Revision Library

revisionlibrary.co.uk

GCSE · Chemistry

C1a Atomic Structure and the History of the Atom

AQA 8464 · Calculator allowed · about 77 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

The Changing Model of the Atom

Original text written for Revision Library.

For much of the nineteenth century, scientists pictured the atom as a tiny, solid sphere that could not be divided, created or destroyed, an idea first proposed by John Dalton in the early 1800s. This changed in 1897, when J. J. Thomson's experiments with cathode rays revealed the existence of tiny, negatively charged particles far smaller than a whole atom. Since atoms are electrically neutral overall, Thomson proposed the 'plum pudding model': a sphere of positive charge with negative electrons embedded throughout it, rather like fruit in a pudding. In the early 1900s, Ernest Rutherford directed an experiment in which Hans Geiger and Ernest Marsden fired alpha particles at a thin sheet of gold foil. Most particles passed straight through, but a small number bounced back through large angles. This was not what the plum pudding model predicted, and it led Rutherford to propose a new nuclear model: a tiny, dense, positively charged nucleus surrounded by mostly empty space. Niels Bohr then refined this model further, suggesting that electrons occupy fixed shells at set distances from the nucleus, corresponding to different energy levels. His calculations matched experimental observations closely. Finally, in 1932, James Chadwick provided evidence for the neutron, a particle with no charge found alongside protons in the nucleus, completing the model of the atom used today.

This question is about the particles that make up an atom.

(a)Which subatomic particle has a relative charge of 0 (no charge)?(1)

A) Proton
B) Neutron
C) Electron
D) Nucleus

(b)Name the central region of an atom that contains the protons and neutrons.(1)

(c)Name the particles that move around outside the nucleus.(1)

(Total for Question 1 is 3 marks)

Atoms are made up of three types of subatomic particle: protons, neutrons and electrons.

(a)Complete the table below to show the relative charge of the proton, the neutron and the electron.(3)

(b)Complete the table below to show the relative mass of the proton, the neutron and the electron.(3)

(Total for Question 2 is 6 marks)

'Atomic number' and 'mass number' are used to describe atoms.

(a)Define the term 'atomic number'.(1)

(b)Define the term 'mass number'.(1)

(c)An atom of fluorine has an atomic number of 9 and a mass number of 19. State the number of protons, neutrons and electrons in this atom.(3)

(Total for Question 3 is 5 marks)

The table shows three isotopes of carbon, all with atomic number 6: carbon-12, carbon-13 and carbon-14 (mass numbers 12, 13 and 14 respectively).

(a)Calculate the number of neutrons in an atom of carbon-12.(1)

(b)Calculate the number of neutrons in an atom of carbon-13.(1)

(c)Calculate the number of neutrons in an atom of carbon-14.(1)

(Total for Question 4 is 3 marks)

Two atoms, X and Y, are isotopes of the same element.

(a)Define the term 'isotope'.(2)

(b)Explain why isotopes of the same element have the same chemical properties but can have different physical properties, such as mass.(2)

(Total for Question 5 is 4 marks)

Electrons are arranged in shells around the nucleus of an atom.

(a)State the maximum number of electrons that can occupy each of the first three electron shells, starting with the shell closest to the nucleus.(3)

(b)An atom of silicon has 14 electrons. Write the electronic structure of this atom.(2)

(Total for Question 6 is 5 marks)

The electronic structure of an atom is 2, 8, 7.

(a)State the total number of electrons in this atom.(1)

(b)State the number of electrons in the outer shell of this atom.(1)

(c)Use the periodic table to name this element.(1)

(Total for Question 7 is 3 marks)

In the early 1800s, John Dalton proposed one of the first scientific models of the atom.

(a)Describe Dalton's model of the atom.(2)

(Total for Question 8 is 2 marks)

In 1897, J. J. Thomson discovered that atoms contain smaller, negatively charged particles called electrons.

(a)Describe the 'plum pudding model' of the atom that Thomson proposed.(2)

(b)State why the discovery of the electron meant that Dalton's model of the atom could no longer be correct.(1)

(Total for Question 9 is 3 marks)

In the α particle scattering experiment, a beam of α particles (which are positively charged) was directed at a thin sheet of gold foil.

