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An atom of an element  A may be written as ${}_{12}{}^{24}A$
(i) Wha does the superscript 24 indicate?
(ii) What does the subscript 12 indicate?
(iii) What are the number of protons, neutrons and electrons in an atom A?
(iv) Write the symbol of ion formed by an atom of element A.

Consider the following pairs, (i) ${}_{26}{}^{58}A, {}_{28}{}^{58}B$                (ii) ${}_{35}{}^{79}X, {}_{35}{}^{80}Y$
(a) Which of the above pairs are isotopes and isobars?
(b) What  factors are responsible for the change  in superscript, 79 80 (in case II), though the element is the same?
(c) Give the nuclear composition of ${}_{26}{}^{58}A$

What are canal rays?

If an atom contains one electron and one proton, will it carry any charge or not?

On the basis of Thomson's model of an atom, explain how the atom is neutral as a whole?

On the basis of Rutherford's model of an atom, which sub-atomic particle is present in the nucleus of an atom?

Draw a sketch of Bohr's model of an atom with three shells.

What do you think would be the observation if the $\alpha -particle$ scattering experiment is carried out using a foil of a metal other than gold?
or
Why did Rutherford select a gold foil in his $\alpha -rays$ scattering experiment?

Name the three sub-atomic particles in an atom.

Helium atom has an atomic mass of 4u and two protons in its nucleus. How many neutrons does it have?

If K and L-shells of an atom are full then what would be the total number of electrons in the atom?

How will you find the valency of chlorine, sulphur and magnesium?

If the number of electrons in an atom is 8 and the number of protons is also 8, then
(i) What is the atomic number of the atom?
(ii) What is the charge on the atom?

With the help of table given on page 92, find out the mass number of oxygen and sulphur atoms.

For the symbol H, D and T, tabulate three sub-atomic partices found in each of them.

Write the electronic configuration of any one pair of isotopes and isobars.

Compare the properties of electrons, protons and neutrons.

What are the limitation of J.J. Thomson's model of the atom?

What are the limitations of Rutherford's model of the atom ?

Describe Bohr's model of the atom.

Compare all the proposed models of an atom given in the chapter.

Define valency by taking examples of silicon and oxygen.

Explain with examples
(i) Atomic number
(ii) Mass number
(iii) Isotopes
(iv) Isobars
Give any two  uses of isotopes

$N{a}^{+}$has completely filled K and L-shells. Explain.

If bromine atom is available in the form of, say, two isotopes ${}_{35}{}^{79}Br (49.7\%) and {}_{35}{}^{81}Br (50.3\%)$, calculate the average atomic mass of bromine atom.

The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes ${}_8{}^{16}X and {}_8{}^{18}X$ in the sample?

If Z = 3 what would be the valency of the element ? Also, name the element.

Composition of the nuclei of two atomic species X and Y are given as under.
                    X    Y
Protons       6     6
Neutrons     6     8
Give the mass numbers of X and Y. What is the relation between the two species?

For the following statements, write T for true and F for false.
(i) J.J. Thomson's proposed that the nucleus of an atom contains only nucleons.
(ii) A neutron is formed by an electron and a proton combining together. Therefore, it is neutral.
(iii) The mass of an electron is about $\frac{1}{2000}$ times that of proton.
(iv) An isotope of iodine is used for making tincture of iodine, which is used as a medicine.

Rutherford's $\alpha -particle$ scattering experiment was responsible for the discovery of 
(1) atomic nucleus
(2) electron
(3) proton
(4) neutron

Isotopes of an element have
(1) the same physical properties
(2) different chemical properties
(3) different number of neutrons
(4) different atomic numbers

Number of valence electrons in $C{l}^{-}$ ion are
(1) 16
(2) 8
(3) 17
(4)_ 18

Which of the following is a correct electronic configuration of sodium?
(1) 2, 8
(2) 8, 2, 1
(3) 2, 1, 8
(4) 2, 8, 1

Complete the following table.
Atomic              Mass              Number of               Number of                Number of          Names of the 
number           number             neutrons                  protons                    electrons             atomic species
   9                       -                      10                               -                                -                           -
  16                      32                     -                                -                                -                         Sulphur
   -                        24                     -                               12                              -                            -
   -                         2                      -                                 1                              -                            -
   -                         1                      0                                 1                              0                           -           

