.

ACTIVITY 2.8: Showing that a Metal Conducts Electricity

We take a dry cell, a torch bulb fitted in a holder and some connecting wires (copper wires) with crocodile clips, and connect them [as shown in Figure a] to make an electric circuit. There is a gap between the ends of the crocodile clips A and B so no current flows in the incomplete circuit shown in Figure (a) and hence the bulb does not light up. Let us now insert  (i) a piece of aluminium foil between the ends of crocodile clips A and B as shown in Figure (b) (ii) an iron rod between the ends of crocodile clips A and B as shown in Figure (b).

             

Deduction

In both cases, we see that the bulb lights up at once. This means that both aluminium foil and iron rod allow electric current to pass through them. In other words, aluminium metal is a good conductor of electricity. Note that the connecting wires used in this experiment are made of copper metal. Since these copper connecting wires allow electric current to pass through them, copper metal is also a good conductor of electricity.

 7. Metals have high melting points: Metals melt and turn into liquid at very high temperatures. However, there are some exceptions. Sodium and potassium have low melting points. Melting points of some metals are given in Table 2.1.
 

 8. Metals have high densities: The density of a substance is defined as mass of the substance per unit volume. Metals have high densities. Thus, metals are heavy substances. However, aluminium, sodium and potassium have low densities. Densities of some metals are given in Table 2.1.

                           DO YOU KNOW?

The melting point of gallium and caesium metals are so low that they start melting at temperatures  greater than 27.76°C.

      

9. Metals are sonorous: Metals are sonorous means that they are capable of producing a ringing sound. The property of metals of being sonorous is called sonority. It is due to the property of sonority, metals are used for making bells and wires of violin.

                              

EXERCISE 2.6
 1. Which metal is yellow in color?

2. Write two uses of metals.

3. Define malleability.

4. Why metals are good conductors of electricity?

5. Metals have high

  (a) melting points    (b) densities      (c) both (a) and (b)             (d) None of these.

2.3 PHYSICAL PROPERTIES OF NON-METALS

ACTIVITY 2.9: Showing that a Non-metal does not Conduct Electricity

We take a dry cell, a torch bulb fitted in a holder and some connecting wires (copper wires) with crocodile clips, and connect them as shown in Figure (a) to make an electric circuit. There is a gap between the ends of crocodile clips A and B so no current flows in the open circuit shown in figure (a).

Let us now insert

(i)  a piece of sulphur (which is a non-metal) between the crocodile clips A and B as shown in figure (b)

(ii) a carbon rod between the crocodile clips A and B as shown in figure (b).

          
         

Explanation

In both cases, we see that the bulbs do not light up at all. This means that both sulphur and carbon do not allow electric current to pass through them and no current flows in the circuit. This activity shows that non-metals do not conduct electricity.

Non-metals exist in all three physical states: solid, liquid and gaseous. For example, carbon, sulphur and phosphorus are solid. Bromine is a liquid. Oxygen, hydrogen and nitrogen are gases. Non-metals have many different colors.

For example, phosphorus is red, black and white. Sulphur is yellow, chlorine is green.

Some non-metals such as oxygen and hydrogen are colorless.

The other important physical properties of non-metals are:

1. Non-metals are not lustrous: Nonmetals do not have a shining surface. The only non-metals having a shining surface is iodine.

2. Non-metals are neither hard nor strong: Most of the solid non-metals are soft, they can be broken easily. For example, sulphur and phosphorus. Only one non-metal carbon in the form of diamond is very hard. Diamond is the hardest substance known on earth.

3. Non-metals are neither malleable nor ductile: Non-metals are brittle which means that they break into pieces when hammered or stretched. 

Therefore, non-metals cannot be hammered with a hammer to form thin sheets. They cannot be stretched to form wires. 

The property of breaking easily is called brittleness. Brittleness is the characteristic property of non-metals. Note: Brittleness is not applicable to liquid and gaseous non-metals.

4. Non-metals do not conduct heat and electricity: Non-metals do not conduct heat and electricity because they have no free electrons which are necessary to conduct heat and electricity. However, there is one exception. Carbon in the form of graphite is a good conductor of electricity. Therefore, graphite is used for making electrodes.

ACTIVITY 2.10: Illustrating Thermal Conductivity in Nonmetals

Repeat Activity 2.7 with carbon rod (taken out from used cell) and a lump of sulphur.

