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Chemistry exam questions > Atomic theory 4 > Flashcards

Atomic theory 4 Flashcards

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1
Q

Define radioactivity (L.C)

A

The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.

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2
Q

What change takes place in the structure of the nucleus of an atom when beta decay occurs? (L.C)

A

A neutron changes into a proton.

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3
Q

Write a balanced equation for the beta decay of a carbon-14 nucleus. (L.C)

A

C → N + e (number have to be written in - marking scheme)

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4
Q

A piece of fossilised yew, from a tree that was alive about 6000 years ago, was excavated from Boora Bog, Co. Offaly. When a tiny fragment of it was analysed, it was found to contain 1.5 x 10(₁₂) carbon-14 atoms. (i)Explain why the fragment of yew must have contained 3.0 x 10(₁₂) carbon-14 atoms 5730 years before the analysis. (ii) What mass of carbon-14 did the fragment contain 5730 years before the analysis? (L.C)

A

(i) 5730 is the half-life

(ii) 3.0 × 10₁₂ ÷ 6.0 × 10₂₃ = 5.0 × 10-₁₂ (=originally)
5.0 × 10-₁₂ × 14* = 7.0 × 10-₁₁
(small numbers mean to the power of)

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5
Q

What are isotopes? (L.C)

A

Isotopes are atoms of the same element that have the same atomic number but different mass numbers due to the different numbers of neutrons present in the nucleus.

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6
Q

What is a radioisotope? (L.C)

A

An isotope with unstable nucleus

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7
Q

Define the half-life of a radioisotope. (L.C)

A

This is the time taken for half the nuclei in a given sample to decay.

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8
Q

Complete the following nuclear equation to show the alpha decay of radium-226. Ra ⇾ ___ + ___ (L.C)

A

Rn + He

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9
Q

Radium-223 undergoes alpha decay and is also used in radiotherapy. Starting with a sample containing 1.0 x 10(-4) moles of radium-223, how many of these atoms remain when 87.5% of the sample has decayed? (L.C)

A

1 × 10-₄ × 12.5 ÷ 100 = 1.25 x 10-₅

1.25 x 10-₅ x 6.0 x 10₂₃ = 7.5 x 10₁₈

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10
Q

What change takes place in the nucleus of an atom when beta decay occur? (L.C)

A

A neutron changes into a proton and an electron that is emitted.

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11
Q

Write a balanced nuclear equation for the beta-decay of the Fr nucleus (223 - top, 87 - bottom) (L.C)

A

Fr → Ra + e

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12
Q

Define radioactivity (L.C)

A

The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.

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13
Q

Give two differences between chemical reactions and nuclear reactions. (L.C)

A

chemical: involves electrons and no change to nucleus
nuclear: electron cloud not involved and nuclear change

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14
Q

Give two properties of beta-particles. (L.C)

A
  • Negative
  • Moderately ionising
  • Less penetrating power than α
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15
Q

A certain mass of caesium-137 leaked on a particular day. What fraction of this mass remained as caesium-137 after 90 days? (L.C)

A

One-eighth

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16
Q

What are isotopes? (L.C)

A

Atoms of the same element that have the same atomic number but different mass numbers due to the different numbers of neutrons present in the nucleus.

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17
Q

Define radioactivity. (L.C)

A

The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.

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18
Q

Define radioisotope. (L.C)

A

An isotope with unstable nucleus.

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19
Q

Carbon-14 decays by the beta particle emission. Write a balanced equation to describe beta-decay of the carbon-14 nucleus. (L.C)

A

(14 - top, 6 bottom)C → e + N

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20
Q

Explain why the carbon-12 to carbon-14 isotope ratio in the shoe leather changed over 5500 years since the shoe was made. (L.C)

A

Carbon-14 decayed and changed to nitrogen

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21
Q

Define radioactivity (L.C)

A

The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.

22
Q

Define the half-life of a radioactive isotope. (L.C)

A

The time taken for half of the radioactive isotopes in a sample to decay.

23
Q

Alpha particles are hazardous to human health. State two risk associated with exposure to alpha radiation.

