Journey Inside the Atom

In Rutherford's α-particle scattering experiment, the observation that MOST α-particles passed through the gold foil undeflected led to the conclusion that:

1. aThe atom has a positively charged nucleus
2. bMost of the atom is empty space
3. cElectrons revolve in fixed orbits
4. dα-particles repel each other

Which of the following BEST explains why a few α-particles bounced back during Rutherford's experiment?

1. aElectrons in the gold foil repelled them
2. bα-particles collided with each other
3. cGold has high density everywhere
4. dA small, dense, positively-charged nucleus deflected them by Coulomb repulsion

An atom has atomic number 17 and mass number 37. The numbers of electrons, protons and neutrons respectively are:

1. a17, 17, 37
2. b17, 20, 17
3. c20, 17, 17
4. d17, 17, 20

The electronic configuration of an atom with \(Z = 20\) is:

1. a2, 8, 10
2. b2, 8, 8, 2
3. c2, 10, 8
4. d2, 8, 8, 8

Atom X has the electronic configuration 2, 8, 3 and atom Y has 2, 6. One atom of X can combine with how many chlorine atoms, and one atom of Y with how many hydrogen atoms?

1. a5 and 6
2. b3 and 6
3. c3 and 2
4. d5 and 2

Deuterium and tritium are isotopes of hydrogen. Compared with a deuterium atom, a tritium atom has:

1. aone more proton and one more electron
2. bone more neutron and the same number of electrons
3. cone more neutron and one more electron
4. done more electron and the same number of neutrons

Isotopes of an element have:

1. aSame mass number, different atomic number
2. bDifferent atomic number, different mass number
3. cSame mass number, same atomic number
4. dSame atomic number, different mass number

The average atomic mass of chlorine is 35.5 u. Natural chlorine is a mixture of Cl-35 and Cl-37. The percentage of Cl-35 in nature is approximately:

1. a50%
2. b25%
3. c75%
4. d65%

The maximum number of electrons in the L-shell, M-shell and N-shell respectively (by \(2n^{2}\) rule) are:

1. a8, 18, 32
2. b2, 8, 18
3. c8, 8, 18
4. d8, 18, 8

Which of the following statements about Thomson's atomic model is correct?

1. aIt correctly described the nucleus as small and dense
2. bIt described the atom as a uniform sphere of positive charge with electrons embedded like seeds in a watermelon
3. cIt explained the existence of fixed orbits for electrons
4. dIt explained the line spectra of hydrogen

Assertion (A): Rutherford's model of the atom could not explain why atoms are stable.

Reason (R): An electron revolving around the nucleus is accelerating, so it should keep losing energy and spiral into the nucleus.

1. aBoth A and R are true, and R is the correct explanation for A
2. bBoth A and R are true, but R is NOT the correct explanation for A
3. cA is true, but R is false
4. dA is false, but R is true

Assertion (A): Isotopes of an element show identical chemical behaviour.

Reason (R): Chemical properties depend on the number of valence electrons, which is the same for isotopes.

1. aBoth A and R are true, and R is the correct explanation for A
2. bBoth A and R are true, but R is NOT the correct explanation for A
3. cA is true, but R is false
4. dA is false, but R is true

Assertion (A): Most of the mass of an atom is concentrated in its nucleus.

Reason (R): Electrons are much heavier than protons.

1. aBoth A and R are true, and R is the correct explanation for A
2. bBoth A and R are true, but R is NOT the correct explanation for A
3. cA is true, but R is false
4. dA is false, but R is true

Assertion (A): The valency of magnesium (2,8,2) is 2.

Reason (R): Magnesium loses its two outermost electrons to achieve the stable octet of neon.

1. aBoth A and R are true, and R is the correct explanation for A
2. bBoth A and R are true, but R is NOT the correct explanation for A
3. cA is true, but R is false
4. dA is false, but R is true

1. I. Electrons revolve only in fixed orbits with definite energies.
2. II. An electron in a Bohr orbit continuously emits electromagnetic radiation.
3. III. Energy is emitted or absorbed only when an electron jumps between orbits.

Which of the above statements about Bohr's model is/are correct?

1. aI and II only
2. bII and III only
3. cI, II and III
4. dI and III only

1. I. Calcium (atomic number 20) and argon (atomic number 18), each with mass number 40, are isobars.
2. II. Isobars are atoms of different elements with the same total number of nucleons.
3. III. Isobars have the same chemical properties because they have the same mass number.

Which of the statements above about isobars is/are correct?

1. aOnly I
2. bOnly II and III
3. cOnly I and II
4. dI, II and III

1. I. Isotopes of an element have the same atomic number but different mass numbers.
2. II. Isotopes of an element have the same mass.
3. III. Isotopes show the same chemical properties.

Which statement(s) about isotopes is/are correct?

1. aI and II
2. bII and III
3. cI, II and III
4. dI and III

1. I. Valency is the number of electrons gained, lost or shared by an atom to complete its octet.
2. II. Atoms with a complete octet in the outermost shell (or 2 electrons in the case of helium) are largely unreactive.
3. III. Chlorine (2, 8, 7) gains one electron to complete its octet, so its valency is 1.

Which of the above statements about valency is/are correct?

1. aI only
2. bI, II and III
3. cI and II
4. dII and III

Match List I with List II:

1. a(i)-S, (ii)-Q, (iii)-R, (iv)-P
2. b(i)-S, (ii)-Q, (iii)-P, (iv)-R
3. c(i)-Q, (ii)-S, (iii)-P, (iv)-R
4. d(i)-Q, (ii)-S, (iii)-R, (iv)-P

Match each isotope in List I with its use in List II:

1. a(i)-P, (ii)-Q, (iii)-S, (iv)-R
2. b(i)-Q, (ii)-S, (iii)-P, (iv)-R
3. c(i)-Q, (ii)-P, (iii)-S, (iv)-R
4. d(i)-R, (ii)-P, (iii)-S, (iv)-Q

Match each atom in List I with the number of neutrons in its nucleus in List II:

1. a(i)-R, (ii)-P, (iii)-S, (iv)-Q
2. b(i)-R, (ii)-S, (iii)-P, (iv)-Q
3. c(i)-P, (ii)-S, (iii)-R, (iv)-Q
4. d(i)-R, (ii)-S, (iii)-Q, (iv)-P

For a science fair, Kabir makes a bead model of a sulfur atom (atomic number 16, mass number 32). He puts red beads for protons and white beads for neutrons in the centre, and blue beads for electrons on rings for the shells, starting from the innermost ring. Which model is correct?

1. a16 red and 32 white beads; blue beads on rings of 2, 8, 6
2. b16 red and 16 white beads; blue beads on rings of 2, 6, 8
3. c16 red and 16 white beads; blue beads on rings of 2, 8, 6
4. d16 red and 16 white beads; blue beads on rings of 2, 14

Why is the M-shell of potassium (\(Z = 19\), configuration 2,8,8,1) NOT filled to its full capacity of 18 before the N-shell starts filling?

1. aOnce the outermost shell has 8 electrons, additional electrons go to the next shell first to maintain stability (octet)
2. bThe \(2n^{2}\) rule does not apply to potassium
3. cM-shell capacity is actually 8, not 18
4. dElectrons cannot enter the M-shell after the L-shell is full

In a class game, each student holds a card for one atom. Aman's card shows an atom with \(Z = 11\). When this atom loses one electron to complete its octet, its electron distribution becomes the same as that of which atom?

1. aHelium (\(Z = 2\))
2. bArgon (\(Z = 18\))
3. cMagnesium (\(Z = 12\))
4. dNeon (\(Z = 10\))

According to the timeline, whose idea of the atom was the first to be based on scientific experiments rather than imagination?

1. aAcharya Kanada
2. bJohn Dalton
3. cDemocritus
4. dJ. J. Thomson

From his study of cathode rays (in the timeline), Thomson concluded that electrons are present in all atoms. Which observation supported this?

1. aThe rays moved from the anode to the cathode
2. bThe rays were streams of positively charged particles
3. cThe nature of the rays did not depend on the cathode material or the gas in the tube
4. dThe rays passed straight through a thin gold foil

The timeline ends with electrons pictured as 'electron clouds'. In this modern picture:

1. awe can predict the regions where electrons are most likely to be, not exactly where they are
2. belectrons are spread through a sphere of positive charge
3. celectrons sit inside the nucleus with the protons and neutrons
4. delectrons move in fixed circular orbits, exactly as Bohr proposed

Of the discoveries in the timeline, which was the first to show that the atom is not indivisible, as Kanada and Dalton had believed?

1. aThe gold foil experiment of 1911
2. bChadwick's discovery of the neutron in 1932
3. cBohr's shells of 1913
4. dThomson's study of cathode rays in 1897

Which element is paired with its correct symbol and the correct reason for that symbol?

1. aSodium, Na — from its English name
2. bCobalt, CO — the first two letters of its name
3. cIron, Fe — from its Latin name ferrum
4. dPotassium, Po — the first two letters of its name

The diameter of an atom is about \(10^{-10}\) m and that of its nucleus about \(10^{-15}\) m. If an atom were enlarged to the size of a cricket ground 100 m across, about how wide would its nucleus be?

1. a1 cm
2. b1 mm
3. c1 m
4. d0.01 mm