Selina Textbook Solutions: Elements, Compounds, Symbols, And Formulae | Chemistry Class 6 ICSE PDF Download

 Page 1


POINTS TO REMEMBER 
1. Pure substances : “A single substance of definite composition.” Pure substances 
are homogeneous. They are made up of only one kind of atoms and compounds 
or made up of only one kind of molecules. 
2. Elements : An element is defined as a pure substance made up of only one kind 
of atoms that cannot be converted into anything simpler than itself by any physical 
or chemical process. 
3. Metals : Most of the elements known to us are metals. Example: Sodium 
potassium, iron, gold, silver are elements. Metals are lustrous, hard, ductile and 
malleable, good conductor of electricity. Mercury (liquid) have High M.P. and High 
B.P. but exceptions are there. 
4. Non-metals : Carbon, phosphorous, sulphur all solids, Bromine (liquid) iodine(s) 
and rest are gases, dull, do not shine. Cannot be drawn into wires, non malleable, 
have low M.P. and B.P. do not produce sound when struck, do not conduct 
electricity. Exceptions are there. 
5. Boron, sillicon, arsenic, antimony resemble both metals and non-metals and are 
called metalloids. 
6. Unreactive gases, also called noble gases are gases which are very unreactive 
i.e. He, Ne Ar, Kr, xenon and radon. 
7. Symbols are abbreviations that are used to denote a chemical element which is 
usually first letter of its name in English or Latin. 
8. O is the symbol of element oxygen. 
C is symbol of element carbon. 
Cu is symbol of element copper (taken from Latin name Cuprum) 
9. Compound is formed by the chemical combination of two or more elements in 
definite ratio (by mass). 
10. Molecule is the smallest unit of a compound. 
11. Elements are the basic substances from which all other substances are made. 
12. Compound : Consist of two or more elements combined in definite proportion, 
pure and homogeneous, physical and chemical properties are entirely new and 
different from its consititutent elements, energy is either needed or produced when 
a compound is formed. 
13. Atoms : Atom is the smallest unit of an element which cannot be further broken 
into simpler parts, may or may not have independent existence. 
14. Molecule of element : When two or more atoms of the same element combine it 
forms a molecule of an atom. e.g. N 2,O 2 
15. Molecule of compounds : When atoms of two or more element combine, they 
form a molecule of a compound. H 20, HC1, CuSO 4. 
EXERCISE-I 
Question 1. 
Classify the following substances into elements and compounds. 
Answer: 
Mercury, sulphur, sugar, water, sand, gold, coal, oxygen, alcohol. 
Page 2


POINTS TO REMEMBER 
1. Pure substances : “A single substance of definite composition.” Pure substances 
are homogeneous. They are made up of only one kind of atoms and compounds 
or made up of only one kind of molecules. 
2. Elements : An element is defined as a pure substance made up of only one kind 
of atoms that cannot be converted into anything simpler than itself by any physical 
or chemical process. 
3. Metals : Most of the elements known to us are metals. Example: Sodium 
potassium, iron, gold, silver are elements. Metals are lustrous, hard, ductile and 
malleable, good conductor of electricity. Mercury (liquid) have High M.P. and High 
B.P. but exceptions are there. 
4. Non-metals : Carbon, phosphorous, sulphur all solids, Bromine (liquid) iodine(s) 
and rest are gases, dull, do not shine. Cannot be drawn into wires, non malleable, 
have low M.P. and B.P. do not produce sound when struck, do not conduct 
electricity. Exceptions are there. 
5. Boron, sillicon, arsenic, antimony resemble both metals and non-metals and are 
called metalloids. 
6. Unreactive gases, also called noble gases are gases which are very unreactive 
i.e. He, Ne Ar, Kr, xenon and radon. 
7. Symbols are abbreviations that are used to denote a chemical element which is 
usually first letter of its name in English or Latin. 
8. O is the symbol of element oxygen. 
C is symbol of element carbon. 
Cu is symbol of element copper (taken from Latin name Cuprum) 
9. Compound is formed by the chemical combination of two or more elements in 
definite ratio (by mass). 
10. Molecule is the smallest unit of a compound. 
11. Elements are the basic substances from which all other substances are made. 
12. Compound : Consist of two or more elements combined in definite proportion, 
pure and homogeneous, physical and chemical properties are entirely new and 
different from its consititutent elements, energy is either needed or produced when 
a compound is formed. 
