# Samacheer Kalvi Class 8 Science Unit 12 Atomic Structure Solutions

## Samacheer Kalvi Class 8 Science Unit 12 Atomic Structure Solutions

Welcome to NCTB Solutions. Here with this post we are going to help 8th class students by providing Solutions for Samacheer Kalvi Class 8 Science Unit 12 Atomic Structure. Here students can easily find all the solved solution for Atomic Structure Exercise questions. Also here our Expert Science Teacher’s solved all the questions with easily understandable language with proper guidance so that all the students can understand easily. Here on this post students will get Unit 12 Atomic Structure exercise solutions. Here all the solutions are based on Tamil Nadu State Board latest syllabus.

#### Unit 12 Atomic Structure Exercise Questions Solutions :

(1) The same proportion of carbon and oxygen in the carbon dioxide obtained from different sources proves the law of

(a) Reciprocal proportion

(b) Definite proportion

(c) Multiple proportions

(d) Conservation

Correct Option → (b)

The same proportion of carbon and oxygen in the carbon dioxide obtained from different sources proves the law of Definite proportion.

(2) Cathode rays are made up of ___

(a) Natural particles

(b) Positively charged particles

(c) Negatively charged particles

(d) None of the above

Correct Option → (c)

Cathode rays are made up of Negatively charged particles.

(3) In water, hydrogen and oxygen are combined in the ratio of ___ by mass

(a) 1 : 8

(b) 8 : 1

(c) 2 : 3

(d) 1 : 3

Correct Option → (a)

In water, hydrogen and oxygen are combined in the ratio of 1 : 8 by mass.

(4) Which of the following statements made by Dalton has not any change

(a) Atoms cannot be broken

(b) Atoms combine in small, whole numbers to form compounds

(c) Elements are made of atoms

(d) All atoms of an elements are alike

Correct Option → (d)

All atoms of an elements are alike” – This statement is made by Dalton has not any change.

(5) In all atoms of an element

(a) The atomic and the mass number are same

(b) The mass number is same and the atomic number is different.

(c) The atomic number is same and the mass number is different

(d) Both atomic and mass numbers may vary.

Correct Option → (d)

In all atoms of an element Both atomic and mass numbers may vary.

(II) Fill in the blanks

(1) __ is the smallest particle of an element.

(2) An element is composed of __ atoms.

(3) An atom is made up of __ ,__ and __

(4) A negatively charged ion is called __ while positively charged ion is called __

(5) __ is a negatively charged particle (Electron/Proton).

(6) Proton is deflected towards the __ charged plate (positively, negatively).

(1) →  Atoms

(2) →  Small atoms

(3) →  Proton, neutrons and electrons.

(4) →  Anions, cations

(5) →  Electron

(6) →  Positively

(1) State the law of conservation of mass.

Conservation of mass states that in a chemical reaction, the matter cannot be created nor destroyed. It can only change form one form to another form of matter.

(2) State the law of constant proportions.

The law of constant of proportion is sates that, in a pure chemical compound the elements are always present in definite proportion by mass.

(3) Write the properties of anode rays.

Properties of anode rays :

(a) Anode rays travel in straight lines.

(b) Anode rays are made up of material particles

(c) Anode rays are deflected by electric and magnetic fields and they are deflected towards negatively charged particles.

(d) The properties of anode rays depends upon the nature of the gas taken inside in the discharge tube.

(4) Define valency of an element with respect to hydrogen.

The combining capacity of an atom is known as valency . the valency of the hydrogen can be defined as the number of hydrogen atom combine with one atom of it. Valency of hydrogen atom is one.

(5) Define the term ions or radicals.

An atoms or the group of an atoms when they either lose or gain electrons are known as ions or radicals. There are two types of ions or radicals anions and cations.

(6) What is a chemical equation?

Chemical equation is a short hand representation n of a chemical reactions with the help of chemical symbols and formulae. Chemical equation has reactant and product.

(7) Write the names of the following compounds.

(a) CO

(b) N2O

(c) NO2

(d) PCl5

(a) CO → Carbon monoxide

(b) N2O → Nitrous oxide

(c) NO2 → Nitrogen dioxide

(d) PCl5 → Phosphorus pent chloride.

(1) Find the valency of the element which is underlined in the following formula.

(a) NaCl

(b) CO2

(c) Al (PO4)

(d) Ba (NO3)2

(e) CaCl2

The valency of the following elements are as follows –

Elements – Valency

NaCl – Na – valency is +1

CO2 – C – valency is 0

Al(PO)4 – Al – valency is +3

Ba( NO3)2 – Ba – valency is +2

CaCl2 – Ca – valency is +2

(2) Write the chemical formula for the following compounds

(a) Aluminium sulphate

(b) Silver nitrate

(c) Magnesium oxide

(d) Barium chloride

 Compounds : Chemical formula : Aluminium sulfate Al2( SO4)3 Silver nitrate AgNO3 Magnesium oxide MgO Barium chloride BaCl2

(VI) Higher Order Thinking Questions.

(1) Why does a light paddle wheel placed in the path of cathode rays begin to rotate, hen cathode rays fall on it?