Samacheer Kalvi 9th Science Solutions Chapter 11 Pdf
Tamilnadu Board Samacheer Kalvi 9th Science Solutions Chapter 11: Tamilnadu State Board Solution Class 9 Science Chapter 11 – ATOMIC STRUCTURE.
Samacheer Kalvi 9th Science Solutions Chapter 11: Overview
| Board | Samacheer Kalvi |
| Class | 9 |
| Subject | Science |
| Chapter | 11 |
| Chapter Name | ATOMIC STRUCTURE |
Samacheer Kalvi 9th Science Solutions Chapter 11 Pdf
Chapter 11
Atomic Structure
Exercise:
I. Choose the correct answer.
1) Among the following the odd pair is
a) O, F
b) Ar, N
c) Si, P
d) Cr, K
Ans: b) Ar, N
Because, Ar is Nobel gas and N is non-metal.
2) Change in the number of neutrons in an atom changes it to
a) An ion.
b) An isotope.
c) An isobar.
d) Another element.
Ans: b) An isotope.
Because, isotopes are the elements having same atomic no. but different mass no.
3) The term nucleons refer to a) Protons and electrons
b) Only neutrons
c) Electrons and neutrons
d) Protons and neutrons
Ans: d) Protons and neutrons
Because, in the nucleus positively charged protons and neutral neutrons are present.
4) The number of protons, neutrons and electrons present respectively in Br are
a) 80, 80, 35
b) 35, 55, 80
c) 35, 35, 80
d) 35, 45, 35
Ans: d) 35, 45, 35
Because, the atomic no. of Bromine is 35 and mass no. is 80.
5) The correct electronic configuration of potassium is
a) 2, 8, 9
b) 2, 8, 1
c) 2,8,8,1
d) 2,8,8,3
Ans:c) 2,8,8,1
Because, the atomic no. of Potassium is 19.
II. State true or false. If false, correct the statement.
1) In an atom, electrons revolve around the nucleus in fixed orbits.
Ans: True
Because of the electrostatic force of attraction between electrons and nucleus, electrons are revolving around the nucleus in fixed orbits.
2) Isotopes of an element have different atomic numbers.
Ans: False
Because, isotopes are the elements having same atomic no. but different mass no.
3) Electrons have negligible mass and charge.
Ans: False
Because, electrons have negligible mass and negative charge.
4) Smaller the size of the orbit, lower is the energy of the orbit.
Ans: True
Because, the orbits nearest to the nucleus are having less energy and which are smaller in size also.
5) The maximum number of electron in L Shell is 10.
Ans: False
Because, the maximum no. of electrons in L shell is 8.
III. Fill in the blanks.
1)) Calcium and Argon are examples of a pair of _________________
Ans: Calcium and Argon are examples of a pair of isobars.
Because, they are having same mass no. but different atomic no.
2) Total number of electrons that can be accommodated in an orbit is given by ______________
Ans: Total number of electrons that can be accommodated in an orbit is given by2n2,where n is no. of orbit.
3) _____________ Isotope is used in the nuclear reactors.
Ans: Radio isotopes is used in the nuclear reactors.
Because, this isotopes are unstable and having extra neutrons in their nuclei.
4) The number of neutrons present in Li is ___________
Ans: The number of neutrons present in Li is4.
Because, it has atomic no. as 3 and mass no. as 7.
5) The valency of Argon is ___________
Ans: The valency of Argon is zero.
Because, it has atomic no. 18 and electronic configuration as 2, 8, 8 that means its outermost shell i.e. valence shell is completely filled.