Activity 2.9 shows that non-metals do not conduct electricity. 

In Activity 2.10, you will observe that both carbon and sulphur are poor conductors of heat

 5. Non-metals have low melting and boiling points: Non-metals have comparatively low melting and boiling points. Only one non-metal diamond (allotropic form of carbon) has high melting point. The melting point of diamond is 3500°C.

6. Non-metals have low density: The density of non-metals is low, that is, they are light substances.  Densities of some non-metals are given in Table 2.2.

                                 

 7. Non-metals are non-sonorous: Nonmetals do not produce ringing sound when hit with an object.

EXERCISE 2.7

 1. Non-metals exist in all three physical states. (True or False)

2. ______ and ______ are colorless nonmetals.

3. Which non-metal is used for making electrodes?

4. Why do non-metals not conduct heat and electricity?

5. Non-metals have low  (a) densities  (b) melting points  (c) boiling points  (d) All of these.

2.4 TRENDS IN REACTIVITY FOR METALS AND NON-METALS

2.4.1 Reactivity of Metals

The chemical reactivity of metals increases on going down in a group of the periodic table. For example, in group 1 of alkali metals, the chemical reactivity increases from lithium to francium (radioactive).

                                     

Thus, as we go down in a group of metals, the tendency of their atoms to lose electrons increases, and hence their chemical reactivity also increases.

On moving from left to right in a period, the chemical reactivity of elements first decreases and then increases.

                                          

In the third period of elements shown above, sodium is a very reactive element, magnesium is less reactive, whereas aluminium is still less reactive. Silicon is the chemically least reactive element in the third period. Now, phosphorus is quite reactive, sulphur is still more reactive, whereas chlorine is very reactive. From this discussion we conclude that in the third period of the periodic table, chemical reactivity first decreases from sodium to silicon and then increases from phosphorus to chlorine.

                                         

2.4.2 Reactivity of Non-metals

The chemical reactivity of non-metals decreases on going down in a group of the periodic table. For example, in group 17 of halogen elements (which are non-metals), the chemical reactivity decreases from fluorine to iodine.

Thus, as we go down in a group of non-metals, the tendency of their atoms to gain electrons decreases, due to which their reactivity also decreases.

EXERCISE 2.8 1.

1.Explain, why chemical reactivity of metals increases on going down in a group of periodic table?

2. Which of the following element is least reactive? 

(a) Sodium (b) Silicon (c) Sulphur (d) Chlorine

3. The chemical reactivity of non-metals decreases on going down in a group of periodic table. Why?

4. In the third period of elements shown below Na Mg Al Si P S Cl  Sodium reacts vigorously but sulphur reacts less vigorously with oxygen.  

                                                                                 (True or False)

2.5 CHEMICAL PROPERTIES OF METALS

2.5.1 Reaction of Metals with Water

ACTIVITY 2.11: Illustrating Reaction of Metals with Water
Caution: Do not touch sodium and potassium with bare hands. They cause severe burns.

• Collect samples of sodium, potassium, calcium, aluminium, iron, magnesium, zinc and copper.

• Put small pieces of samples separately in beakers half filled with cold water.

• Observe which metals reacted with cold water.

Did any metal produce fire in water?

Did any metal start floating after sometime?

• Put the metals that do not react with cold water in beakers filled with hot water.

• Observe which metals reacted with hot water.

• For those metals which did not react with hot water arrange the apparatus as shown in figure.

                         

• Observe which metals react with steam.

Did any metal not react even with steam?

• Make an appropriate report on reaction of metals with water.

In Activity 2.11, you have observed that all metals are not equally reactive. Metals react with water to form a metal hydroxide and hydrogen gas. Some metals react with cold water. For example, sodium, potassium and calcium. Some other metals such as magnesium react with hot water. It does not react with cold water. Metals such as aluminium, iron and zinc do not react with either cold or hot water. They react with steama to form metal oxide and hydrogen. There are some metals that do not react even with steam. For example, copper, gold, silver and mercury. When a metal reacts with cold water or hot water, the products formed are metal hydroxide and hydrogen gas.

                           

a Steam is a gaseous form of water. It is very hot.