A

Causes mutation and cancer

24
Q

Explain why the occupants of a house fitted with smoke detectors containing americium-241 are not at risk from alpha radiation emitted by these devices. (L.C)

A

Radiation is not very penetrating

25
Q

Householders are advised to replace the batteries in smoke detectors regularly. Explain whether or not the americium-241 needs to be replaced regularly also. (L.C)

A

No as half life is over 400 years and sample does not deplete quickly

26
Q

What change occurs in the nucleus of an atom when it undergoes beta emission. (L.C)

A
  • Neutron changes to proton
27
Q

Give two properties of alpha particles. (L.C)

A
  • Positive charge
  • Poor penetration
  • Stopped by a few sheets of paper
28
Q

Give two differences between a nuclear reaction and a chemical reaction. (L.C)

A
  • Involves nucleus of atoms not electron cloud

- Involves new elements being generated

29
Q

Define radioactivity. (L.C)

A

The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.

30
Q

State three properties of beta particles. (L.C)

A
  • Negative
  • Moderately ionising
  • Less penetrating power than α
31
Q

Explain how the carbon-14 isotope allows certain archaeological discoveries to be dated. (L.C)

A
  • In living things, the ratio of carbon-12 to carbon-14 is constant.
  • Decrease in carbon-14 related to time passed since death.
32
Q

List the following three types of radiation in order of increasing penetrating power. Alpha, beta, gamma (L.C)

A

Alpha, beta, gamma

33
Q

Explain how Rutherford interpreted the results of his experiment to conclude that the atom has a nucleus. (L.C)

A
  • Mass concentrated / atoms mainly made up of empty space.
34
Q

What are alpha particles? (L.C)

A

Two protons and two neutrons

35
Q

Describe an experiment carried out by Rutherford and his co-workers that led to the discovery of the nucleus. (L.C)

A
  • Bombarded gold foil with alpha particles
  • Used zinc sulfide detector
  • Most passed straight through
  • Some were deflected at large angles
  • Some were reflected
36
Q

What change occurs in the nucleus of an atom when beta decay occurs?

A

A neutron changes into a proton.

37
Q

Bananas contain small quantities of potassium-40, a radioactive isotope. What is the daughter nucleus when K-40 emits an electron in beta decay?

A

Calcium-40

38
Q

What is an isotope.

A

Atoms of the same element that have the same atomic number but different mass numbers due to the different numbers of neutrons present in the nucleus.

39
Q

The carbon-14 isotope is a beta particle emitter. What is a beta particle?

A

An electron emitted from the nucleus.

40
Q

List two properties of beta particles.

A
  • Negative charge
  • High-speed
  • Negligible mass
41
Q

Define radioactivity.

A

The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.

42
Q

What are isotopes

A

Atoms of the same element that have the same atomic number but different mass numbers due to the different numbers of neutrons present in the nucleus.

43
Q

Define relative atomic mass, Ar.

A

The average mass of an atom of an elements compared to 1/12 the mass of the carbon - 12 isotope, taking relative abundances of the naturally occuring isotopes into account.

44
Q

Calculate the relative atomic mass of a sample of silicon, given that a mass spectrometer shows that it consists of 92.2% of ₂₈Si, 4.7% of ₂₉Si and 3.1% of ₃₀Si.

A

Answer - 28.109

45
Q

Name the scientist who is credited with having discovered radioactivity.

A

Bacquerel

46
Q

Define radioactivity.

A

The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.

47
Q

What is an alpha particle and state two of its properties.

A

A positive particle consisting of two protons and two neutrons.

  • Positively charged
  • Poor penetration
48
Q

Complete the equation for the nuclear reaction involved in the alpha decay of americium-241 (Am) to
neptunium (Np)
(95)Am → _Np + ____ + energy

A

(237) (93)Np + He

49
Q

What are isotopes?

A

Atoms of the same element that have the same atomic number but different mass numbers due to the different numbers of neutrons present in the nucleus.

50
Q

What is a radioisotope?

A

An isotope with unstable nucleus.

51
Q

Define the half-life of a radioisotope.

A

The time taken for half of the radioactive isotopes in a sample to decay.

52
Q

Calculate the relative atomic mas of a sample of neon, given that a mass spectrometer shows that it consists of 90.9% of 20Ne, 0.3% of 21Ne and 8.8% of 22Ne.

A

Answer - 20.179

Chemistry exam questions (29 decks)

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