Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 2.2 Structure of Matter offer valuable context and analysis.
WBBSE Class 8 Science Chapter 2.2 Question Answer – Structure of Matter
Multiple Choice Questions & Answers : (1 mark for each question)
Question 1.
In 1903 who had proposed the model of an atom, due to which electrons and protons were known to us?
i) Rutherford
ii) Dalton
iii) Goldstein
iv) Joseph J Thomson
Answer:
iv) Joseph J Thomson
Question 2.
The present concept of the structure of an atom is given by which scientiest?
i) Joseph J Thomson
ii) Goldstein
iii) Niles Bohr
iv) Rutherford
Answer:
iii) Niles Bohr
Question 3.
Which model does not able to explain the stability of an atom?
i) Thomson’s model
ii) Rutherford’s model
iii) Bhor’s model
iv) none of the above
Answer:
ii) Rutherford’s model
Question 4.
Name an atom in which the molecules of that atom does not contain any neutrons?
i) Hydrogen
ii) Oxygen
iii) Sodium
iv) Phosphorous
Answer:
i) Hydrogen
Question 5.
Electron was discovered by –
i) Goldstein
ii) J J Thomson
iii) Niles Bohr
iv) Rutherford
Answer:
iii) Niles Bohr
Question 6.
The correct electronic configuration of sodium is-
i) 8, 2, 1
ii) 2, 1, 8
iii) 2, 8, 2
iv) 2, 8, 1
Answer:
iv) 2, 8, 1
Question 7.
Who discovered neutron in 1953 ?
i) Niles Bohr
ii) James Chadwick
iii) Rutherford
iv) Goldstein
Answer:
ii) James Chadwick
Question 8.
The atom has-
i) Positive charge
ii) negative charge
iii) some times positive and sometimes negative
iv) no charge
Answer:
iv) no charge
Question 9.
Symbol of Ferric ion is –
i) Fe+1
ii) Fe+3
iii) Fe+
iv) Fe+4
Answer:
ii) Fe+3
Question 10.
Charged atoms are called-
i) isotope
ii) isobar
iii) isotone
iv) ion
Answer:
iv) lon.
Question 11.
The total number of protons and neutrons in an atom is called its
i) mass number
ii) atomic number
iii) mass
iv) none of the above
Answer:
Mtas number.
State whether True or False : (1 mark for each question)
1. Vearly the whole mass of an atom remains concentrated at its centers.
2. John Dalton’s experiment proved the existence of electrons in 1820.
3. Neutrons are electrically neutral.
4. An iron atom is heavier than a gold atom.
5. In a solid the average distance between the molecules is much larger that those in a solid.
6. The kinetic energy of molecules in a liquid increases with increase of temperature.
7. Salt (NaCl) melts at a temperature of about 800° C.
8. Ionic compounds are made of molecules.
9. Liquids have definite shape, but they have not definite volume.
10. The mass of an atom can not be measured directly by any balance.
Answer:
1. true
2. false
3. true
4. false
5. false
6. true
7. true
8. false
9. false
10. true
Fill in the blanks : (1 mark for each question)
1. In 1808 _________ published his atomic theory.
2. The smallest particle of an element that retains the properties of the element is called an ________.
3. Atoms of the same element possessing unequal number of neutrons are called _________.
4. Electrons are ________ charged.
5. The number of protons in an atom is called its _________.
6. The total number of protons and neutrons in an atom is called its ________.
7. The ________ has mass but no charge.
8. Atoms gain or lose ________ to attain stability.
9. When an atom gains or loses an electron, an ________ is formed.
10. When more than one atom combine to form an ion, it is called a ________.
11. Solids have their own shape and ________.
12. Atoms of differfnt elements differ in mass and ________ properties.
Answer:
1. John Dalton
2. atom
3. isotopes
4. negatively
5. atomic number
6. mass number
7. neutron
8. electrons
9. ion
10. radical
11. volume
12. chemical.
Match the following : (1 mark for each question)
a) Match the column A with column B.
Column A | Column B |
a) Formula of Ammonium | i) CaCO3 |
b) Nicls Bohar is a | ii) roughly views like solar system |
c) Formula of Calcium carbonate | iii) lins many valency |
d) Valency of Aluminium is | iv) has 4 protons. |
e) The atomic model | v) Plasma |
i) In Cuprous oxide | vi) NH4+ |
g) Iron | vii) Valency of copper is 1. |
h) Nuclars of an oxygen atom | viii) 3 |
i) Fourth state of a substance is | ix) renouned atom scientist |
Answer:
a) Formula of Ammonium NH4
b) Niels Bohr is a renoined atom scientist
c) Formula of Calcium Carbonate CaCO3
d) Valency of Aluminium 3.
e) The atomic model roughly views like solar system.
f) In Cuprous oxide valency of copper is 1.
g) Iron has many valency.
h) Nucleus of an oxyen atom has 4 protons.
i) Fourth state of a substance is plasma.
Very Short Questions & Answers : (1 mark for each question)
Question 1.
