AQA GCSE Physics. 61 minutes. 61 marks. Q1 to Q5 to be worked through with tutor. Q6 to Q9 to be worked through independently.

Transcription

1 AQA GCSE Physics Atomic Structure 4.4.: Atomic Structure Name: Class: Date: Time: 6 minutes Marks: 6 marks Comments: Q to Q5 to be worked through with tutor. Q6 to Q9 to be worked through independently. Answers: aqa/4.4..pdf Page of 23

2 The diagram shows an atom. How many protons are there in the nucleus of the atom? What is the mass number of the atom? (Total 2 marks) 2 Use the Data Sheet to help you answer this question. This question is about elements and atoms. About how many different elements are found on Earth? Draw a ring around the correct number () The following are parts of an atom: electron neutron nucleus proton Choose from the list the one which: (i) (iii) has no electrical charge; contains two of the other particles; has very little (negligible) mass. (3) (c) Scientists have been able to make new elements in nuclear reactors. One of these new elements is fermium. An atom of fermium is represented by the symbol below. 257 Fm 00 (i) How many protons does this atom contain? How many neutrons does this atom contain? (2) (Total 6 marks) Page 2 of 23

3 3 The diagrams below represent three atoms, A, B and C. Two of the atoms are from the same element. (i) Which of A, B and C is an atom of a different element? Give one reason for your answer. (2) Two of these atoms are isotopes of the same element. (i) Which two are isotopes of the same element? and Explain your answer. (3) (Total 5 marks) Page 3 of 23

4 4 Over 00 years ago, scientists thought the atom was like a plum pudding. The diagram below shows the plum pudding model of the atom. The scientists knew that an atom has negatively charged particles. They also knew that an atom has no overall charge. What did the scientists conclude about the charge on the pudding part of the atom? () Page 4 of 23

5 Two scientists named Rutherford and Marsden devised an experiment to investigate the plum pudding model of the atom. The experiment involved firing alpha particles at a thin sheet of gold. The scientists measured how many of the alpha particles were scattered. Using the plum pudding model, the scientists predicted that only a few of the alpha particles would be scattered by more than 4. Over several months, more than measurements were made. (i) The results from this experiment caused the plum pudding model to be replaced by a new model of the atom. Explain why. (2) Suggest one reason why other scientists thought this experiment provided valid evidence for a new model of the atom. () Page 5 of 23

6 (c) In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate. Describe the model now used for the structure of an atom. In your answer you should: give details of the individual particles that make up an atom include the relative masses and relative charges of these particles. Do not include a diagram in your answer. (6) (Total 0 marks) 5 The diagram below shows the paths of two alpha particles A and B into and out of a thin piece of metal foil. Page 6 of 23

7 The paths of the alpha particles depend on the forces on them in the metal. Describe the model of the atom which is used to explain the paths of alpha particles aimed at thin sheets of metal foil. (3) Scientists used to believe that atoms were made up of negative charges embedded in a positive dough. This is called the plum pudding model of the atom. The diagram below shows a model of such an atom. (i) Explain how the plum pudding model of the atom can explain why alpha particle A is deflected through a very small angle. (2) Page 7 of 23

8 Explain why the plum pudding model of the atom can not explain the large deflection of alpha particle B. (3) (c) We now believe that atoms are made up of three types of particles called protons, neutrons and electrons. Complete the table below to show the relative mass and charge of a neutron and an electron. The relative mass and charge of a proton have already been done for you. PARTICLE RELATIVE MASS RELATIVE CHARGE proton + neutron electron (2) (d) The diagrams below show the nuclei of four different atoms A, B, C and D. (i) State the mass number of C. Page 8 of 23

9 Which two are isotopes of the same element? and Explain your answer. (4) (Total 4 marks) 6 The diagram represents an atom of lithium. (i) Complete the diagram by writing in the spaces the name of each type of particle. Use only words given in the box. Each word may be used once or not at all. electron neutron nucleus proton (3) Which type of particle found inside the atom is uncharged? () (iii) What is the mass number of this atom, 3, 4, 7 or 0? Give a reason for your choice. (2) (Total 6 marks) Page 9 of 23