When metals such as magnesium, aluminium, zinc and iron react with steam, the products formed are metal oxide and hydrogen gas.
Metal + Steam → Metal oxide + Hydrogen
Note: Metal oxides are basic in nature. Their solutions in water turn red litmus into blue. Some metal oxides react with water to form alkali.

Example 1 Sodium reacts vigorously with cold water to form sodium hydroxide and hydrogen gas.

The reaction of sodium metal with water is also highly exothermic (heat producing). This is the reason why hydrogen gas formed during the reaction catches fire and burns causing little explosions. Thus, sodium is a very reactive metal.

Example 2 Potassium reacts violently with cold water to form potassium hydroxide and hydrogen gas.

The reaction of potassium metal with water is highly exothermic (heat producing). This is the reason why hydrogen gas formed during the reaction catches fire immediately. Thus, potassium is also a very reactive metal.

Note: Potassium is more reactive than sodium.

Example 3

Calcium reacts with cold water to form calcium hydroxide and hydrogen gas.

The reaction of calcium with water is less violent. The heat produced is not sufficient for the hydrogen to catch fire. Calcium starts floating in water because bubbles of hydrogen formed during the reaction stick to surface of metal.

                              

Note: Calcium is less reactive than sodium.

Example 4

Magnesium metal does not react with cold water. It reacts with both hot water and steam. Magnesium reacts with hot water to form magnesium hydroxide and water.

                                

In this reaction, the piece of magnesium metal starts floating on water due to the bubbles of hydrogen gas sticking to its surface.

Note: Calcium reacts with cold water but magnesium reacts only with hot water. This shows that magnesium is less reactive than calcium.
Magnesium reacts very rapidly with steam to form magnesium oxide and hydrogen.

                                       

When magnesium reacts with hot water, it forms magnesium hydroxide and hydrogen. In this reaction, magnesium reacts with steam to form magnesium oxide and hydrogen.

Example 5 (i) Aluminium reacts with steam to form aluminium oxide and hydrogen gas.

                                       

 (ii) Zinc reacts with steam to form zinc oxide and hydrogen gas.

                                     
 (iii) Iron reacts with steam to form iron oxide and hydrogen gas.

                                    
Example 6

Copper does not react with water (or steam)

                                        

2.5.2 Reaction of Metals with Acids

ACTIVITY 2.12: Illustrating Reaction of Metals with Dilute Acids

Caution: Do not touch dilute hydrochloric and sulphuric acids with your bare hands.

• Collect small pieces of magnesium, aluminium, zinc, copper and iron.

• Clean the sample metals with sand paper.

• Put these metal pieces in separate test tubes.

• Add 10 ml dilute hydrochloric acid to each test tube.

• Observe carefully the rate of formation of hydrogen gas bubbles. Did any metal not react with dilute hydrochloric acid?

• Repeat the activity again with dilute sulphuric acid. Did any metal not react with dilute sulphuric acid?

• Make an appropriate report on reaction of metals with dilute acids.

In Activity 2.12, you must have observed that the rate of formation of hydrogen bubbles was the fastest in magnesium. The reactivity decreases in the order Mg > Al > Zn > Fe. In case of copper, no bubbles were seen. This shows that copper does not react with dilute hydrochloric acid.

Metals usually react with dilute acids to give a metal salt and hydrogen gas. Some metals react violently (explosively) with dilute acids whereas some react rapidly. Sodium reacts violently with dilute acids and magnesium reacts rapidly. Some metals react slowly with dilute acids whereas a few metals do not react with acids at all. Aluminium, iron, zinc and copper react slowly with dilute acids; whereas gold and silver do not react at all.

                                              DO YOU KNOW?

Aqua regia, (Latin for ‘royal water’) is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio 3 : 1. It can dissolve gold, even though neither of these acids can do so alone. Aqua regia is a highly corrosive, fuming liquid. It is one of the few reagents that is able to dissolve gold and platinum.

When a metal reacts with dilute hydrochloric acid, the products formed are metal chlorides and hydrogen gas.

                          

When a metal reacts with dilute sulphuric acid, the products formed are metal sulphate and hydrogen.

                         

Example 1

(i) Sodium metal reacts violently with dilute hydrochloric acid to give sodium chloride and hydrogen gas

                                     

 (ii) Sodium metal reacts with dilute sulphuric acid to give sodium sulphate and hydrogen gas.