13. Atoms : Atom is the smallest unit of an element which cannot be further broken 
into simpler parts, may or may not have independent existence. 
14. Molecule of element : When two or more atoms of the same element combine it 
forms a molecule of an atom. e.g. N 2,O 2 
15. Molecule of compounds : When atoms of two or more element combine, they 
form a molecule of a compound. H 20, HC1, CuSO 4. 
EXERCISE-I 
Question 1. 
Classify the following substances into elements and compounds. 
Answer: 
Mercury, sulphur, sugar, water, sand, gold, coal, oxygen, alcohol. 
Ans. Element: Mercury, sulphur, gold, coal, oxygen. 
Compound : Sugar, water, sand, alcohol. 
Question 2. 
Give the symbols of: Carbon, calcium, copper, chlorine, cobalt, argon. 
Answer: 
Carbon is C         Chlorine is Cl 
Calcium is Ca     Cobalt is Co 
Copper is Cu       Argon is Ar 
Question 3. 
Define a pure substance. How many types of pure substances do you know ? 
Answer: 
Pure substances : “A substance of a definite composition which has consistent 
properties throughout, is called a pure substance” 
Types of pure substances: Pure substances are of two 
types (i) Elements, (ii) Compounds. 
Question 4. 
Define : (a) Elements (b) Compounds. 
Name the particles from which elements and compounds are made of. 
Answer: 
(a) Elements : An element is defined as a pure substance made up of only one kind of 
atoms that cannot be converted into anything simpler than itself by any physical or 
chemical process. 
(b) Compounds : Compounds are pure substances composed of two or more elements 
in definite proportion by mass and has a definite set of properties. Compound is made 
up of only one kind of molecules. 
Question 5. 
Give two examples for each of the following : 
(a) Metals 
(b) Non-metals 
(c) Metalloids 
(d) Noble gases 
Answer: 
(a) Metals : Iron, silver, gold. 
(b) Non-metals : Carbon, sulphur, oxygen. 
(c) Metalloids : Antimony, silicon, boron. 
(d) Noble gases : Helium, argon, neon. 
Question 6. 
Name the elements which form water. How will you justify that water is a compound ? 
Answer: 
Page 3


POINTS TO REMEMBER 
1. Pure substances : “A single substance of definite composition.” Pure substances 
are homogeneous. They are made up of only one kind of atoms and compounds 
or made up of only one kind of molecules. 
2. Elements : An element is defined as a pure substance made up of only one kind 
of atoms that cannot be converted into anything simpler than itself by any physical 
or chemical process. 
3. Metals : Most of the elements known to us are metals. Example: Sodium 
potassium, iron, gold, silver are elements. Metals are lustrous, hard, ductile and 
malleable, good conductor of electricity. Mercury (liquid) have High M.P. and High 
B.P. but exceptions are there. 
4. Non-metals : Carbon, phosphorous, sulphur all solids, Bromine (liquid) iodine(s) 
and rest are gases, dull, do not shine. Cannot be drawn into wires, non malleable, 
have low M.P. and B.P. do not produce sound when struck, do not conduct 
electricity. Exceptions are there. 
5. Boron, sillicon, arsenic, antimony resemble both metals and non-metals and are 
called metalloids. 
6. Unreactive gases, also called noble gases are gases which are very unreactive 
i.e. He, Ne Ar, Kr, xenon and radon. 
7. Symbols are abbreviations that are used to denote a chemical element which is 
usually first letter of its name in English or Latin. 
8. O is the symbol of element oxygen. 
C is symbol of element carbon. 
Cu is symbol of element copper (taken from Latin name Cuprum) 
9. Compound is formed by the chemical combination of two or more elements in 
definite ratio (by mass). 
10. Molecule is the smallest unit of a compound. 
11. Elements are the basic substances from which all other substances are made. 
12. Compound : Consist of two or more elements combined in definite proportion, 
pure and homogeneous, physical and chemical properties are entirely new and 
different from its consititutent elements, energy is either needed or produced when 
a compound is formed. 
13. Atoms : Atom is the smallest unit of an element which cannot be further broken 
into simpler parts, may or may not have independent existence. 
14. Molecule of element : When two or more atoms of the same element combine it 
forms a molecule of an atom. e.g. N 2,O 2 
15. Molecule of compounds : When atoms of two or more element combine, they 
form a molecule of a compound. H 20, HC1, CuSO 4. 