Then first model of an atom was given by
(1) N Bohr
(2) E Goldstein
(3) Rutherford
(4) JJ Thomson

Which of the following statements about Rutherford's model of an atom are correct?
(i) Considered the nucleus as positively charged
(ii) Established that the $\alpha -particles$ are four times as heavy as a hydrogen atom
(iii) Can be compared to solar system
(iv) Was in agreement with Thomson's model
(1) (i) and (iii)
(2) (ii) and (iii)
(3) (i) and (iv)
(4) only (i)

Which class is nearest to the nucleus of an atom?
(1) K-class (shell)
(2) L-class (shell)
(3) M-class (shell)
(4) N-class (shell)

Who discovered neutron?
(1) J. Chadwick
(2) Dalton
(3) Bohr
(4) Rutherford

The electron distribution in an aluminium atom is
(1) 2, 8, 3
(2) 2, 8, 2
(3) 8, 2, 3
(4) 2, 3, 8

Which one of the following element has 2, 8, 8, 2 electronic configuration?
(1) Calcium
(2) Copper
(3) Silver
(4) Palladium

Identify the $M{g}^{2+}$ ion from the figure where, n and p represent the number of neutrons and protons respectively.
(1)
 
(2)

(3)

(4)

Which of the following is the valency of an element, if it has 2, 8, 2 electronic configuration?
(1) 2             (2) 4            (3) 6          (4) 0

An atom with 3 protons and 4 neutrons will have a valency of 
(1) 3          (2) 7          (3) 1              (4) 4

${}_{1}H^1$ is named as
(1) protium
(2) deuterium
(3)tritium
(4) proton

Assertion Cathode rays get deflected towards the positive plate of electric field.
Reason Cathode rays consist of negatively charged particles known as electrons.
(1) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(2) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(3) If Assertion is true but Reason is false.
(4) If Assertion is false and Reason is true.
(5) If both Assertion and Reason are false.

Assertion  In Rutherford's gold foil experiment, very few $\alpha$-particles are deflected back.
Reason Nucleus present inside the atom is heavy.
(1) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(2) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(3) If Assertion is true but Reason is false.
(4) If Assertion is false and Reason is true.
(5) If both Assertion and Reason are false.

Assertion Electronic configuration of neon is 2, 8
Reason Atomic number of neon is 8
(1) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(2) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(3) If Assertion is true but Reason is false.
(4) If Assertion is false and Reason is true.
(5) If both Assertion and Reason are false.

Assertion The atoms of different elements having same mass number but different atomic number are known as isobars.
Reason The sum of protons and neutrons, in the isobars is always different.
(1) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(2) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(3) If Assertion is true but Reason is false.
(4) If Assertion is false and Reason is true.
(5) If both Assertion and Reason are false.

Assertion  Mass number of an atom of calcium is 38.
Reason The number of protons and number of neutrons present in an atom of calcium are 19 and 19 respectively.
(1) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(2) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(3) If Assertion is true but Reason is false.
(4) If both Assertion and Reason are false.

Which scientist concluded that size of nucleus is very small as compared to size of an atom?

One electron is present in the outermost shell of the atom of an element X. What would be the nature and value of charge on the ion formed if this electron is removed from the outermost shell ?

In the atom of an element X, 6 electrons are present in the outermost shell. If it acquires noble gas configuration by accepting requisite number of electron, then what would be the charge on the ion so formed.

What is the atomic number of the atom of an element X, which has 2 shells, K and L having 2 and 6 electrons respectively?

What is the difference between Na and $N{a}^{+}$ in terms of number of electrons?

Write the mass number of neon and argon from the data given below.
Element            Number of Protons             Number of Neutrons
Neon                           10                                       10
Argon                          18                                        22

Calculate the number of neutrons present in the nucleus of an element X which is represented as ${}_{15}{}^{31}X$.

Identify the pair of isotopes from the following:
${}_8{}^{16}X, {}_7{}^{16}X, {}_8{}^{17}X$

The atomic number of calcium and argon are 20 and 18 respectively but the mass number of both these elements is 40. What is the name given to such a pair of elements?

Which of the two would be chemically more reactive: element A with atomic number 18 or element D with atomic number 16 and why?

 
which isotope of hydrogen contain same number of electrons, protons and neutrons?

How can you justify that cathode-rays originate from the cathode whereas anode rays do not?

Write the conclusions drawn by Rutherford when he observed the following.
(i) Most of the $\alpha -$particles passing straight through the gold foil.
(ii) Some $\alpha -$particles getting deflected from their path.
(iii) Very small fraction of $\alpha -$particles getting deflected by $180°$

List down three different names given to the path in which electrons revolve around the nucleus. Also, explain why are they called so?

(i) What will be the maximum number of electrons which can be filled in Z-shell of an imaginary atomic model?
(ii) Why is it almost impossible to find such an atom in nature?
 

Atomic number of aluminium is 13 and mass number is 27. Calculate the number of electrons, protons and neutrons in its atom. Represent the ion of this element.

(i) Write the name of an element whose atom has same number of sub-atomic particles. Draw the atomic structure of the atom.
(ii) Draw atomic structure of an atom with same number of  electrons in L and M-shells.

Given below is the atomic structure of an atom of element ${}_{11}{}^{23}A$, according to Bohr's model of atom.

(i) What is wrong with this structure of atom?
(ii) Draw a correct representation  of this atom.
(iii) Write the chemical formula of the chloride of this element.

Write the electronic configuration and valency of the following.
(i) Chlorine
(ii) Sodium
(iii) Silicon

Write the electronic configurations for the following elements and deduce their valencies.
(i) Magnesium     (ii) Neon        (iii) Sulphur

Find out the valency of atoms represented by the following figures.

The following data represents the distribution of electrons, protons and neutrons in atoms of four elements A, B, C, D.
Element              Protons                Neutrons                Electrons
    A                          10                          10                            10
    B                          11                           12                            11
    C                          12                           12                            12
    D                          13                           14                            13
Solve the following questions.
(i) Write the electronic distribution of atoms of element A and D.
(ii) Element A is an inert gas. Why ?
(iii) What is the valency of element C?

You are given the atom of an element ${}_8{}^{16}X$. Find out the
(i) Number of protons, electrons adn neutrons in X.
(ii) Valency of X.
(iii) Chemical formula of the compound formed when X reacts with
(a) hydrogen           (b) carbon

An atom of an element has 5 electrons in L-shell.
(i) What is the atomic number of the element?
(ii) State its valency.
(iii) Identify the element and write its name.

(i) Answer the following questions
(a) Name the scientist who discovered protons.
(b) What is the charge and mass on a proton?
(c) Where is proton located in an atom?
(ii) An atom of an element has mass number 28 u and its atomic number is 14. How many neutrons does it have ? Also, name the element.

Show diagramatially the electron distributions in a sodium atom and  a sodium ion and also give their atomic number.

An atom of an element has two electrons in the outermost M-shell. State
(i) electronic configuration
(ii) atomic number
(iii) number of protons
(iv) valency of this element

What information do you get from the figure about the atomic number, mass number and valency of atom X, Y and Z? Give your answer in a tabular form.

Complete the table on the basis of information available in the symbols given below.
(i) ${}_{17}{}^{35}Cl$              (ii) ${}_6{}^{12}C$          (iii) ${}_{35}{}^{81}Br$
Element       $n_p$         $n_n$

Complete the following table.
Element        Atomic Number      Protons       Electrons         Neutrons         Mass Number
     A                       17                                               17                    18
     B                                                   14                   14                    14                          
     C                                                    9                     9                                                 19

In the following table the mass numbers and the atomic numbers of certain elements are given. 
Element     A           B          C         D           E
Mass no.    1           7          14        40         40
At. no.         1          3           7         18          20
(i) Select a pair of isobars from the above table.
(ii) What would be the valency of element C listed in the above table?
(iii) Which two sub-atomic particles are equal in number in a neutral atom?

Two elements are represented as ${}_{17}X^{35} and {}_{12}Y^{24}$.
(i) Which of these elements will lose and gain electrons?
(ii) What is the number of electrons an atom loses, gains or shares called?
(iii) Write the electronic configurations of X and Y.

A metal (mass number = 40) having same number of protons and neutrons, combines with two chlorine atoms. Identify the element with which electronic configuration of this metal matches in combined state.

In response to a question, a student stated that in an atom, the number of protons is greater than the number of neutrons, which in turn is greater than the number of electrons. Do you agree with the statement? Justify your answer.

An ion $M^{3-}$ contains 10 electrons and 7 neutrons. What is the atomic number and mass number of the element M? Name the element.

Sulphur dioxide$\left(S{O}_2\right)$ is a  colourless pungent smelling gas and is a major air pollutant.
(i) Write the electronic configuration of its constituent elements 'sulphur and oxygen' (Given ${}_{16}{}^{32}S, {}_8{}^{16}O$).
(ii) Write the valency of sulphur and oxygen.
(iii) Are sulphur and oxygen isotopes of same element? Explain your answer.

Study the data given below and answer the questions which follows:
Particle          Electrons              protons           Neutrons
     A                      2                          3                        4
     B                     10                         9                        8
     C                      8                          8                        8
     D                      8                          8                       10
(i) Write the mass number and atomic number of particles A, B, C, D.
(ii) Which particles represent a pair of isotopes? Explain.

The two isotopes of chlorine have mass number 35 and 37 and number of neutrons 18 to 20 respectively. Which one will have higher valency? Do they have same physical or chemical properties? 

(i) What is the number of electrons in $C{l}^{-}$ ion (Cl = 17)?
(ii) What is the electronic configuration of phosphorus (P = 15)?
(iii) Which isotope of uranium is used in nuclear fuel?

An element M forms the compound $M{H}_3$ when it reacts with hydrogen.
(i) Find the valency of element M.
(ii) Write the valency of chlorine and sulphur.
(iii) Name three isotopes of hydrogen.

(i) Identify which of the following pairs are isotopes and which are isobars ? Give reasons for your choice.
${}^{58}A_{26}, {}^{58}B_{28}, {}^{79}X_{35}, {}^{80}Y_{35}$
(ii) Do isobars also have identical chemical properties like isotopes? State reason.

(i) Chlorine occurs in nature in two isotopic forms with masses 35 u and 37 u. The percentage of ${}^{35}Cl$ is 75%. Find the average atomic mass of chlorine atom.
(ii) Give any three applications of isotopes.

On the basis of the number of protons, neutrons and electrons in the samples given below identify
(i) the cation
(ii) the pair of isobars, and
(iii) the pair of isotopes
Sample             Protons            Neutrons            Electrons
    A                        17                     18                          16
    B                        18                     19                          18
    C                        17                     20                          17
    D                        17                     17                          17
 

In the gold foil experiment of Geiger and Marsden, that paved the way for Rutherford's model of an atom, -1.00% of the $\alpha$-particles were found to deflect at angles greater than $50°$. If one mole of $\alpha$-particles were bombarded on the gold foil, compute the number of $\alpha$-particles that would deflect at angles less than $50°$

If the mass of a proton is 1.67$\times {10}^{-27}$ kg and if electron is found to be 1840 times lighter than hydrogen ion. Then find the charge to mass ratio of cathode rays. [Given, charge on 1 electron = 1.6$\times {10}^{-19}C$]

Two ions having 3 negative and 3 positive charges are found to have 7 and 14 neutrons respectively. If electronic configuration of these ions are similar to that of neon (Ne), then find the mass number of both the ions.

(i) Why do isotopes of an element show similar chemical properties?
(ii) How did Rutherford come to the conclusion that most of the space in an atom is empty?

(i) Which popular experiment is shown in the figure?
(ii) List three observations of this experiment
(iii) State conclusions drawn from each observation of this experiment.
(iv) State the model of the atom suggested on the basis of the experiment.

(i) What is an octet? How do elements attain an octet?
(ii) Make a schematic atomic structure of  magnesium and phosphorus.
[Given number of protons of magnesium = 12 and that of phosphorus = 15]

(i) An element X has an atomic number = 12 and mass number = 26. Draw a diagram showing the distribution of electrons in the orbits and the nuclear composition of the neutral atom of the element. What is the valency of the element and why?
(ii) If this element X combines with another element Y whose electronic configuration is 2, 8, 7. What will be the formula of the compound thus formed? State how did you arrive at this formula.