                                     

Example 2

(i) Magnesium reacts with dilute hydrochloric acid to give magnesium chloride and hydrogen gas.

                                        

 (ii) Magnesium reacts with dilute sulphuric acid to form magnesium sulphate and hydrogen gas.

                                            

Example 3

(i) Calcium reacts with dilute hydrochloric acid to form calcium chloride and hydrogen gas.

                                                  

 (ii) Calcium reacts with dilute sulphuric acid to give calcium sulphate and hydrogen gas.

                                                       

Example 4

(i) Aluminium reacts with dilute hydrochloric acid to give aluminium chloride and hydrogen gas

                                                        

(ii) Aluminium reacts with dilute sulphuric acid to form aluminium sulphate and hydrogen gas.

                                                      

Example 5

(i) Zinc reacts with dilute hydrochloric acid to form zinc chloride and hydrogen gas.

                                                     

 (ii) Zinc metal reacts with dilute sulphuric acid to give zinc sulphate and hydrogen gas.

                                               

Example 6

(i) Iron reacts slowly with cold dilute hydrochloric acid to form iron chloride and hydrogen gas.

                                                   

 (ii) Iron reacts with sulphuric acid (dilute) to give iron sulphate and hydrogen gas.

                                               

Example 7

(i) Copper does not react with dilute hydrochloric acid.

                                                   Cu(s) + HCl(aq) → No reaction

(ii) Copper does not react with dilute sulphuric acid.

                                        

Hydrogen gas is not evolved when a metal (e.g., Cu) reacts with nitric acid (HNO₃).

It is because nitric acid is a strong oxidising agent. It oxidises the hydrogen produced to water and nitric acid itself is reduced to any of the nitrogen oxides. The examples of nitrogen oxide are nitrogen monoxide (NO), nitrogen dioxide  and dinitrogen monoxide.Only magnesium and manganese react with very dilute nitric acid to evolve hydrogen gas. The reaction of magnesium and manganese metals with very dilute nitric acid are:

• Magnesium reacts with very dilute nitric acid to form magnesium nitrate and hydrogen gas

                                         

• Manganese reacts with very dilute nitric acid to form manganese nitrate and hydrogen gas.

                                             

2.5.3 Reaction of Metals with Halogens

The elements of group 17 in the periodic table are called halogens. Fluorine (F), Chlorine (Cl), bromine (Br), Iodine (I) and Astatine (At) are halogens.

Metals react with halogens to form ionic halide.

Metal halides are usually solid and conduct electricity in solution. Let us see some equations for reaction of metals with chlorine.

(i) Sodium reacts with chlorine to form sodium chloride

                                                  

 (ii) Calcium reacts with chlorine to form calcium chloride

                                                    

 (iii) Aluminium reacts with chlorine to form aluminium chloride.

                                                         

 (iv) Iron reacts with chlorine to form iron chloride.

                                                       

 (v) Copper reacts with chlorine to form copper chloride.

                                                       

 (vi) Zinc reacts with chlorine to form zinc chloride.

                                                         

Note: All the metal chlorides are ionic compounds.

2.5.4 Reaction of Metals with Oxygen

ACTIVITY 2.13: Illustrating Reaction of Metals with Oxygen

Safety: The activity needs the teacher’s assistance. Students should wear eye protection.

Collect small pieces of potassium, sodium, magnesium, aluminium, zinc, copper and iron. Also collect some iron filings.

• Hold any of the samples taken above with a pair of tongs and try burning over a flame. Repeat with other metal samples.

• Collect the product if formed.

• Let the products and the metal surface cool down. Which metals burn easily? How does the metal surface appear after burning? Are the products soluble in water?

• Make an appropriate report on reaction of metals with oxygen.

You will observe in Activity 2.13 that almost all metals combine with oxygen to form metal oxides, but all metals do not react with oxygen at the same rate. Different metals show different reactivity towards oxygen.

Metals such as potassium and sodium react so vigorously that they catch fire if kept in the open. Hence, to protect them and to prevent accidental fires, they are kept immersed in kerosene oil. At ordinary temperature, the surfaces of metals such as magnesium, aluminium, zinc, lead, etc., are covered with a thin layer of oxide. The protective oxide layer prevents the metal from further oxidation. Iron does not burn on heating but iron filings burn vigorously when sprinkled in the flame of the burner. Copper does not burn, but the hot metal is coated with a black colored layer of copper(II) oxide. Silver and gold do not react with oxygen even at high temperatures.