EXERCISE-I 
Question 1. 
Classify the following substances into elements and compounds. 
Answer: 
Mercury, sulphur, sugar, water, sand, gold, coal, oxygen, alcohol. 
Ans. Element: Mercury, sulphur, gold, coal, oxygen. 
Compound : Sugar, water, sand, alcohol. 
Question 2. 
Give the symbols of: Carbon, calcium, copper, chlorine, cobalt, argon. 
Answer: 
Carbon is C         Chlorine is Cl 
Calcium is Ca     Cobalt is Co 
Copper is Cu       Argon is Ar 
Question 3. 
Define a pure substance. How many types of pure substances do you know ? 
Answer: 
Pure substances : “A substance of a definite composition which has consistent 
properties throughout, is called a pure substance” 
Types of pure substances: Pure substances are of two 
types (i) Elements, (ii) Compounds. 
Question 4. 
Define : (a) Elements (b) Compounds. 
Name the particles from which elements and compounds are made of. 
Answer: 
(a) Elements : An element is defined as a pure substance made up of only one kind of 
atoms that cannot be converted into anything simpler than itself by any physical or 
chemical process. 
(b) Compounds : Compounds are pure substances composed of two or more elements 
in definite proportion by mass and has a definite set of properties. Compound is made 
up of only one kind of molecules. 
Question 5. 
Give two examples for each of the following : 
(a) Metals 
(b) Non-metals 
(c) Metalloids 
(d) Noble gases 
Answer: 
(a) Metals : Iron, silver, gold. 
(b) Non-metals : Carbon, sulphur, oxygen. 
(c) Metalloids : Antimony, silicon, boron. 
(d) Noble gases : Helium, argon, neon. 
Question 6. 
Name the elements which form water. How will you justify that water is a compound ? 
Answer: 
The elements which form water are (i) Hydrogen and oxygen. 
Justification : Water has entirely different properties (i.e. is a liquid, extinguishes fire) 
from the elements it is made up of i.e. Hydrogen a gas catches fire oxygen a gas 
supporter of combustion. 
1. Energy is needed to form water on combining O 2 with H 2. 
2. We can not seperate the constituents of water by simple physical means. 
Question 7. 
Give three differences between metals and non-metals. 
Answer: 
Metals 
1. Metals are ductile i.e. can be drawn into wires. 
2. Metals are malleable i.e. can be beaten to form sheets. 
3. They are sonorous. 
Non-metals 
1. Non-metals are mostly soft solids cannot be drawn into wires. 
2. They are mostly gases and are not malleable. 
3. They donot produce sound when struck. 
Question 8. 
How is sodium chloride different from its constituent elements, sodium and chlorine ? 
Answer: 
Sodium is a metal that is stored in kerosene oil as it reacts very fast with air and water. 
Chlorine is a reactive greenish yellow gas which is poisonous. When these two 
elements combine chemically they form common salt sodium chloride which is non 
poisonous colourless solid substance that we use in our food to add taste and to obtain 
some nutrition. 
Question 9. 
State four important characteristics of compounds. 
Answer: 
1. When compound is formed energy like heat, light or electricity is either needed or 
produced. 
2. A compound has properties entirely different from the properties of its 
constituents. 
3. Change in weight takes place. 
4. It cannot be separated into its constituents by simple physical means. 
Page 4


POINTS TO REMEMBER 
1. Pure substances : “A single substance of definite composition.” Pure substances 
are homogeneous. They are made up of only one kind of atoms and compounds 
or made up of only one kind of molecules. 
2. Elements : An element is defined as a pure substance made up of only one kind 
of atoms that cannot be converted into anything simpler than itself by any physical 
or chemical process. 
3. Metals : Most of the elements known to us are metals. Example: Sodium 
potassium, iron, gold, silver are elements. Metals are lustrous, hard, ductile and 
malleable, good conductor of electricity. Mercury (liquid) have High M.P. and High 
B.P. but exceptions are there. 
4. Non-metals : Carbon, phosphorous, sulphur all solids, Bromine (liquid) iodine(s) 
and rest are gases, dull, do not shine. Cannot be drawn into wires, non malleable, 
have low M.P. and B.P. do not produce sound when struck, do not conduct 
electricity. Exceptions are there. 