(a)Most of the α particles passed straight through the gold foil with little or no deflection. Explain what this observation suggests about the structure of the atom.(2)

(b)A small number of α particles were deflected through more than 90 degrees, with a very small number bouncing almost straight back. Explain what this observation suggests about the structure of the atom.(2)

(c)Explain why these results led scientists to reject the plum pudding model in favour of a new nuclear model.(2)

(Total for Question 10 is 6 marks)

Niels Bohr and James Chadwick both contributed to the development of the model of the atom in the early twentieth century.

(a)State how Bohr's model of the atom differed from Rutherford's nuclear model.(2)

(b)State who discovered the neutron, and in which year.(2)

(Total for Question 11 is 4 marks)

The list below shows four scientists whose work contributed to the model of the atom, but not in the correct order: Bohr, Rutherford, Dalton, Thomson.

(a)Put these four scientists in the correct chronological order, from the earliest contribution to the most recent.(2)

(Total for Question 12 is 2 marks)

Use the information in the source text above, and your own knowledge, to answer this question.

Describe how the scientific model of the atom changed over time, from Dalton's model to Bohr's model. In your answer, refer to the experimental evidence that caused scientists to change their ideas at each stage.

(Total for Question 13 is 6 marks)

Priya carried out a flame test as part of the required practical 'Identification of ions by chemical and flame tests', to help identify the metal ion in an unknown compound.

(a)State two safety precautions Priya should take when carrying out this practical.(2)

(b)Priya cleaned the nichrome wire loop with dilute hydrochloric acid before dipping it into each new compound. Explain why this step is necessary.(2)

(c)Explain, in terms of electronic structure, why heating a metal compound in a flame produces light of a characteristic colour.(5)

(d)Priya observed a lilac flame, but her teacher pointed out that a lilac colour can be difficult to see if it is masked by a strong yellow-orange colour caused by sodium contamination. Suggest one improvement to the method that would make the lilac colour easier to observe.(2)

(e)Suggest why it is good practice to repeat each flame test at least twice, using a fresh sample of the compound each time.(2)

(Total for Question 14 is 13 marks)

A sample of chlorine gas contains two isotopes: chlorine-35, with a relative abundance of 75%, and chlorine-37, with a relative abundance of 25%.

(a)Calculate the relative atomic mass of this sample of chlorine. Give your answer to 3 significant figures. Show your working.(3)

(Total for Question 15 is 3 marks)

A sample of magnesium contains three isotopes: magnesium-24 (79% abundance), magnesium-25 (10% abundance) and magnesium-26 (11% abundance).

(a)Calculate the relative atomic mass of this sample of magnesium. Give your answer to 1 decimal place. Show your working.(3)

(Total for Question 16 is 3 marks)

The radius of a typical atom is approximately 1 x 10^-10 m. The radius of the nucleus of the same atom is approximately 1 x 10^-14 m.

(a)Calculate how many times greater the radius of the atom is than the radius of its nucleus.(2)

(Total for Question 17 is 2 marks)

Daniel used a mass spectrometer to analyse a sample of a pure element with atomic number 10. The results are shown below: isotope with mass number 20 has a relative abundance of 90%; isotope with mass number 22 has a relative abundance of 10%.

(a)Calculate the number of neutrons in the isotope with mass number 22.(1)

(b)Calculate the relative atomic mass of this sample of the element. Give your answer to 3 significant figures.(3)

(c)Use the atomic number given to name this element.(1)

(Total for Question 18 is 5 marks)

Higher tier only. Boron has a relative atomic mass of 10.8 and occurs naturally as two isotopes, boron-10 and boron-11.

(a)Calculate the percentage abundance of each isotope. Show your working clearly.(4)

(Total for Question 19 is 4 marks)

Mark scheme · C1a Atomic Structure and the History of the Atom

Question 1

(a) B1 B (neutron)
(a) Answer: B (neutron)
(b) B1 nucleus
(b) Answer: Nucleus
(c) B1 electrons
(c) Answer: Electrons

Question 2

(a) B1 proton: +1 (positive) cao
(a) B1 neutron: 0 (no charge) cao
(a) B1 electron: -1 (negative) cao
(a) Answer: Proton +1, neutron 0, electron -1
(b) B1 proton: 1 cao
(b) B1 neutron: 1 cao
(b) B1 electron: very small / negligible (accept approximately 1/2000 of a proton) oe
(b) Answer: Proton 1, neutron 1, electron very small (negligible)