Let us see some equations for reaction of metals with oxygen.

 (i) Sodium reacts with oxygen to form sodium oxide.

                                         

 (ii) Potassium reacts with oxygen to form potassium oxide.

                                          

 (iii) Magnesium reacts with oxygen to form magnesium oxide

                                          

EXERCISE 2.9

 1. ______ is a gaseous form of water.

2. Metals react with water to form metal oxide and hydrogen gas.  (True or False)

3. Metals react with steam to form metal hydroxide and hydrogen gas.  (True or False)

4. Complete and balance the following equations:

                                      

 5. Gold and Silver ______ react with dilute acids.

6. Hydrogen gas is not evolved when a metal reacts with ______ .

7. All metal chlorides are ionic in nature. (True or False)

2.6 CHEMICAL PROPERTIES OF NON-METALS

Non-metals neither react with water nor with dilute acids. In other words, non-metals do not displace hydrogen gas from acids and water.

2.6.1  Reaction of Non-metals with Halogen (Chlorine)

Non-metals react with chlorine to form covalent chlorides. Non-metal chlorides are usually liquids or gases. They do not conduct electricity.

Example 1

              


2.6.2  Reaction of Non-metals with Oxygen

Non-metals react with oxygen to form acidic oxides or neutral oxides.

 (i) Carbon reacts with oxygen to form carbon dioxide

                 

 (ii) Hydrogen reacts with oxygen to form water.
                       
EXERCISE 2.10

 1. Non-metals do not displace hydrogen gas from acids. (True or False)

2. Non-metals react with ______ to form covalent chlorides.

3. Non-metals react with oxygen to form 

(a) acidic oxides              (b) neutral oxides            (c) both (a) and (b)             (d) none of these

4. Complete the following equations:

             

 5. Non-metal chlorides do not conduct electricity. (True or False)

2.7 COMPARISON AMONG THE PHYSICAL AND CHEMICAL PROPERTIES OF METALS AND NON-METALS

We have studied the physical and chemical properties of metals and non-metals. Let us see the main points of difference between the metals and non-metals.

          

           

             2.8 USES OF METALS AND NON-METALS

               

EXERCISE 2.11

 1. State True or False 

(a) Mercury is used in thermometers. 

(b) Gold and Silver are used for making electric wires. 

(c) Helium is used in balloons. 

(d) Phosphorus is used in fertilizers. 

(e) Chlorine is not used in the disinfection of drinking water.

2. Gap filling: 

(a) Sulphur is used for making ______. 

(b) Silicon is used for making ______. 

(c) Sodium is used in ______ reactors.

3. Name the Noble gas used in electric bulbs.

4. Which element is used for coating iron containers for packaging food?

5. Name two metals used for making machines.

2.9 SUMMARY

• Elements can be classified as metals, metalloids and non-metals.

• On moving from left to right in a period, the metallic character of elements decreases whereas non-metallic character increases.

• On going down in a group of the periodic table, the metallic character of elements increases whereas non-metallic character decreases.

• Metals are lustrous, malleable, ductile and good conductors of heat and electricity. They are solids at room temperature, except mercury which is a liquid.

• Non-metals have properties opposite to that of metals. They are neither malleable nor ductile. They are bad conductors of heat and electricity, except for graphite, which conducts electricity.

• Metals form positive ions by losing electrons.

• Non-metals form negative ions by accepting electrons.

• Elements in-between the metals and non-metals are known as metalloids.

• The chemical reactivity of metals increases on going down in a group of the periodic table.

• The chemical reactivity of non-metals decreases on going down in a group of the periodic table.

• Metals react with water to form metal hydroxide or metal oxide and hydrogen gas.

• Metals usually react with dilute acids to give a metal salt and hydrogen gas.

            Metal + Hydrochloric acid → Metal chloride + Hydrogen  

            Metal + Sulphuric acid → Metal sulphate + Hydrogen.

 • Copper does not react with dilute acids.

• Metals react with halogen to give ionic halides.

• Metals react with oxygen to form metal oxides (basic oxides).