5. Boron, sillicon, arsenic, antimony resemble both metals and non-metals and are 
called metalloids. 
6. Unreactive gases, also called noble gases are gases which are very unreactive 
i.e. He, Ne Ar, Kr, xenon and radon. 
7. Symbols are abbreviations that are used to denote a chemical element which is 
usually first letter of its name in English or Latin. 
8. O is the symbol of element oxygen. 
C is symbol of element carbon. 
Cu is symbol of element copper (taken from Latin name Cuprum) 
9. Compound is formed by the chemical combination of two or more elements in 
definite ratio (by mass). 
10. Molecule is the smallest unit of a compound. 
11. Elements are the basic substances from which all other substances are made. 
12. Compound : Consist of two or more elements combined in definite proportion, 
pure and homogeneous, physical and chemical properties are entirely new and 
different from its consititutent elements, energy is either needed or produced when 
a compound is formed. 
13. Atoms : Atom is the smallest unit of an element which cannot be further broken 
into simpler parts, may or may not have independent existence. 
14. Molecule of element : When two or more atoms of the same element combine it 
forms a molecule of an atom. e.g. N 2,O 2 
15. Molecule of compounds : When atoms of two or more element combine, they 
form a molecule of a compound. H 20, HC1, CuSO 4. 
EXERCISE-I 
Question 1. 
Classify the following substances into elements and compounds. 
Answer: 
Mercury, sulphur, sugar, water, sand, gold, coal, oxygen, alcohol. 
Ans. Element: Mercury, sulphur, gold, coal, oxygen. 
Compound : Sugar, water, sand, alcohol. 
Question 2. 
Give the symbols of: Carbon, calcium, copper, chlorine, cobalt, argon. 
Answer: 
Carbon is C         Chlorine is Cl 
Calcium is Ca     Cobalt is Co 
Copper is Cu       Argon is Ar 
Question 3. 
Define a pure substance. How many types of pure substances do you know ? 
Answer: 
Pure substances : “A substance of a definite composition which has consistent 
properties throughout, is called a pure substance” 
Types of pure substances: Pure substances are of two 
types (i) Elements, (ii) Compounds. 
Question 4. 
Define : (a) Elements (b) Compounds. 
Name the particles from which elements and compounds are made of. 
Answer: 
(a) Elements : An element is defined as a pure substance made up of only one kind of 
atoms that cannot be converted into anything simpler than itself by any physical or 
chemical process. 
(b) Compounds : Compounds are pure substances composed of two or more elements 
in definite proportion by mass and has a definite set of properties. Compound is made 
up of only one kind of molecules. 
Question 5. 
Give two examples for each of the following : 
(a) Metals 
(b) Non-metals 
(c) Metalloids 
(d) Noble gases 
Answer: 
(a) Metals : Iron, silver, gold. 
(b) Non-metals : Carbon, sulphur, oxygen. 
(c) Metalloids : Antimony, silicon, boron. 
(d) Noble gases : Helium, argon, neon. 
Question 6. 
Name the elements which form water. How will you justify that water is a compound ? 
Answer: 
The elements which form water are (i) Hydrogen and oxygen. 
Justification : Water has entirely different properties (i.e. is a liquid, extinguishes fire) 
from the elements it is made up of i.e. Hydrogen a gas catches fire oxygen a gas 
supporter of combustion. 
1. Energy is needed to form water on combining O 2 with H 2. 
2. We can not seperate the constituents of water by simple physical means. 
Question 7. 
Give three differences between metals and non-metals. 
Answer: 
Metals 
1. Metals are ductile i.e. can be drawn into wires. 
2. Metals are malleable i.e. can be beaten to form sheets. 
3. They are sonorous. 
Non-metals 
1. Non-metals are mostly soft solids cannot be drawn into wires. 
2. They are mostly gases and are not malleable. 
3. They donot produce sound when struck. 
Question 8. 
How is sodium chloride different from its constituent elements, sodium and chlorine ? 
Answer: 
Sodium is a metal that is stored in kerosene oil as it reacts very fast with air and water. 
Chlorine is a reactive greenish yellow gas which is poisonous. When these two 
elements combine chemically they form common salt sodium chloride which is non 
poisonous colourless solid substance that we use in our food to add taste and to obtain 
some nutrition. 
Question 9. 
State four important characteristics of compounds. 
Answer: 
1. When compound is formed energy like heat, light or electricity is either needed or 
produced. 
2. A compound has properties entirely different from the properties of its 
constituents. 
3. Change in weight takes place. 
4. It cannot be separated into its constituents by simple physical means. 
Question 10. 
Give two examples for each of the following : 
(a) Non-metals which are solids 
(b) Metals which are soft 
(c) Non-metals which are lustrous 
(d) Elements which are liquids. 
(e) Inert gases 
(f) Metalloids 
Answer: 
(a) Phosphorus, Sulphur 
(b) Lead and Sodium 
(c) Radium, Graphite 
(d) Mercury, Bromine 
(e) Helium, Neon 
(f) Antimony, Arsenic 
Question 11. 
Name the elements present 
(a) Sugar 
(b) Ammonia 
(c) Marble 
(d) Washing soda 
Answer: 
Compounds 
(a) Sugar 
(b) Ammonia 
(c) Marble 
(d) Washing soda 
Elements present 
(a) Carbon, hydrogen & oxygen 
(b) Nitrogen and hydrogen 
(c) Calcium, carbon & oxygen 
(d) Sodium, carbon & oxygen 
Question 12. 
What is the proportion of elements present in the following compounds? 
(a) H2O 
Page 5


POINTS TO REMEMBER 
1. Pure substances : “A single substance of definite composition.” Pure substances 
are homogeneous. They are made up of only one kind of atoms and compounds 
or made up of only one kind of molecules. 
2. Elements : An element is defined as a pure substance made up of only one kind 
of atoms that cannot be converted into anything simpler than itself by any physical 
or chemical process. 
3. Metals : Most of the elements known to us are metals. Example: Sodium 
potassium, iron, gold, silver are elements. Metals are lustrous, hard, ductile and 
malleable, good conductor of electricity. Mercury (liquid) have High M.P. and High 
B.P. but exceptions are there. 
4. Non-metals : Carbon, phosphorous, sulphur all solids, Bromine (liquid) iodine(s) 
and rest are gases, dull, do not shine. Cannot be drawn into wires, non malleable, 
have low M.P. and B.P. do not produce sound when struck, do not conduct 
electricity. Exceptions are there. 
5. Boron, sillicon, arsenic, antimony resemble both metals and non-metals and are 
called metalloids. 
6. Unreactive gases, also called noble gases are gases which are very unreactive 
i.e. He, Ne Ar, Kr, xenon and radon. 
7. Symbols are abbreviations that are used to denote a chemical element which is 
usually first letter of its name in English or Latin. 
8. O is the symbol of element oxygen. 
C is symbol of element carbon. 
Cu is symbol of element copper (taken from Latin name Cuprum) 
9. Compound is formed by the chemical combination of two or more elements in 
definite ratio (by mass). 
10. Molecule is the smallest unit of a compound. 
11. Elements are the basic substances from which all other substances are made. 
12. Compound : Consist of two or more elements combined in definite proportion, 
pure and homogeneous, physical and chemical properties are entirely new and 
different from its consititutent elements, energy is either needed or produced when 
a compound is formed. 
13. Atoms : Atom is the smallest unit of an element which cannot be further broken 
into simpler parts, may or may not have independent existence. 
14. Molecule of element : When two or more atoms of the same element combine it 
forms a molecule of an atom. e.g. N 2,O 2 
15. Molecule of compounds : When atoms of two or more element combine, they 
form a molecule of a compound. H 20, HC1, CuSO 4. 
EXERCISE-I 
Question 1. 
Classify the following substances into elements and compounds. 
Answer: 
Mercury, sulphur, sugar, water, sand, gold, coal, oxygen, alcohol. 
Ans. Element: Mercury, sulphur, gold, coal, oxygen. 
Compound : Sugar, water, sand, alcohol. 
Question 2. 
Give the symbols of: Carbon, calcium, copper, chlorine, cobalt, argon. 
Answer: 
Carbon is C         Chlorine is Cl 
Calcium is Ca     Cobalt is Co 
Copper is Cu       Argon is Ar 
Question 3. 
Define a pure substance. How many types of pure substances do you know ? 
Answer: 
Pure substances : “A substance of a definite composition which has consistent 
properties throughout, is called a pure substance” 
Types of pure substances: Pure substances are of two 
types (i) Elements, (ii) Compounds. 
Question 4. 
Define : (a) Elements (b) Compounds. 
Name the particles from which elements and compounds are made of. 
Answer: 
(a) Elements : An element is defined as a pure substance made up of only one kind of 
atoms that cannot be converted into anything simpler than itself by any physical or 
chemical process. 
(b) Compounds : Compounds are pure substances composed of two or more elements 
in definite proportion by mass and has a definite set of properties. Compound is made 
up of only one kind of molecules. 
Question 5. 
Give two examples for each of the following : 
(a) Metals 
(b) Non-metals 
(c) Metalloids 
(d) Noble gases 
Answer: 
(a) Metals : Iron, silver, gold. 
(b) Non-metals : Carbon, sulphur, oxygen. 
(c) Metalloids : Antimony, silicon, boron. 
(d) Noble gases : Helium, argon, neon. 
Question 6. 
Name the elements which form water. How will you justify that water is a compound ? 
Answer: 
The elements which form water are (i) Hydrogen and oxygen. 
Justification : Water has entirely different properties (i.e. is a liquid, extinguishes fire) 
from the elements it is made up of i.e. Hydrogen a gas catches fire oxygen a gas 
supporter of combustion. 
1. Energy is needed to form water on combining O 2 with H 2. 
2. We can not seperate the constituents of water by simple physical means. 
Question 7. 
Give three differences between metals and non-metals. 
Answer: 
Metals 
1. Metals are ductile i.e. can be drawn into wires. 
2. Metals are malleable i.e. can be beaten to form sheets. 
3. They are sonorous. 
Non-metals 
1. Non-metals are mostly soft solids cannot be drawn into wires. 
2. They are mostly gases and are not malleable. 
3. They donot produce sound when struck. 
Question 8. 
How is sodium chloride different from its constituent elements, sodium and chlorine ? 
Answer: 
Sodium is a metal that is stored in kerosene oil as it reacts very fast with air and water. 
Chlorine is a reactive greenish yellow gas which is poisonous. When these two 
elements combine chemically they form common salt sodium chloride which is non 
poisonous colourless solid substance that we use in our food to add taste and to obtain 
some nutrition. 
Question 9. 
State four important characteristics of compounds. 
Answer: 
1. When compound is formed energy like heat, light or electricity is either needed or 
produced. 
2. A compound has properties entirely different from the properties of its 
constituents. 
3. Change in weight takes place. 
4. It cannot be separated into its constituents by simple physical means. 
Question 10. 
Give two examples for each of the following : 
(a) Non-metals which are solids 
(b) Metals which are soft 
(c) Non-metals which are lustrous 
(d) Elements which are liquids. 
(e) Inert gases 
(f) Metalloids 
Answer: 
(a) Phosphorus, Sulphur 
(b) Lead and Sodium 
(c) Radium, Graphite 
(d) Mercury, Bromine 
(e) Helium, Neon 
(f) Antimony, Arsenic 
Question 11. 
Name the elements present 
(a) Sugar 
(b) Ammonia 
(c) Marble 
(d) Washing soda 
Answer: 
Compounds 
(a) Sugar 
(b) Ammonia 
(c) Marble 
(d) Washing soda 
Elements present 
(a) Carbon, hydrogen & oxygen 
(b) Nitrogen and hydrogen 
(c) Calcium, carbon & oxygen 
(d) Sodium, carbon & oxygen 
Question 12. 
What is the proportion of elements present in the following compounds? 
(a) H2O 
(b) CO2 
(c) CaO 
(d) NO2 
Answer: 
 
 
Question 13. 
Name two compounds which dissolve in water. 
Answer: 
Two compounds which dissolve in water are sugar, table salt. 
EXERCISE-II 
(ATOMS & MOLECULES) 
Question 1. 
Define: 
(a) Atom 
(b) Molecule 
(c) Atomicity 
(d) Formula 
Answer: 
(a) Atom : An atom is the smallest indivisible unit of an element which exhibits all the 
properties of that element and may or may not have independent existence. 
(b) Molecule : A molecule can be defined as the smallest unit of an element or a 
compound which exhibits all the properties of that element or compound and has 
independent existence. They are divisible into atoms. 
(c) Atomicity : The number of atoms in a molecule of an element is called its atomicity. 
(d) Formula : Formula is a short way of representing the molecule of an element or a 
compound. 
Question 2. 
Why are symbols and formulae of substances important?