10 7 The diagram represents an atom of beryllium. Complete the following statements by writing one of the letters, J, K or L, in each box. Each letter should be used only once. The particle with a positive charge is The particle with the smallest mass is The particle with no charge is (2) Give the reason why all atoms have a total charge of zero. () (c) Complete the following sentence. There are several isotopes of beryllium. Atoms of different beryllium isotopes will have different numbers of () Page 0 of 23

11 (d) What happens to the structure of an atom to change it into an ion? () (Total 5 marks) 8 The diagrams represent three atoms X, Y and Z. X Y Z Which two of the atoms are from the same element? Give a reason for your answer. (2) Page of 23

12 In the early part of the 20 th century some scientists investigated the paths taken by positively charged alpha particles into and out of a very thin piece of gold foil. The diagram shows the paths of three alpha particles. Explain the different paths A, B and C of the alpha particles. To gain full marks in this question you should write your ideas in good English. Put them into a sensible order and use the correct scientific words. (3) (Total 5 marks) Page 2 of 23

13 9 In the early part of the 20th century, scientists used the plum pudding model to explain the structure of the atom. Following work by Rutherford and Marsden, a new model of the atom, called the nuclear model, was suggested. Describe the differences between the two models of the atom. (4) Page 3 of 23

14 In their investigation, Rutherford and Marsden fired positively charged alpha particles at a very thin sheet of gold. Over a period of several months, the scientists made over measurements. These measurements showed that: a very small number of alpha particles were deflected backwards from the gold foil. Use the nuclear model to explain this experimental result. (2) (c) Why did the work of Rutherford and Marsden convince many scientists that the plum pudding model of the atom was incorrect? (2) (Total 8 marks) Page 4 of 23

15 Mark schemes 4 9 each for mark [2] 2 90 for one mark (i) neutron for one mark (iii) nucleus for one mark electron for one mark (c) (i) 00 for one mark 57 for one mark [6] 3 (i) B for one mark 2 has a different number of electrons (protons) for one mark (i) A and C for one mark same number of protons / electrons, same nuclear charge different number of neutrons / nuclear masses different for mark each 2 [5] 4 (an equal amount of) positive charge do not accept charge on the atom / nucleus is positive Page 5 of 23

16 (i) a (significant) number of alpha particles were scattered by more than 4 or alpha particles deflected backwards accept (some) measurements / results were unexpected measurements / results could not be explained by plum pudding model or measurements / results did not support predictions can be explained by the nuclear model is insufficient accept measurements / results did not support hypothesis many / (over) measurements / results taken accept Rutherford(and Marsden) were respected scientists or scientists were respected accept measurements / results taken over several months the experiment was repeated many times is insufficient (c) Marks awarded for this answer will be determined by the Quality of Written Communication (QWC) as well as the standard of the scientific response. Examiners should also refer to the information on page 5 and apply a best-fit approach to the marking. 0 marks no relevant content Level ( 2 marks) A brief description is given with some particles correctly named Level 2 (3 4 marks) A description is given with all three particles named plus either the polarity of charge associated with the three particles or the relative mass of the three particles or the relative mass for one particle and the relative charge for one particle given Level 3 (5 6 marks) A more detailed description is given, naming the particles and polarity of charge and either the relative mass is given for at least two particles or the relative charge is given for at least two particles Page 6 of 23

17 Examples of the points made in the response brief description contains protons, neutrons and electrons protons are positive electrons are negative neutrons are uncharged has a nucleus relative charge proton + electron neutron 0 relative mass proton neutron electron (about) / 2000 accept protons and neutrons have the same mass accept electrons have tiny / negligible mass zero mass is neutral more detailed description protons and neutrons make up the nucleus electrons orbit the nucleus electrons are in shells most of the atom is empty space nucleus occupies a very small fraction of the volume of the atom electrons orbit at a relatively large distance from the nucleus most of the mass of the atom is contained in the nucleus the nucleus as a whole is positively charged total number of protons in the nucleus equals the total number of electrons orbiting it in an atom 6 [0] 5 nucleus positive charge / protons in nucleus electrons / negative charges orbit nucleus each for mark 3 (i) positive dough repels positive alpha particles or 2 positive charges repel forces small each for mark 2 large force needed + ves in plum pudding spread out may appear in (i) positive charge must be concentrated / in nucleus (ignore references to electrons) for mark each 3 Page 7 of 23