What does the word ‘atoms’ mean in Greck language?
Answer:
Indivisible
Question 2.
Who is the father of atomic theory?
Answer:
John Dalton.
Question 3.
In which year atomic theory of John Dalton was published?
Answer:
Atomic theory of John Dalton was published in 1808
Question 4.
What are an atom made up of?
Answer:
Atoms are made up of three smaller particles, called proton, neutron and electron.
Question 5.
Who discovered neutron?
Answer:
Neutron was discovered in 1912 by Rutherford’s pupil, Chadwick.
Question 6.
What is atomic number?
Answer:
The number of protons in an atom is called its atomic number.
Question 7.
What is mass number?
Answer:
The total number of protons and neutrons in an atom is called its mass number.
Question 8.
What is Isotope?
Answer:
Atoms of the same element possessing unequal number of neutrons are called isotopes. Examples are (protium), (doeterium). (tritium)
Question 9.
What is Isobar?
Answer:
Atoms different elements that have an equal mass number are called is obars of one another. Examples are… H and….He,… C and… N.
Question 10.
What are ions?
Answer:
The atoms which attain positive or negative charges due to gain or loss of one or more electrons are called ions.
Question 11.
What are cations?
Answer:
The positively charged ions formed by the loss of electrons from an atoms are called cations.
Question 12.
What are anions?
Answer:
The negatively charged ions formed by the gain of electrons by an atom are called anions.
Short Questions & Answers : (2 marks for each question)
Question 1.
What is Valency of an element?
Answer:
Valency of an element is a measure of its combining power with other atoms when it forms chemical compounds or molecules. The concept of velence was developed in the second half of the 19th century and helped successfuily to explain the molecular structure of inorganic and organic compounds.
Question 2.
How the pleasant smell of incense sticks spreads through a room?
Answer:
When a iscense stick burns, some volatile compounds present in it evaporate. Molecules of some of these compounds, when inhaled. gives as the sensation of pleasant smell. Spreading of an odour through air is due to motion of molecules in the gas phase.
Question 3.
How can you prove that molecules can spread through liquids?
Answer:
In a glass of water if we add a drop of ink, it spreads slowly through water. This experiment indicates that molecules can spread through liquids.
Question 4.
What are the characteristics of atoms and molecules in a solid?
Answer:
In a solid the atoms and molecules remain in a relatively ordered state and close to each other. In a solid, the atoms or molecules viabrate about their mean position.
Question 5.
What are the characteristics of molecoles in a liquid?
Answer:
Molecules in a liquid are somewhat disordered. They can viabrate, rotate and move through a small distance. This freedom of movement results in a liquid having no sefinite shape, although it does have a definite volume.
Question 6.
What are the characteristics of molecules in a gas?
Answer:
In a gas molecules are moving randomly with different speeds, vibrating and rotating. They are colliding with each other, and are also collifing against the walls of the container. Such incessant motion results in a gas having no xixed volume or shape.
Long Questions & Answers : (3 marks for each question)
Question 1.
What was Rutherford’s general conclusions about atom?
Answer:
- Most of the space inside an atom is empty.
- Nearly the whole mass of an atom remains concentrated at its centre. Rutherford named this heavy central part nucleus.
- The entire positive charge of an atom remains confined to its nucleus.
- Electrons revolve around thenucleus in various circular orbits
Question 2.
Describe Dalton’s Atomic Theory.
Answer:
Dalton proposed the following postulates about the structure of matter-
- All matter is made up of indivisible minute particles called atoms.
- All atoms of an element are identical
- Atoms of an element are different from the atoms of any other element.
- A compound is formed by the combination of atoms of two or more elements in simple ratios.
- Atoms can neither be created nor destroyed.
Question 3.
Describe the structure of electrovalent compound NaCl.
Answer:
NaCl is an electro valent compound.
Electrons arranged in Na are 2 + 8 + 1
Electrons areanged in CL are 2 + 8 + 7
Sodium has I lectron in its valence shell. Chtorine has 7 electrons in its valence shell, which is I short of the octet. Sodium atom loses I electron toi necame Na–. Chlorine atom gains this electron to become Cl
Na → Na–
2 + 8 + 12 + 8
Cl → Cl–
2 + 8 + 72 + 8 + 8
Thus NaCl compound is formed.
Question 4.
What happens when the temperature of a solid is increased?
Answer:
In a solid atoms and molecules vibrate at all temperatures. When temperature is increased kinetic energy of vibration increases. Beyond a certain pointthe vibration became so snergetic that the solid state can not be maintained and the solid is converted to a liquid. This conversion is known as melting.
Question 5.
What happens when the temperature of a liquid is increased?
Answer:
With increase of temperature, kinetic energy of molecules in a liquid increases. Beyond a certain point, the kinetic energy becomes so great that molecules can not be held back in the liquid state. The liquid is then converted to its vapour. This change of state is called boiling.
Question 6.
In the following table, diagrams of the atoms of lithium, sodium, magnesium and chlorine are shown. Complete the table with information regarding the quantities mentioned in it.
Answer: