STRUCTURE OF THE ATOM

In the Gold foil experiment of Geiger and Marsden, that paved the way for
Rutherford’s model of an atom, ~ 1.00% of the a-particles were found to
deflect at angles > 50º. If one mole of a-particles were bombarded on the
gold foil, compute the number of a-particles that would deflect at angles
less than 500.

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

In what way is the Rutherford’s atomic model different from that of
Thomson’s atomic model?

Enlist the conclusions drawn by Rutherford from his a-ray scattering
experiment.

Why do Helium, Neon and Argon have a zero valency?

An element X has a mass number 4 and atomic number 2. Write the valency
of this element?

Fill in the blanks in the following statements
(a) Rutherford’s a-particle scattering experiment led to the discovery of
the ———
(b) Isotopes have same ———but different———.
(c) Neon and chlorine have atomic numbers 10 and 17 respectively. Their
valencies will be———and———respectively.
(d) The electronic configuration of silicon is ———and that of sulphur
is ———.

Helium atom has 2 electrons in its valence shell but its valency is not 2,
Explain.

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?

Match the names of the Scientists given in column A with their contributions
towards the understanding of the atomic structure as given in column B
(A)                                                (B)
(a) Ernest Rutherford                       (i) Indivisibility of atoms
(b) J.J.Thomson                               (ii) Stationary orbits
(c) Dalton                                        (iii) Concept of nucleus
(d) Neils Bohr                                   (iv) Discovery of electrons
(e) James Chadwick                           (v) Atomic number
(f) E. Goldstein                                  (vi) Neutron
(g) Mosley                                         (vii) Canal rays

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.

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
electrons, then what would be the charge on the ion so formed?

Write down the electron distribution of chlorine atom. How many electrons
are there in the L shell? (Atomic number of chlorine is 17).

One electron is present in the outer most 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 outer most shell?

Why did Rutherford select a gold foil in his a–ray scattering experiment?

Write any two observations which support the fact that atoms are divisible.

Is it possible for the atom of an element to have one electron, one proton
and no neutron. If so, name the element.

Complete the following table.

Which one of the following is a correct electronic configuration of sodium?

(a) 2, 8

(b) 8, 2, 1

(c) 2, 1, 8

(d) 2, 8, 1

Put tick () against correct choice and cross () against wrong choice in the following question:

Number of valence electrons in Cl - 'ion are:

(a) 16

(b) 8

(c) 17

(d) 18

Put tick () against correct choice and cross () against wrong choice in the following question:

Isotopes of an element have

(a) the same physical properties

(b) different chemical properties

(c) different number of neutrons

(d) different atomic numbers

Put tick () against correct choice and cross () against wrong choice in the following question:

Rutherford's alpha-particle scattering experiment was responsible for the discovery of

(a) Atomic nucleus

(b) Electron

(c) Proton

(d) Neutron

For the following statements, write T for 'True' and F for 'False'.

(a) J.J. Thomson proposed that the nucleus of an atom contains only nucleons.

(b) A neutron is formed by an electron and a proton combining together. Therefore, it is neutral.

(c) The mass of an electron is about times that of proton.

(d) An isotope of iodine is used for making tincture iodine, which is used as a medicine.

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

The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes  and  in the sample?

 If bromine atom is available in the form of, say, two isotopes  (49.7%) and  (50.3%), calculate the average atomic mass of bromine atom.

Na+ has completely filled K and L shells. Explain.

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

Define valency by taking examples of silicon and oxygen.

Summarize the rules for writing of distribution of electrons in various shells for the first eighteen elements.

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

Describe Bohr's model of the atom.

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

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

Compare the properties of electrons, protons and neutrons.

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

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

With the help of Table 4.1, find out the mass number of oxygen and sulphur atom.

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

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

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

Write the distribution of electrons in carbon and sodium atoms?

What do you think would be the observation if the α particle scattering experiment is carried out using a foil of a metal other than gold?

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

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

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

Name the three sub-atomic particles of an atom.

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

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

What are canal rays?