Selina Textbook Solutions: Language of Chemistry | Chemistry Class 8 ICSE PDF Download

 Page 1


Points to Remember: 
• The valency of an element is the number of electrons donated or accepted by its 
‘atom’ during chemical combination. 
• There are some elements with more than one valency e.g., iron, copper, tin, lead. 
• Two or more different non-metals that collectively accept or donate one or more 
electrons and become negatively or positively charged in the process are 
called radicals. 
• A chemical reaction involves the transformation of original substance into an 
altogether new substance(s). 
• A chemical reaction can be represented with the help of the symbols or the 
formulae of the elements and the compounds taking part in that reaction. This 
gives a chemical equation. 
• Certain necessary conditions for a chemical reaction to happen are — close 
contact, solution form, heat, light and catalyst. 
• Characteristics of chemical reactions are — change of colour, evolution of a gas, 
formation of a precipitate, change of state, change of smell and 
evolution/absorption of heat. 
• A complete chemical equation symbolically represents the reactants, products and 
their physical states. 
• The substances that react with each other are called reactants and they are 
represented on the left hand side of the equation. The substances that are formed 
as a result of the reaction are called products. They are represented on the right 
hand side of the equation. 
• A chemical equation needs to be balanced to make it follow the law of the 
conservation of mass. 
• The law of conservation of mass states that mass can be neither created nor 
destroyed, it can only be transformed from one form to another. 
• A chemical equation gives both qualitative and quantitative information about the 
reactants and products. 
Language of Chemistry 
Page 2


Points to Remember: 
• The valency of an element is the number of electrons donated or accepted by its 
‘atom’ during chemical combination. 
• There are some elements with more than one valency e.g., iron, copper, tin, lead. 
• Two or more different non-metals that collectively accept or donate one or more 
electrons and become negatively or positively charged in the process are 
called radicals. 
• A chemical reaction involves the transformation of original substance into an 
altogether new substance(s). 
• A chemical reaction can be represented with the help of the symbols or the 
formulae of the elements and the compounds taking part in that reaction. This 
gives a chemical equation. 
• Certain necessary conditions for a chemical reaction to happen are — close 
contact, solution form, heat, light and catalyst. 
• Characteristics of chemical reactions are — change of colour, evolution of a gas, 
formation of a precipitate, change of state, change of smell and 
evolution/absorption of heat. 
• A complete chemical equation symbolically represents the reactants, products and 
their physical states. 
• The substances that react with each other are called reactants and they are 
represented on the left hand side of the equation. The substances that are formed 
as a result of the reaction are called products. They are represented on the right 
hand side of the equation. 
• A chemical equation needs to be balanced to make it follow the law of the 
conservation of mass. 
• The law of conservation of mass states that mass can be neither created nor 
destroyed, it can only be transformed from one form to another. 
• A chemical equation gives both qualitative and quantitative information about the 
reactants and products. 
Language of Chemistry 
ACTIVITY 1 
Write the names and symbols of the first twenty elements that you have studied 
in class VI & VII. 
Answer: 
 
 
 
 
Page 3


Points to Remember: 
• The valency of an element is the number of electrons donated or accepted by its 
‘atom’ during chemical combination. 
• There are some elements with more than one valency e.g., iron, copper, tin, lead. 
• Two or more different non-metals that collectively accept or donate one or more 
electrons and become negatively or positively charged in the process are 
called radicals. 
• A chemical reaction involves the transformation of original substance into an 
altogether new substance(s). 
• A chemical reaction can be represented with the help of the symbols or the 
formulae of the elements and the compounds taking part in that reaction. This 
gives a chemical equation. 
• Certain necessary conditions for a chemical reaction to happen are — close 
contact, solution form, heat, light and catalyst. 
• Characteristics of chemical reactions are — change of colour, evolution of a gas, 
formation of a precipitate, change of state, change of smell and 
evolution/absorption of heat. 
• A complete chemical equation symbolically represents the reactants, products and 
their physical states. 
• The substances that react with each other are called reactants and they are 
represented on the left hand side of the equation. The substances that are formed 
as a result of the reaction are called products. They are represented on the right 
hand side of the equation. 
• A chemical equation needs to be balanced to make it follow the law of the 
conservation of mass. 
• The law of conservation of mass states that mass can be neither created nor 
destroyed, it can only be transformed from one form to another. 
• A chemical equation gives both qualitative and quantitative information about the 
reactants and products. 
Language of Chemistry 
ACTIVITY 1 
Write the names and symbols of the first twenty elements that you have studied 
in class VI & VII. 
Answer: 
 