IV. Match the following.
1. Dalton : First atomic theory
2. Chadwick : Discovery of neutrons
3. Rutherford : Discovery of nucleus
4. Neil’s Bohr : Hydrogen atom model
V. Complete the following table.
Atomic no. Mass no. No. of neutrons No. of protons No. of electrons Name of the element
| Atomic no. | Mass no. | No. of neutrons | No. of protons | No. of electrons | Name of the element |
| 9 | 19 | 10 | 9 | 9 | Fluorine |
| 16 | 32 | 16 | 16 | 16 | Sulphur |
| 12 | 24 | 12 | 12 | 12 | Magnesium |
| 1 | 2 | 1 | 1 | 1 | Deuterium |
| 1 | 1 | 0 | 1 | 1 | Hydrogen |
VI. Answer very briefly.
1) Name an element which has the same number of electrons in its first and second shell.
Ans: Beryllium is the element which has same number of electrons in its first and second shell. The electronic configuration of beryllium having atomic number 4 is 1s2 2s2, that means it has 2 electrons in K shell and 2 electrons in L shell.
2) Write the electronic configuration of K and Cl.
Ans: The atomic number of potassium K is 19 having electronic configuration as 2, 8, 8, 1. The atomic number of chlorine Cl is 17 having electronic configuration as 2, 8, 7.
3) Write down the names of the particles represented by the following symbols and explain the meaning of superscript and subscript numbers attached. 1H1, 0n1, –1e0
Ans: The symbol 1H1 has the name as proton. The superscript represents the presence of 1 proton and subscript represents the charge which is +1. The symbol0n1 has the name as neutron. The superscript represents the presence of 1 neutron and subscript represents the charge which is zero or neutral. The symbol–1e0has the name as electron. The superscript represents the presence of 0 protons and neutrons, subscript represents the charge which is -1.
4) For an atom ‘X’, K, L and M shells are completely filled. How many electrons will be present in it?
Ans: Total number of electrons that can be accommodated in an orbit is given by2n2, where n is no. of orbit. For K shell n = 1, hence it has maximum 2 electrons. For L shell n = 2, hence it has maximum 8 electrons. For M shell n = 3 hence it has maximum 18 electrons. For an atom X, K, L and shells are completely filled means is has total electrons = 2 + 8 + 18 = 28 electrons.
5) What is the same about the electron structures of?
Ans: a) Lithium, Sodium and Potassium:
The atomic no. of Lithium is 3 and electronic configuration is 2, 1. The atomic no. of Sodium is 11 and electronic configuration is 2, 8, 1. The atomic no. of Potassium is 19 and electronic configuration is 2, 8, 8, 1. From this we conclude that, the valences of Lithium, Sodium and Potassium is same and it is 1.
b) Beryllium, Magnesium and Calcium:
The atomic no. of Beryllium is 4 and electronic configuration is 2, 2. The atomic no. of Magnesium is 12 and electronic configuration is 2, 8, 2. The atomic no. of Calcium is 20 and electronic configuration is 2, 8, 8, 2. From this we conclude that, the valences of Beryllium, Magnesium and Calcium is same and it is 2.
VII. Answer briefly.
1) How was it shown that atom has empty space?
Ans: In 1911, the scientist Lord Rutherford performed a famous experiment by bombarding alpha particles on the thin gold foil. He had chosen the gold because gold is the most malleable metal and he want to make a thin layer as possible. The conclusions made from this gold foil experiment are as follows: It was observed that most of the alpha particles are scattered in a straight line through the foil. Some of th alpha particles get deflected from their original path of scattering. And very few alpha particles are completely bounced back. From this observations Rutherford conclude that, The atom consist of a large empty space. The positively charged alpha particles get reflected and deflected from the positive charge inside the atom. And he named this positive charged space inside the atom as nucleus.
2) Why do 35Cl17 and 37Cl17have the same chemical properties? In what respect do these atoms differ?
Ans: 35Cl17 and 37Cl17 are the isotopes and hence their chemical properties are same. Isotopes are the different atoms of the same element having same atomic no. but different mass no. here the mass no of two chlorine atoms is different but they have same mass no. hence they are called as isotopes But, here the two chlorine atoms have same chemical properties. And due to the difference in their atomic mass no. they differ in physical contents.
3) Draw the structure of oxygen and sulphur atoms.
