Atomic theory 4 Flashcards
Define radioactivity (L.C)
The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.
What change takes place in the structure of the nucleus of an atom when beta decay occurs? (L.C)
A neutron changes into a proton.
Write a balanced equation for the beta decay of a carbon-14 nucleus. (L.C)
C → N + e (number have to be written in - marking scheme)
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)
(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)
What are isotopes? (L.C)
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.
What is a radioisotope? (L.C)
An isotope with unstable nucleus
Define the half-life of a radioisotope. (L.C)
This is the time taken for half the nuclei in a given sample to decay.
Complete the following nuclear equation to show the alpha decay of radium-226. Ra ⇾ ___ + ___ (L.C)
Rn + He
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)
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
What change takes place in the nucleus of an atom when beta decay occur? (L.C)
A neutron changes into a proton and an electron that is emitted.
Write a balanced nuclear equation for the beta-decay of the Fr nucleus (223 - top, 87 - bottom) (L.C)
Fr → Ra + e
Define radioactivity (L.C)
The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.
Give two differences between chemical reactions and nuclear reactions. (L.C)
chemical: involves electrons and no change to nucleus
nuclear: electron cloud not involved and nuclear change
Give two properties of beta-particles. (L.C)
- Negative
- Moderately ionising
- Less penetrating power than α
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)
One-eighth
What are isotopes? (L.C)
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.
Define radioactivity. (L.C)
The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.
Define radioisotope. (L.C)
An isotope with unstable nucleus.
Carbon-14 decays by the beta particle emission. Write a balanced equation to describe beta-decay of the carbon-14 nucleus. (L.C)
(14 - top, 6 bottom)C → e + N
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)
Carbon-14 decayed and changed to nitrogen
Define radioactivity (L.C)
The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.
Define the half-life of a radioactive isotope. (L.C)
The time taken for half of the radioactive isotopes in a sample to decay.
Alpha particles are hazardous to human health. State two risk associated with exposure to alpha radiation.
Causes mutation and cancer
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)
Radiation is not very penetrating
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)
No as half life is over 400 years and sample does not deplete quickly
What change occurs in the nucleus of an atom when it undergoes beta emission. (L.C)
- Neutron changes to proton
Give two properties of alpha particles. (L.C)
- Positive charge
- Poor penetration
- Stopped by a few sheets of paper
Give two differences between a nuclear reaction and a chemical reaction. (L.C)
- Involves nucleus of atoms not electron cloud
- Involves new elements being generated
Define radioactivity. (L.C)
The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.
State three properties of beta particles. (L.C)
- Negative
- Moderately ionising
- Less penetrating power than α
Explain how the carbon-14 isotope allows certain archaeological discoveries to be dated. (L.C)
- In living things, the ratio of carbon-12 to carbon-14 is constant.
- Decrease in carbon-14 related to time passed since death.
List the following three types of radiation in order of increasing penetrating power. Alpha, beta, gamma (L.C)
Alpha, beta, gamma
Explain how Rutherford interpreted the results of his experiment to conclude that the atom has a nucleus. (L.C)
- Mass concentrated / atoms mainly made up of empty space.
What are alpha particles? (L.C)
Two protons and two neutrons
Describe an experiment carried out by Rutherford and his co-workers that led to the discovery of the nucleus. (L.C)
- Bombarded gold foil with alpha particles
- Used zinc sulfide detector
- Most passed straight through
- Some were deflected at large angles
- Some were reflected
What change occurs in the nucleus of an atom when beta decay occurs?
A neutron changes into a proton.
Bananas contain small quantities of potassium-40, a radioactive isotope. What is the daughter nucleus when K-40 emits an electron in beta decay?
Calcium-40
What is an isotope.
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.
The carbon-14 isotope is a beta particle emitter. What is a beta particle?
An electron emitted from the nucleus.
List two properties of beta particles.
- Negative charge
- High-speed
- Negligible mass
Define radioactivity.
The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.
What are isotopes
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.
Define relative atomic mass, Ar.
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.
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.
Answer - 28.109
Name the scientist who is credited with having discovered radioactivity.
Bacquerel
Define radioactivity.
The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.
What is an alpha particle and state two of its properties.
A positive particle consisting of two protons and two neutrons.
- Positively charged
- Poor penetration
Complete the equation for the nuclear reaction involved in the alpha decay of americium-241 (Am) to
neptunium (Np)
(95)Am → _Np + ____ + energy
(237) (93)Np + He
What are isotopes?
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.
What is a radioisotope?
An isotope with unstable nucleus.
Define the half-life of a radioisotope.
The time taken for half of the radioactive isotopes in a sample to decay.
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.
Answer - 20.179