 
 
 
ACTIVITY 2 
Write the molecular formulae of: 
1. Copper oxide 
2. Iron (III) chloride 
3. Sodium hydroxide 
4. Iron (II) sulphide 
5. Lead (II) oxide 
6. Hydrogen nitrate (nitric acid) 
7. Hydrogen sulphate (sulphuric acid) 
8. Calcium hydroxide 
9. Magnesium carbonate 
10. Ammonium carbonate 
Answer: 
1. Copper oxide – CuO 
2. Iron (III) chloride – FeCl3 
3. Sodium hydroxide – NaOH 
4. Iron (II) sulphide – FeS 
5. Lead (II) oxide – PbO 
6. Hydrogen nitrate (nitric acid) – HNO3 
7. Hydrogen sulphate (sulphuric acid) – H2SO4 
8. Calcium hydroxide – Ca(OH)2 
9. Magnesium carbonate – MgCO3 
10. Ammonium carbonate – (NH4)2CO3 
ACTIVITY 3 
Write the molecular formula for each of the following compounds: 
1. Sulphur trioxide 
2. Iron (II) sulphide and 
3. Ammonia 
Find the number and names of elements present in them and calculate their 
molecular masses. 
Answer: 
1. Sulphur trioxide 
1. A molecule of sulphur trioxide is represented by the formula SO3. 
2. The elements present in it are sulphur dioxide and oxygen. 
Page 4


Points to Remember: 
• The valency of an element is the number of electrons donated or accepted by its 
‘atom’ during chemical combination. 
• There are some elements with more than one valency e.g., iron, copper, tin, lead. 
• Two or more different non-metals that collectively accept or donate one or more 
electrons and become negatively or positively charged in the process are 
called radicals. 
• A chemical reaction involves the transformation of original substance into an 
altogether new substance(s). 
• A chemical reaction can be represented with the help of the symbols or the 
formulae of the elements and the compounds taking part in that reaction. This 
gives a chemical equation. 
• Certain necessary conditions for a chemical reaction to happen are — close 
contact, solution form, heat, light and catalyst. 
• Characteristics of chemical reactions are — change of colour, evolution of a gas, 
formation of a precipitate, change of state, change of smell and 
evolution/absorption of heat. 
• A complete chemical equation symbolically represents the reactants, products and 
their physical states. 
• The substances that react with each other are called reactants and they are 
represented on the left hand side of the equation. The substances that are formed 
as a result of the reaction are called products. They are represented on the right 
hand side of the equation. 
• A chemical equation needs to be balanced to make it follow the law of the 
conservation of mass. 
• The law of conservation of mass states that mass can be neither created nor 
destroyed, it can only be transformed from one form to another. 
• A chemical equation gives both qualitative and quantitative information about the 
reactants and products. 
Language of Chemistry 
ACTIVITY 1 
Write the names and symbols of the first twenty elements that you have studied 
in class VI & VII. 
Answer: 
 
 
 
