If bromine atom is available in the form of two isotopes Br 35 79 49 % and Br 35 81 51 % . Calculate the average atomic mass of the bromine atom.

The atoms of the same element having the same atomic number, but different mass numbers are called isotopes of the element. Here given, the availability of bromine isotopes are: Br 35 79 = 49 % and Br 35 81 = 51 % Hence, the average atomic mass of bromine atoms on the basis of the above data will be: 79 × 49 100 + 81 × 51 100 = 38 . 71 + 41 . 31 = 80 . 2 u .

The composition of the nuclei of two atomic species X and Y are as follows: X Y No. of protons 15 15 No. of neutrons 15 16 Give the mass numbers of X and Y . What is the relation between the two species?

The sum of the number of protons and neutrons present in the nucleus of an atom is called the mass number. Thus, the relationship between proton number, mass number and the number of neutrons in an atom can be given as follows: Mass number = No. of protons + No. of neutrons Therefore, the mass number of X is = 15 + 15 = 30 The mass number of Y is = 15 + 16 = 31 Both X and Y have an equal number of protons, that is 15 , but different mass numbers 30 and 31 respectively. So, they are isotopes. The atoms of the same element having the same atomic number, but different mass numbers are called isotopes of the element.

Complete the following table: Atomic number Mass number Number of protons Number of neutrons Number of electrons Name of the atomic species 11 _____ _____ 12 _____ _____ _____ _____ 11 12 10 _____ 17 35 _____ _____ _____ _____ 17 35 _____ _____ 18 _____ _____ 27 13 _____ _____ _____

Atomic number Mass number Number of protons Number of neutrons Number of electrons Name of the atomic species 11 23 11 12 11 Sodium 11 23 11 12 10 Sodium ion Na + 17 35 17 18 17 Chlorine 17 35 17 18 18 Chloride ion Cl - 13 27 13 14 13 Aluminium The atomic number is the number of protons in the nucleus of an atom. Since the atom, on the whole, is neutral, the number of protons in the nucleus is equal to the number of electrons outside the nucleus. The sum of the number of protons and neutrons present in the nucleus of an atom is called the mass number. Thus, the relationship between atomic number, mass number and number of neutrons in an atom can be given as follows: Mass number = No. of protons or atomic number + No. of neutrons.

E M B I B E

Science for Class 9>Chapter 5 - Structure of the Atom>EXERCISES

Manipur Board Solutions for Chapter: Structure of the Atom, Exercise 5: EXERCISES

Author:Manipur Board

Manipur Board Science Solutions for Exercise - Manipur Board Solutions for Chapter: Structure of the Atom, Exercise 5: EXERCISES

Attempt the practice questions on Chapter 5: Structure of the Atom, Exercise 5: EXERCISES with hints and solutions to strengthen your understanding. Science for Class 9 solutions are prepared by Experienced Embibe Experts.

Questions from Manipur Board Solutions for Chapter: Structure of the Atom, Exercise 5: EXERCISES with Hints & Solutions

HARD

9th Manipur Board

IMPORTANT

Science for Class 9>Chapter 5 - Structure of the Atom>EXERCISES>Q 6

The mass number of an element is $40$ . It contains $19$ electrons. What is the number of protons and neutrons in it? What is the atomic number of the element?

EASY

9th Manipur Board

IMPORTANT

Science for Class 9>Chapter 5 - Structure of the Atom>EXERCISES>Q 7

Write the electronic configuration of the potassium atom: $(Z = 19)$ .

HARD

9th Manipur Board

IMPORTANT

Science for Class 9>Chapter 5 - Structure of the Atom>EXERCISES>Q 8

Explain why, sodium ion, ${Na}^{+}$ , has completely filled $K$ and $L$ shells.

MEDIUM

9th Manipur Board

IMPORTANT

Science for Class 9>Chapter 5 - Structure of the Atom>EXERCISES>Q 9

If both $K$ and $L$ shells of an atom are full, what is the total number of electrons in the atom?

MEDIUM

9th Manipur Board

IMPORTANT

Science for Class 9>Chapter 5 - Structure of the Atom>EXERCISES>Q 10

If bromine atom is available in the form of two isotopes ${}_{35}^{79}{Br} (49 %) and {}_{35}^{81}{Br} (51 %)$ . Calculate the average atomic mass of the bromine atom.

HARD

9th Manipur Board

IMPORTANT

Science for Class 9>Chapter 5 - Structure of the Atom>EXERCISES>Q 11

The composition of the nuclei of two atomic species $X$ and $Y$ are as follows:

	$X$	$Y$
No. of protons	$15$	$15$
No. of neutrons	$15$	$16$

Give the mass numbers of $X$ and $Y$ . What is the relation between the two species?

HARD

9th Manipur Board

IMPORTANT

Science for Class 9>Chapter 5 - Structure of the Atom>EXERCISES>Q 12

What is the relation between the valency of an element and the number of valence electrons in its atom? Explain with examples.

HARD

9th Manipur Board

IMPORTANT

Science for Class 9>Chapter 5 - Structure of the Atom>EXERCISES>Q 13

Complete the following table:

Atomic number	Mass number	Number of protons	Number of neutrons	Number of electrons	Name of the atomic species
$11$	_____	_____	$12$	_____	_____
_____	_____	$11$	$12$	$10$	_____
$17$	$35$	_____	_____	_____	_____
$17$	$35$	_____	_____	$18$	_____
_____	$27$	$13$	_____	_____	_____

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