Fig. 1 shows the arrangement used in an early particle-scattering investigation. A radioactive source inside a lead cap sends alpha particles towards a very...
Question 1 Report
Fig. 1 shows the arrangement used in an early particle-scattering investigation. A radioactive source inside a lead cap sends alpha particles towards a very thin metal foil. A circular detector records flashes of light when particles strike it. Most particles passed straight through, a few changed direction, and very few returned towards the source. The result changed the model of the atom used by scientists.
(a) What type of radiation was directed at the foil? [1]
(b) Which observation shows that an atom is mostly empty space? [1]
(c) Describe what the few particles that returned towards the source showed about the nucleus. [2]
(d) Give one reason why a lead cap was used around the source. [1]
Fig. 1 shows two atoms collected from carbon dioxide in a greenhouse experiment. Both atoms are carbon because they have the same proton number. One atom is carbon-12 and the other is carbon-14. Carbon-14 is radioactive and can release radiation, whereas carbon-12 is stable. The diagram helps students compare isotopes without suggesting that neutrons carry electrical charge.
(a) What is meant by the term isotope? [2]
(b) Which particle number is the same in both atoms in Fig. 1? [1]
(c) Calculate the mass number of the carbon-14 atom. [1]
(d) Give one reason why carbon-12 and carbon-14 have similar chemical properties. [1]
Answer Details
First set of questions: alpha scattering
(a) The foil was directed with alpha radiation, or alpha particles. [1]
(b) The observation that most particles passed straight through shows that most of the atom is empty space. [1]
(c) The few particles that returned towards the source showed that the nucleus is very small. Their large deflection also showed that it is positively charged or contains most of the atom's mass. [2]
(d) The lead cap absorbs radiation in directions other than the opening, producing a narrow beam of alpha particles. [1]
Second set of questions: carbon isotopes
(a) Isotopes are atoms of the same element with different numbers of neutrons. They have the same proton number. [2]
(b) The particle number that is the same is the proton number, or number of protons. [1]
(c) Mass number is protons plus neutrons:
\[6+8=14\]
The carbon-14 atom has mass number 14. [1]
(d) Carbon-12 and carbon-14 have similar chemical properties because they have the same number and arrangement of electrons. [1]
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