Question 3

(a) B1 the number of protons in the nucleus of an atom oe
(a) Answer: The number of protons in an atom's nucleus
(b) B1 the total number of protons and neutrons in the nucleus of an atom oe
(b) Answer: The total number of protons and neutrons in an atom's nucleus
(c) B1 protons = 9 cao
(c) B1 neutrons = 10 cao (19 - 9)
(c) B1 electrons = 9 cao
(c) Answer: Protons = 9, neutrons = 10, electrons = 9

Question 4

(a) B1 6 cao
(a) Answer: 6
(b) B1 7 cao
(b) Answer: 7
(c) B1 8 cao
(c) Answer: 8

Question 5

(a) B1 atoms of the same element with the same number of protons (same atomic number) oe
(a) B1 but a different number of neutrons (different mass number) oe
(a) Answer: Atoms of the same element with the same number of protons but a different number of neutrons
(b) B1 chemical properties are the same because isotopes have the same number of electrons (the same electronic structure), so they react in the same way oe
(b) B1 physical properties such as mass differ because isotopes have a different number of neutrons, giving a different mass number oe
(b) Answer: Same chemical properties because they have the same number of electrons/electronic structure; different physical properties (mass) because they have a different number of neutrons

Question 6

(a) B1 1st shell = 2 cao
(a) B1 2nd shell = 8 cao
(a) B1 3rd shell = 8 cao
(a) Answer: 2, 8, 8
(b) B1 first two shells correctly filled, 2, 8 oe
(b) B1 remaining 4 electrons correctly placed in the third shell, giving 2, 8, 4 cao
(b) Answer: 2, 8, 4

Question 7

(a) B1 17 cao
(a) Answer: 17
(b) B1 7 cao
(b) Answer: 7
(c) B1 chlorine cao
(c) Answer: Chlorine

Question 8

(a) B1 atoms are described as solid spheres oe
(a) B1 that cannot be divided, created or destroyed, with a different sphere for each different element oe
(a) Answer: Atoms are solid spheres that cannot be divided; different elements are made of different spheres

Question 9

(a) B1 a sphere (or ball/cloud) of positive charge oe
(a) B1 with negative electrons embedded throughout/within it oe
(a) Answer: A sphere of positive charge with negative electrons embedded within it
(b) B1 Dalton's model described atoms as solid, indivisible spheres, but the discovery of the electron showed that atoms contain smaller particles, so atoms can be divided oe
(b) Answer: Atoms were shown to contain smaller particles (electrons), so could not be solid, indivisible spheres as Dalton described

Question 10

(a) B1 most of the atom is empty space oe
(a) B1 so most α particles were not close enough to any charged region of the atom to be deflected oe
(a) Answer: Most of the atom is empty space
(b) B1 the atom has a small, dense region containing most of its mass (the nucleus) oe
(b) B1 this region has a concentrated positive charge, which strongly repels the positively charged α particles oe
(b) Answer: There is a small, dense, positively charged nucleus at the centre of the atom
(c) B1 the plum pudding model predicted that positive charge (and mass) was spread evenly throughout the atom, so α particles should only ever be deflected by small angles oe
(c) B1 the large deflections actually observed did not match this prediction, so a new model with a small, dense, charged nucleus was needed to explain the results oe
(c) Answer: The plum pudding model could not explain the large deflections observed, so it was replaced by the nuclear model

Question 11

(a) B1 Bohr proposed that electrons orbit the nucleus in fixed shells at set distances (energy levels) oe
(a) B1 his theoretical calculations agreed with experimental observations oe
(a) Answer: Bohr proposed that electrons occupy fixed shells/energy levels at specific distances from the nucleus, supported by calculations that matched experimental results
(b) B1 James Chadwick cao
(b) B1 1932 cao
(b) Answer: James Chadwick, 1932

Question 12

(a) B1 Dalton placed first and Thomson placed second oe
(a) B1 Rutherford placed third and Bohr placed fourth, giving the fully correct order: Dalton, Thomson, Rutherford, Bohr
(a) Answer: Dalton, Thomson, Rutherford, Bohr

