# Maharashtra Board Class 8 Science Chapter 5 Inside the Atom Solution

## Maharashtra Board Class 8 Science Solution Chapter 5 – Inside the Atom

Balbharati Maharashtra Board Class 8 Science Solution Chapter 5: Inside the Atom. Marathi or English Medium Students of Class 8 get here Inside the Atom  full Exercise Solution.

 Std Maharashtra Class 8 Subject General Science Solution Chapter Inside the Atom

(a.)  What is the difference in the atomic models of Thomson and Rutherford?

Ans. The difference between atomic models of Thomson and Rutherford:

 Thomson Model Rutherford Model (i) It assumes that atom is a sphere of positive charge in which negative charged particles are  studded. So positive charge & mass is distributed evenly. (i) It assumes that all the positive charge and almost all mass is concentrated in a very small space called nucleus. (ii) This model is called by ‘Plum pudding model’. (ii) This model is called by ‘nuclear model’. (iii) This model does not contain any details about nucleus. (iii) This model explains about nucleus. (iv) It is discover in 1904. (iv) It is discover in 1909.

b.) What is meant by valency of an element? What is the relationship between the number of valence electron and valency?

Ans. Valency of element:- The valency of an element is the tendency of its atoms to attempt to gain or to donate a certain number of elements in its outer shell. Valency is the combining capacity of an element. Those that are trying to gain electrons tend to be non-metals and those that tend to donate electrons tend to be metals.

The relationship between the number of valence electron and valency:-

Valence electron is the total number of electrons prese not in the outermost shell of an atom.

Valency is the number of electrons an atom loses, gain or shears with other atom so as to complete the shell.

Ex: Valency os nitrogen is ‘3’. It need 3 more electron, then valence electrons is 5.

c.) What is meant by atomic mass number ? Explain how the atomic number and mass number of carbon are 6 and 12 respectively.

Atomic mass number:- In an atomic neutrons the total number of protons & neutrons which together known as nucleous is called as Atomic mass number. It is typically expressed in atomic mass units.

mass number = Proton + neutrons.

The atomic number of Carbon is 6:-

The atomic number of carbon ‘6’ due to electron configuration. We know that, atomic number is proton number os an atom. Carbon’s proton’s number are 6. So atomic number of carbon is ‘6’.

The atomic mass number of carbon is 12:-

Due to electron configuration the atomic mass number of carbon is ’12’. We know atomic mass number = Proton + neutron. In the carbon atomic structure proton is ‘6’ & neutron is ‘6’. So 6 + 6 = 12 is atomic mass number of carbon.

d.) What is meant by subatomic particle ? Give brief information of three subatomic particles with reference to electrical charge, mass and location.

Ans. Subatomic Particle:- A typical atom consists of three subatomic particles : Protons, Electrons & Neutrons. It is smaller then atom. It is a unit of matter or energy.

 Proton Neutron Electron Electrical charge a positive charge symbol p+, with a positive electric charge of +1e It is neutral. Symbol n or no. a negative charge. electric charge is -1.602 x 10-19C. Mass 1.67262 x 10-27 kg 1.67293 x 10-27 kg 9.1093837015 x 10-31 kg. Location inside the nucleus inside the nucleus Outside the electron.

(2.) Give scientific reasons.

a.) All the mass of an atom is concentrated in the nucleus.

Ans. We know that, a atom contains mainly three subatomic particles; electron, proton & neutron. Its means, mass of an atom = mass of proton + mass of neutrons. Electron revolves around the nucleus in the orbit while proton & neutron are located at the catre os the atom, their catre is known as nucleus. We know, mass of electro is comparably negligible than mass of proton & that of neutron.

Therefore, we can say, all mass of an atom is concentrated in the nucleus.

b.) Atom is electrically neutral.

Ans. Atoms are electrically neutral because they have equal numbers of proton (positive charges) & electrons (negatively charges). If an atom gains or loses one or more electrons, it becomes on ion. If it gains one or more electrons, it now carries a net negative charge, & is thus ‘anionic’.

c.) Atomic mass number is a whole number

Ans. We know that atomic mass number is the sum of the number of protons & neutrons of a atomic nucleus. It is the sum of the number of nucleus in a atom. So, we can say atomic mass number is a whole number.

d.) Atoms are stable though negatively charged electron are revolving within it.

Ans. Atom exist three subatomic particles; proton, electron & neutron. Proton is positively charges & electron has negative charged. In an atom the number of protons is equal to the number of electrons. Due to same number of protons & neutrons atom are neutralised. So atom are stable through negatively charged electron are revolving within it.

(3.) Define the following terms

a) Atom:- An atom is smallest particle of matter. An atom is the smallest particle of an element which retains its chemical identity in all the physical & chemical changes.

b) Isotope:- The atomic number is a fundamental property of an element & its chemical identity. Atom of some element having different mass number are called Isotops.

c) Atomic number:- Atomic number is electron configuration. The proton numbers of atom is known as atomic number.

d) Atomic mass number:- In an Atom the sum of protons & electrons are known as atomic mass number. It is denoted by ‘A’. A = P + Z.

e) Moderator in nuclear reactor:- The moderator is used as thermal reactor, used to moderate.

(4.) Draw a neat labelled diagram.

a.)  Ruthrford’s scattering experiment

b.) Thomson’s atomic model

c.) Diagramatic sketch of electronic configuration of Magnesium (Atomic number 12)

d) Diagramatic sketch of electronic configuration of Argon (Atomic number 18)

Solution:  (5.) Fill in the blanks.

a.) Electron, proton, neutron are the types of ______ in an atom.

Ans. Subatomic particles.

b.) An electron carries a ______ charge.

Ans. Negative.

c.) The electron shell ______ is nearest to the nucleus.

Ans. K

d.) The electronic configuration of magnesium is 2, 8, 2. From this it is understood that the valence shell of Magnesium is _______.

Ans. 2

e.) The valency of hydrogen is ‘one’ as per the molecular formula H2O. Therefore valency of ‘Fe’ turns out to be _______ as per the formula Fe2O3

Ans. 3

(6.) Match the pairs.

 Group A Group B a. Proton i. Negatively charged b. Electron ii. Neutral c. Neutron iii. Positively Charged

Ans.

 Group A Group B a. Proton iii. Positively Charged b. Electron i. Negatively charged c. Neutron ii. Neutral

(7.) Deduce from the datum provided Updated: May 3, 2020 — 10:00 pm