• Different metals have different reactivities with water and dilute acids.

• Arrangement of common metals in order of their decreasing reactivity is known as an activity series.

• Metals above hydrogen in the Activity series can displace hydrogen from dilute acids.

• A more reactive metal displaces a less reactive metal from its salt solution.

• Non-metals neither react with water nor with dilute acids. They do not displace hydrogen gas from water and acids.

• Non-metals react with chlorine to form covalent chlorides

. • Non-metals react with oxygen to give acidic oxides or neutral oxides.

2.10 GLOSSARY

• Antiseptic: a substance that prevents the growth of disease-causing micro-organisms.

• Carbohydrates: a large group of organic compounds occurring in foods including sugars, starch, and cellulose.

• Fertilizers: a chemical or natural substance added to soil or land to increase its fertility.

• Fluorescent: emitting light.

• Fungicides: a chemical that destroys fungus.

• Metal: a material that is hard, opaque, shiny and has good electrical and heating conductivity.

• Metalloid: a chemical element with properties in between those of metals and nonmetals.

• Non-metal: a material that does not have properties of metals.

• Nuclear reactor: a device used at nuclear power plants for electricity generation.

• Ornaments: a thing used or serving to make something look more attractive.

• Thermometer: an instrument for measuring temperature.

• Weapon: something designed or used for inflicting physical injury or damage.

2.11 UNIT ASSESSMENT

I. Multiple Choice Questions

1. Which of the following metal exists in the liquid state? 

(a) Sodium        (b) Silver          (c) Mercury              (d) Neon

2. On going down in a group of the periodic table, the metallic character of
 elements .................. 

(a) increases             (b) decreases             (c) both (a) and (b)                 (d) neither (a) nor (b)

 3. Silicon and germanium are examples of .................. 

(a) metals (b) metalloids (c) non-metals (d) none of these

4. All non-metals are solids and gases except: 

(a) fluorine (b) chlorine (c) bromine (d) iodine

5. Which metal is the best conductor of electricity? 

(a) Silver (b) Copper (c) Aluminium (d) Iron

6. Which of the following statement(s) is/are not correct. 

(a) The hardest substance known on earth is diamond.  (b) Graphite – a non-metal – conducts electricity.  (c) The melting points of gallium and caesium are very high.  (d) Brittleness is the characteristic property of non-metal.

7. On moving from left to right in a period, the chemical reactivity of elements .................. 

  (a) increases   (b) decreases  (c) first decreases and then increases (d)  first increases and then decreases

8. Name the gas produced when metals react with dilute acids.

  (a) Oxygen (b) Hydrogen (c) Nitrogen (d) Chlorine

9. The molecular formula of manganese nitrate is 

     

10. Carbon reacts with oxygen to give 

(a)  carbon dioxide   (b) carbon monoxide  (c) both (a) and (b)   (d) none of these

II. Open Ended Questions

1. What is meant by saying that the metals are malleable and ductile? Explain with examples.

2. With the help of example, describe how metals differ from non-metals.

3. Name one metal and one non-metal which exist in liquid state at room temperature.

4. (a) Name the most abundant metal in the earth’s crust. 

    (b) Name the most abundant non-metal in the earth’s crust. 

    (c) Name one metal which has low melting point. 

    (d) Name one non-metal which is kept under water. 

    (e) Name one metal which is stored in kerosene oil.

5. Complete and balance the following equations:
       

                                  
 6. Describe the trends and patterns in the properties of elements in groups and periods.

 7. Illustrate electrical conductivity of metals and non-metals.

8. Distinguish between the chemical properties of metals and non-metals.

9. Can you explain why copper does not react with water?

10. Give three uses of non-metals in daily life.

III. Practical-based Questions

1. Which of the following is an example of non-metals?

                   
 

 2. Which is the most reactive metal in the given table?

                     

                    (a) Li                   (b) Na                        (c) K                   (d) Rb

3. Which is the least reactive metal in the given table?

                   

                   (a)  Na               (b) Cl                      (c) Si                         (d) P

4. How many non-metals are there in the following figure?

                                    

              (a) Five          (b) Eleven              (c) Six (                 d) Seven

 5. In the following periodic table, the yellow color represents ......................

     
           (a) Metals                   (b) Non-metals                (c) Metalloids                   (d) Liquid metals