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Standard IX

Chemistry

Rutherford's model of an atom

What did Ruth...

Question

What did Rutherford conclude regarding the atomic mass?
(i) Mass of the atom is uniformly distributed.
(ii) Nucleus of an atom is much heavier than electron.
(iii) Nearly all the mass of an atom resides at the centre of an atom.
(iv) Nucleus of an atom is lighter than the electron.

Both (i) and (ii)

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Both (i) and (iv)

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Both (ii) and (iii)

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Both (iii) and (iv)

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Solution

The correct option is C
Both (ii) and (iii)

According to Rutherford experiments, a very small fraction of α-particles were deflected by 180⁰, indicating that all the positive charge and mass of the gold atom were concentrated in a very small volume within the atom. This proves that there is a positively charged centre in the atom called nucleus. Nearly all the mass of an atom resides in the nucleus. It is not uniformly distributed throughout the atom. This also proves that mass of nucleus is much larger than mass of electron.

Mass of atom = mass of nucleus + mass of electrons, where mass of nucleus >> mass of electron.

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Similar questions

During Rutherford's α-particle scattering experiment, he concluded that:

(i) electrons have a negative charge.
(ii) the mass and positive charge of the atom is concentrated in the nucleus.
(iii) neutron exists in the nucleus.
(iv) most of the space in an atom is empty.

Multiple Choice Questions

(a) The outermost shell of an atom is known as

(i) valency

(ii) valence electrons

(iii) nucleus

(iv) valence shell

(b) The number of valence electrons present in magnesium is

(i) two

(ii) three

(iii) four

(iv) five

(i) proton

(ii) neutron

(iii) electron

(iv) nucleon

(d) If the atomic number of an atom is 17 and mass number is 35 then number of neutrons will be

(i) 35

(ii) 17

(iii) 18

(iv) 52

(e) The number of electrons in an atom is equal to the number of

(i) protons in a neutral atom

(ii) neutrons in a neutral atom

(iii) nucleons in a neutral atom

(iv) none of the above

(f) The sum of number of protons and number of neutrons present in the nucleus of an atom is called its

(i) mass number

(ii) atomic number

(iii) number of electrons

(iv) all of the above

In Thomson’s model of an 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 stabilize the atom.

Q. An atom of an element contains

13

electrons. Its nucleus has

14

neutrons. Find out its atomic number and approximate atomic mass. An isotope has atomic mass

2

units higher. What will be the number of protons, neutrons and electrons in the isotope?

Q. An atom of an element has 26 electrons and has a mass number 56. The nucleus of this atom contains____neutrons.

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What did Rutherford conclude regarding the atomic mass? (i) Mass of the atom is uniformly distributed. (ii) Nucleus of an atom is much heavier than electron. (iii) Nearly all the mass of an atom resides at the centre of an atom. (iv) Nucleus of an atom is lighter than the electron.

What did Rutherford conclude regarding the atomic mass?
(i) Mass of the atom is uniformly distributed.
(ii) Nucleus of an atom is much heavier than electron.
(iii) Nearly all the mass of an atom resides at the centre of an atom.
(iv) Nucleus of an atom is lighter than the electron.