 
ACTIVITY 2 
Write the molecular formulae of: 
1. Copper oxide 
2. Iron (III) chloride 
3. Sodium hydroxide 
4. Iron (II) sulphide 
5. Lead (II) oxide 
6. Hydrogen nitrate (nitric acid) 
7. Hydrogen sulphate (sulphuric acid) 
8. Calcium hydroxide 
9. Magnesium carbonate 
10. Ammonium carbonate 
Answer: 
1. Copper oxide – CuO 
2. Iron (III) chloride – FeCl3 
3. Sodium hydroxide – NaOH 
4. Iron (II) sulphide – FeS 
5. Lead (II) oxide – PbO 
6. Hydrogen nitrate (nitric acid) – HNO3 
7. Hydrogen sulphate (sulphuric acid) – H2SO4 
8. Calcium hydroxide – Ca(OH)2 
9. Magnesium carbonate – MgCO3 
10. Ammonium carbonate – (NH4)2CO3 
ACTIVITY 3 
Write the molecular formula for each of the following compounds: 
1. Sulphur trioxide 
2. Iron (II) sulphide and 
3. Ammonia 
Find the number and names of elements present in them and calculate their 
molecular masses. 
Answer: 
1. Sulphur trioxide 
1. A molecule of sulphur trioxide is represented by the formula SO3. 
2. The elements present in it are sulphur dioxide and oxygen. 
3. One molecule of sulphur trioxide has one atom of sulphur and three atoms of 
oxygen. 
4. Molecular mass of sulphur trioxide (SO3) 
= 32 + 3 x 16 
= 32 + 48 = 80 amu. 
2. Iron (II) sulphide 
1. A molecule of iron (II) sulphide is represented by the formula FeS. 
2. The elements present in it are iron and sulphur. 
3. One molecule of iron (II) sulphide has one atom of iron and one atom of sulphur. 
4. Molecular mass of iron (II) sulphide (FeS) 
= 55.5 + 32 
= 87.5 amu. 
3. Ammonia 
1. A molecule of ammonia is represented by the formula NH3. 
2. The elements present in it are nitrogen and hydrogen. 
3. One molecule of ammonia has one atom of nitrogen and three atoms of hydrogen. 
4. Molecular mass of ammonia (NH3) 
= 14 + 3 x 1 
= 14 + 3 
= 17 amu. 
Exercise 
Question 1. 
Define: 
(a) Radical 
(b) Valency 
(c) Molecular formula 
Answer: 
(a) Radical: A radical is an atom of an element or a group of atoms of different 
elements that behaves as a single unit with a positive or negative charge on it. 
(b) Valency: It is the number of electrons donated or accepted by the valence shell of 
an atom during chemical combination. 
(c) Molecular formula: It is a symbolic representation of a molecule. It shows the 
number of atoms of each element present in it. These atoms combine in whole number 
to form the molecule. 
Question 2. 
Give the symbols and valencies of following radicals: 
(a) Hydroxide (b) Chloride 
(c) Carbonate (d) ammonium 
Page 5


Points to Remember: 
• The valency of an element is the number of electrons donated or accepted by its 
‘atom’ during chemical combination. 
• There are some elements with more than one valency e.g., iron, copper, tin, lead. 
• Two or more different non-metals that collectively accept or donate one or more 
electrons and become negatively or positively charged in the process are 
called radicals. 
• A chemical reaction involves the transformation of original substance into an 
altogether new substance(s). 
• A chemical reaction can be represented with the help of the symbols or the 
formulae of the elements and the compounds taking part in that reaction. This 
gives a chemical equation. 
• Certain necessary conditions for a chemical reaction to happen are — close 
contact, solution form, heat, light and catalyst. 
• Characteristics of chemical reactions are — change of colour, evolution of a gas, 
formation of a precipitate, change of state, change of smell and 
evolution/absorption of heat. 
• A complete chemical equation symbolically represents the reactants, products and 
their physical states. 
• The substances that react with each other are called reactants and they are 
represented on the left hand side of the equation. The substances that are formed 
as a result of the reaction are called products. They are represented on the right 
hand side of the equation. 
• A chemical equation needs to be balanced to make it follow the law of the 
conservation of mass. 
• The law of conservation of mass states that mass can be neither created nor 
destroyed, it can only be transformed from one form to another. 
• A chemical equation gives both qualitative and quantitative information about the 
reactants and products. 
Language of Chemistry 
ACTIVITY 1 
Write the names and symbols of the first twenty elements that you have studied 
in class VI & VII. 
Answer: 
 
 
 