(i) From Rutherford's $\alpha$-particle scattering experiment, give the experimental evidence for deriving the conclusion that 
(a) most of the space inside the atom is empty.
(b) the nucleus of an atom is positively charged.
(ii) An element has mass number = 32 and atomic number = 16, find 
(a) the number of neutrons in the atom of the element.
(b) the number of electrons in the outermost shell of the atom.
(iii) On the basis of Rutherford's model of an atom, which subatomic particle is present in the nucleus of an atom?

(i) Write two differences between isotopes and isobars.
(ii) Write uses of Co-60 and U-235.

Number of electrons, protons and neutrons in chemical species A, B, C and D is given below.
Chemical species              Electrons         Protons              Neutrons
              A                                   2                      3                           4
              B                                  10                     9                            8
              C                                   8                      8                            8
              D                                   8                      8                            10
Now answer the following questions.
(i) What is the mass number of A and B?
(ii) What is the atomic number of B?
(iii) Which two chemical species represent a pair of isotopes and why?
(iv) What is the valency of element C?
      Also justify your answers.

The cathode ray experiment was done for the first time by
(1) Goldstein
(2) J.J Thomson
(3) Dalton
(4) Rutherford

How many neutrons are present in the nucleus of hydrogen atom?
(1) 1
(2) 2
(3) 3
(4) 0

Which of the following correctly represent the electronic distribution in the Mg atom?
(1) 3, 8, 1
(2) 2, 8, 2
(3) 1, 8, 3
(4) 8, 2, 2

Number of valence electrons present in $N^{3-}$ ion is 
(1) 16
(2) 10
(3) 7
(4) 4

The number of electrons in an element X is 15 and the number of neutron is 16. Which of the following is the correct representation of the element?
(1) ${}_{15}{}^{31}X$
(2) ${}_{16}{}^{31}X$
(3) ${}_{15}{}^{16}X$
(4) ${}_{16}{}^{15}X$

Assertion The valency of an atom of flourine is 7.
Reason The number of electrons present in the outermost shell of an atom are known as the valence electrons.
(1) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(2) If both Assertion and Reason are true but Reason is not te correct explanation Assertion.
(3) If Assertion is true but Reason is false.
(4) If Assertion is false but Reason is true.
(5) If both Assertion and Reason are false.

Assertion Bohr's orbits are called stationary orbits.
Reason Electron remain stationary in these orbits for some time.
(1) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(2) If both Assertion and Reason are true but Reason is not the correct explanation Assertion.
(3) If Assertion is true but Reason is false.
(4) If Assertion is false but Reason is true.
(5) If both Assertion and Reason are false.

Assertion According to Bohr's model, the orbits of an atom are also called energy levels.
Reason Orbits are the spheres containing define value of energy.
(1) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(2) If both Assertion and Reason are true but Reason is not the correct explanation Assertion.
(3) If Assertion is true but Reason is false.
(4) If Assertion is false but Reason is true.
(5) If both Assertion and Reason are false.

In the Thomson's model of atom, which of the following statements are correct?
(i) The mass of the atom is assumed to be uniformly distributed over the atom.
(ii) The positive charge is assumed to be uniformly distributed over the atom.
(iii) The electrons are uniformly distributed in the positively charged sphere.
(iv) The electrons attract each other to stabilise the atom.
(1) (i), (ii) and (iii)
(2) (i) and (iii)
(3) (i) and (iv)
(4) (i), (iii) and (iv)

The atomic number of an element is 13 and its mass, mass nubmer is 27. The correct order representing the number of electrons, protons and neutrons respectively in this atom is
(1) 13, 13, 14
(2) 14, 13, 13
(3) 27, 13, 13
(4) 27, 14, 13

The following diagram depicts the Rutherford's experiment.

why was zinc sulphide screen is used in the experiment?
(1) To block $\alpha$-particles from going straight
(2) To detect deflection of $\alpha$-particles
(3) To further deflect $\alpha$-particles as the gold foil did.
(4) To absorb $\alpha$-particles and utilise it again