4.1 The structure of the atom and isotopes
8 exam questions worth 19 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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Which two particles are found in the nucleus of an atom?
Choose one answer.
Correct Not quite: the answer is Protons and neutrons
Mark scheme
B: Protons and neutrons
Model answer
Protons and neutrons (B). The electrons are outside the nucleus.
What is the approximate radius of an atom?
Choose one answer.
Correct Not quite: the answer is 1 × 10⁻¹⁰ m
Mark scheme
B: 1 × 10⁻¹⁰ m
Model answer
1 × 10⁻¹⁰ m (B). The nucleus is much smaller, around 1 × 10⁻¹⁵ m.
Chlorine has the nuclear notation ^{35}_{17}\text{Cl}. State the number of protons, neutrons and electrons in a neutral atom of chlorine-35.
Mark scheme
protons = 17 (1); neutrons = 35 − 17 = 18 (1); electrons = 17 (1)
Model answer
Protons = atomic number = 17. Neutrons = mass number − atomic number = 35 − 17 = 18. A neutral atom has the same number of electrons as protons, so 17 electrons.
Explain why an atom has no overall electrical charge.
Mark scheme
the number of protons equals the number of electrons (1); protons are +1 and electrons are −1, so the charges cancel out (1)
Model answer
An atom has the same number of protons and electrons. Each proton has a charge of +1 and each electron −1, so the charges cancel.
Describe two ways in which an atom of carbon-12 and an atom of carbon-14 are the same and one way they are different.
Mark scheme
same number of protons (6) (1); same number of electrons (1); different number of neutrons (6 and 8) / different mass number (1)
Model answer
Both have 6 protons and 6 electrons. They differ in the number of neutrons: carbon-12 has 6 and carbon-14 has 8.
A magnesium atom has atomic number 12. It loses two electrons to form an ion. State the number of protons and electrons in the ion, and its charge.
Mark scheme
protons = 12 (1); electrons = 10 (1); charge = +2 (1)
Model answer
Protons = 12 (this never changes). Electrons = 12 − 2 = 10. There are two more protons than electrons, so the ion has a charge of +2.
Lithium-6 and lithium-7 are isotopes of lithium. They have the same chemical properties but different masses. Explain why.
Mark scheme
same number of protons and electrons (1); chemical properties depend on the electrons (1); different numbers of neutrons, so different mass (1)
Model answer
The isotopes have the same number of electrons, and chemical properties depend on the electrons. They have different numbers of neutrons, so their masses are different.
An electron in an atom absorbs electromagnetic radiation. Describe what happens to the electron, and what happens when it later returns to its original energy level.
Mark scheme
the electron moves to a higher energy level / further from the nucleus (1); when it falls back to the lower level (1); it emits electromagnetic radiation (1)
Model answer
The electron moves up to a higher energy level, further from the nucleus. When it falls back down to its original level, it emits electromagnetic radiation.
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