Question 13

Level 3 (5-6): A detailed and logically structured description of how the atomic model changed over time, correctly linking each new model to the experimental evidence that caused scientists to accept it. The account is presented in a clear chronological sequence covering Dalton, Thomson, Rutherford and Bohr.
Level 2 (3-4): Accurate description of at least two atomic models, with some correct reference to the experimental evidence linked to a change in model. The account has some logical structure but may lack detail or full chronological order.
Level 1 (1-2): Basic, isolated statements about one or two atomic models, with little or no reference to experimental evidence. The account may not be in chronological order.
Level 0 (0): No relevant content.
Indicative content:
- Dalton described atoms as solid spheres that could not be divided, created or destroyed, with different spheres for different elements.
- Thomson's discovery of the electron (using cathode ray tubes) showed atoms contain smaller, negatively charged particles, leading to the plum pudding model: a sphere of positive charge with electrons embedded in it.
- Rutherford, Geiger and Marsden's alpha particle scattering experiment showed most alpha particles passed straight through gold foil, meaning the atom is mostly empty space, but a small number were deflected through large angles, meaning a small, dense, positively charged nucleus is present.
- These results did not match the predictions of the plum pudding model, so the plum pudding model was replaced by the nuclear model.
- Bohr proposed that electrons orbit the nucleus in fixed shells at specific distances (energy levels); his calculations agreed with experimental observations.
- Chadwick provided evidence for the existence of the neutron in 1932, explaining the difference between atomic number and mass number and refining the nuclear model further.

Question 14

(a) B1 wear eye protection/safety goggles oe
(a) B1 any other sensible precaution, e.g. tie back long hair, use a heatproof mat, do not touch the hot wire loop (any one) oe
(a) Answer: Any two of: wear eye protection, tie back long hair, use a heatproof mat, do not touch the hot wire loop
(b) B1 the acid removes/dissolves any residue of the previous compound from the wire loop oe
(b) B1 this prevents contamination, which could produce a false flame colour for the next sample tested oe
(b) Answer: Cleaning removes any residue from the previous test, preventing contamination that could give a false colour result
(c) B1 electrons in the metal atom/ion absorb energy from the flame oe
(c) B1 electrons move to a higher energy level/shell (become excited) oe
(c) B1 electrons are unstable at the higher level and fall back down to a lower shell oe
(c) B1 energy is released as light of a fixed/specific frequency (colour) as the electron falls back down oe
(c) B1 this frequency/colour differs between elements because the energy gaps between their shells differ, giving each element its own characteristic flame colour oe
(c) Answer: Electrons absorb energy and move to a higher shell; when they fall back down they release energy as light of a specific colour, which differs for each element
(d) B1 view the flame through blue cobalt glass oe
(d) B1 this filters out/absorbs the yellow-orange light from sodium, making the lilac colour easier to see oe
(d) Answer: View the flame through blue cobalt glass to filter out the yellow-orange sodium light
(e) B1 to check that the same colour is seen each time oe
(e) B1 this improves the reliability of the result / reduces the risk of an anomalous result caused by contamination oe
(e) Answer: Repeating the test improves reliability by checking the result is consistent and not due to a contamination anomaly

Question 15

(a) M1 multiplies each isotope mass by its percentage abundance and adds the results, e.g. (35 x 75) + (37 x 25), oe
(a) M1 divides the total by 100 oe
(a) A1 35.5 cao
(a) Answer: 35.5

Question 16

(a) M1 (24 x 79) + (25 x 10) + (26 x 11), oe, = 2432 seen
(a) M1 divides the total by 100 oe
(a) A1 24.3 cao (accept 24.32 correctly rounded to 24.3)
(a) Answer: 24.3

Question 17

(a) M1 divides 1 x 10^-10 by 1 x 10^-14 oe
(a) A1 10 000 (accept 1 x 10⁴) cao
(a) Answer: 10,000 times greater (1 x 10⁴)

Question 18

(a) B1 12 cao (22 - 10)
(a) Answer: 12
(b) M1 (20 x 90) + (22 x 10), oe, = 2020 seen
(b) M1 divides the total by 100 oe
(b) A1 20.2 cao
(b) Answer: 20.2
(c) B1 neon cao
(c) Answer: Neon

Question 19

(a) M1 sets up an equation using x for the percentage of boron-10, e.g. (10x + 11(100 - x)) / 100 = 10.8 oe
(a) M1 correctly expands and rearranges, e.g. 10x + 1100 - 11x = 1080, leading to -x = -20 oe
(a) A1 boron-10 = 20% (ft from a correctly rearranged equation)
(a) A1 boron-11 = 80% cao (100 minus their boron-10 value)
(a) Answer: Boron-10 = 20%, boron-11 = 80%

Atomic Structure and the History of the Atom - Worksheets, Questions and Revision