 
ACTIVITY 2 
Write the molecular formulae of: 
1. Copper oxide 
2. Iron (III) chloride 
3. Sodium hydroxide 
4. Iron (II) sulphide 
5. Lead (II) oxide 
6. Hydrogen nitrate (nitric acid) 
7. Hydrogen sulphate (sulphuric acid) 
8. Calcium hydroxide 
9. Magnesium carbonate 
10. Ammonium carbonate 
Answer: 
1. Copper oxide – CuO 
2. Iron (III) chloride – FeCl3 
3. Sodium hydroxide – NaOH 
4. Iron (II) sulphide – FeS 
5. Lead (II) oxide – PbO 
6. Hydrogen nitrate (nitric acid) – HNO3 
7. Hydrogen sulphate (sulphuric acid) – H2SO4 
8. Calcium hydroxide – Ca(OH)2 
9. Magnesium carbonate – MgCO3 
10. Ammonium carbonate – (NH4)2CO3 
ACTIVITY 3 
Write the molecular formula for each of the following compounds: 
1. Sulphur trioxide 
2. Iron (II) sulphide and 
3. Ammonia 
Find the number and names of elements present in them and calculate their 
molecular masses. 
Answer: 
1. Sulphur trioxide 
1. A molecule of sulphur trioxide is represented by the formula SO3. 
2. The elements present in it are sulphur dioxide and oxygen. 
3. One molecule of sulphur trioxide has one atom of sulphur and three atoms of 
oxygen. 
4. Molecular mass of sulphur trioxide (SO3) 
= 32 + 3 x 16 
= 32 + 48 = 80 amu. 
2. Iron (II) sulphide 
1. A molecule of iron (II) sulphide is represented by the formula FeS. 
2. The elements present in it are iron and sulphur. 
3. One molecule of iron (II) sulphide has one atom of iron and one atom of sulphur. 
4. Molecular mass of iron (II) sulphide (FeS) 
= 55.5 + 32 
= 87.5 amu. 
3. Ammonia 
1. A molecule of ammonia is represented by the formula NH3. 
2. The elements present in it are nitrogen and hydrogen. 
3. One molecule of ammonia has one atom of nitrogen and three atoms of hydrogen. 
4. Molecular mass of ammonia (NH3) 
= 14 + 3 x 1 
= 14 + 3 
= 17 amu. 
Exercise 
Question 1. 
Define: 
(a) Radical 
(b) Valency 
(c) Molecular formula 
Answer: 
(a) Radical: A radical is an atom of an element or a group of atoms of different 
elements that behaves as a single unit with a positive or negative charge on it. 
(b) Valency: It is the number of electrons donated or accepted by the valence shell of 
an atom during chemical combination. 
(c) Molecular formula: It is a symbolic representation of a molecule. It shows the 
number of atoms of each element present in it. These atoms combine in whole number 
to form the molecule. 
Question 2. 
Give the symbols and valencies of following radicals: 
(a) Hydroxide (b) Chloride 
(c) Carbonate (d) ammonium 
(e) Nitrate 
Answer: 
 
Question 3. 
Write the molecular formula for the oxide and sulphide of following elements. 
(a) Sodium (b) Calcium 
(c) Hydrogen 
Answer: 
(a) Sodium oxide Na2O 
Sodium sulphide Na2S 
(b) Calcium oxide CaO 
Calcium sulphide CaS 
(c) Hydrogen oxide H2O 
Hydrogen sulphide H2S 
Question 4. 
Write the molecular formulae for the following compounds and name the elements 
present. 
(a) Baking soda (b) Common salt 
(c) Sulphuric acid (d) Nitric acid 
Answer: 
(a) Baking soda — NaHCO3 
Elements present in Baking soda are sodium, hydrogen, oxygen and carbon. 
(b) Common salt — NaCl 
Element present are: Sodium and chlorine. 
(c) Sulphuric acid — H2SO4 
Element present are: Hydrogen, sulphur and oxygen. 
(d) Nitric acid — HNO3 
Elements present are: Hydrogen, nitrogen and oxygen. 
Question 5. 
The valency of aluminium is 3. Write the valency of other radicals present in the 
following compounds. 
(a) Aluminium chloride