Ans:
Fig. Structure of oxygen atom and structure of Sulphur atom
The atomic no. of oxygen atom is 8, and it has 8 electrons, 8 protons and 8 neutrons. And hence the mass no. of oxygen is 16. The atomic no. of sulphur atom is 16, and it has 16 electrons, 16 protons and 16 neutrons. And hence the mass no. of oxygen is 32.
4) Calculate the number of neutrons, protons and electrons:
Ans:
Atomic number 3 and mass number 7:
Lithium is having atomic no. (Z) 3 and mass no. (A) 7.
Hence, no. of electrons = no of protons = 3
And no. of neutrons = A – Z = 7 – 3 = 4
Atomic number 92 and mass number 238.
Uranium is having atomic no. (Z) 92 and mass no. (A) 238.
Hence, no. of electrons = no of protons = 92
And no. of neutrons = A – Z = 238 – 92 = 146
5) What are nucleons? How many nucleons are present in Phosphorous? Draw its structure.
Ans: The electrons are negatively charged particles which are revolving around the positively charge nucleus due to the electrostatic force of attraction between the nucleus and the electrons. The nucleus has positive charge because it contains protons and neutrons. Protons are having positive charge while neutrons are neutral in nature. The protons and neutrons present inside the nucleus are collectively called as nucleons. The atomic no. of phosphorous is 15 that means it has 15 electrons and 15 protons. The atomic mass no. of phosphorous is 31 and hence the no. of neutrons are 16.
Thus, in phosphorous 31 nucleons are present.
VIII. Answer in detail.
1) What conclusions were made from the observations of Gold foil experiment?
Ans: In 1911, the scientist Lord Rutherford performed a famous experiment by bombarding alpha particles on the thin gold foil. He had chosen the gold because gold is the most malleable metal and he want to make a thin layer as possible.
The conclusions made from this gold foil experiment are as follows:
1) It was observed that most of the alpha particles are scattered in a straight line through the foil.
2) Some of the alpha particles get deflected from their original path of scattering.
3) And very few alpha particles are completely bounced back. From this observations Rutherford conclude that, The atom consist of a large empty space. The positively charged alpha particles get reflected and deflected from the positive charge inside the atom. And he named this positive charged space inside the atom as nucleus.
4) Also he conclude that, the volume occupied by the nucleus is very small as compared to the volume of the whole atom. From this, he find out that the radius of nucleus is 10-15 m and the radius of atom is about 10-10m.
Fig. Gold foil experimental observations
2) Explain the postulates of Bohr’s atomic model.
Ans: Neil Bohr a Danish physicist explained the stability of atom by assuming the some postulates. The postulates of Bohr’s Atomic model are as given below:
1) In an atom the electrons are revolving around the nucleus along a stationary circular paths which are called as orbits or shells or energy levels.
2) While revolving the electron in an orbit around the nucleus does not loses or gains energy.
3) When electron goes from lower to higher energy level it absorbs the energy while when the electron goes from higher energy level to lower energy level it releases the energy.
4) The orbits or shells in which electrons are revolving around the nucleus are represented by K, L, M, N….or by the numbers n= 1, 2, 3, 4…respectively.
5) The nearest orbit to the nucleus is the K shell having less energy and the electrons in it are called as K electrons.
6) And the energy of the each shell increases as the distance from nucleus increases. But the energies of the shells K, L, M …are fixed so they are also called as energy levels or energy shells.
3) State the Gay Lussac’s law of combining volumes. Explain with an illustration
Ans: Statement: According to the Gay Lussac’s law of combining volumes, whenever the gases react together, the volume of the reacting gases bear a simple ratio, and the ratio is extended to the product when the product is also in gaseous state, provided all the volumes are measured under similar conditions of temperature and pressure. This law is illustrated by using the following example: It has been experimentally proved that when two volumes of hydrogen reacts with the one volume of oxygen to form two volumes of water as shown in fig. below is the simple whole no. ratio.
Fig. one volume of hydrogen react with one volume of chlorine to give two volumes of hydrogen chloride
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