18 (c), 0 X, l (X = negligible / very small/(/840) (/2000),but not nothing) each row for mark 2 (d) (i) 4 for mark B and C have the same number of protons / atomic number but different number of neutrons / mass number each for mark 3 [4] 6 (i) each correct label scores mark neutron 3 (iii) 7 number of protons and neutrons or number of nucleons or number of particles in the nucleus accept number of particles in the centre only if first answer = 7 [6] 7 L J K all 3 in correct order allow mark for correct 2 Page 8 of 23

19 number of electrons = number of protons accept amount for number (c) neutrons this answer only (d) loses / gains electron(s) [5] 8 Y and Z they have the same number of protons or same atomic number accept they have the same number of electrons or same number of protons and electrons allow only different in number of neutrons N.B. independent marks Quality of written communication for correct use of terms underlined in B or C Q Q A alpha particle passes straight through the empty space of the atom or it is a long way from the nucleus describes 3 tracks correctly for 2 marks describes 2 or track correctly for mark B alpha particle deflected / repelled / repulsed by the (positive) nucleus C alpha particle heading straight for the nucleus is deflected / repelled / repulsed backwards do not accept hits the nucleus do not accept answers referring to refraction do not accept answers in terms of reflected backwards unless qualified in terms of repulsion mention of difference in charge on nucleus negates that track max 2 [5] Page 9 of 23

20 9 any two pairs from: nuclear model mass is concentrated at the centre / nucleus () plum pudding model mass is evenly distributed () accept the nuclear model has a nucleus/the plum pudding model does not have a nucleus for mark nuclear model positive charge occupies only a small part of the atom () plum pudding model positive charge spread throughout the atom () accept electrons in shells/ orbits provided a valid comparison is made with the plum pudding model do not accept on its own do not accept electrons at edge of plum pudding nuclear model electrons orbit some distance from the centre / nucleus () plum pudding electrons embedded in the (mass) of positive (charge) () nuclear model the atom mainly empty space () (c) plum pudding model is a solid mass () to gain credit it must be clear which model is being described do not accept simple descriptions on the diagram without comparison nucleus must be positive to deflect/ repel alpha particles answers in terms of electrons/negative charge causing deflection negates mark answers in terms of reflection negates mark nucleus (very) small so few alpha particles deflected backwards accept most of atom empty space so most pass through many/ measurements taken accept results for measurements accept data valid / reliable 4 findings could not be explained by plum pudding model accept a specific finding that could not be explained eg some alpha particles were deflected backwards [8] Page 20 of 23

21 Examiner reports 3 Most candidates recognised that in B was different from A and C, whilst in A and C were the same element. A number were unable to attempt reasons, a few made responses in terms of crosses, black circles and white circles whilst a pleasing number gained some marks at least for answers in terms of electrons, protons and neutrons. Confusion between protons and neutrons cost some candidates a mark. 4 About one third of the students realised that a positive charge would be needed to make the atom neutral. (i) Unfortunately, this question provided few responses which achieved credit. Many responses simply described, in detail, knowledge of the three principal subatomic particles and our modern model of an atom with the space for alpha particles to pass through, rather than the significance of the unexpected degree of alpha scattering found by Rutherford and Marsden which resulted in the abandoning of the plum pudding model. Less than one fifth of the students scored this mark. Most answers being given in terms of the whole experiment being repeated rather than the compilation of the vast number of individual readings. (c) Most of the students were able to score some marks, although one fifth of the students scored zero and a further tenth did not attempt the question. The names of the three particles were usually given and often the polarity was known. Some students extended their answers and often said far too much about the electron arrangement, talking about covalent and ionic bonding. The basic idea of a nucleus and orbiting electrons was well known but few gave extra detail about size of the nucleus, balance of protons and neutrons etc. However some excellent answers were seen and the question was clearly accessible to most students. The meanings of the terms relative charge and relative mass were not well known. 6 From the responses proffered by the candidates, there was not a good understanding of the composition and position of the three subatomic particles noted in the specification. In part (iii) the answer 7 appeared less frequently than chance might dictate. Where the correct choice of number was made candidates usually gained the second mark as well, although a significant number believed that the mass number = protons + electrons. Page 2 of 23

22 7 (c) (d) Nearly three quarters of candidates scored both marks and a further fifth of candidates scored one mark. Nearly two fifths of the candidates gained this mark, with amount being an alternative to number. Many of the incorrect answers were of the type electrons cancel out the protons, the negatives cancel out the positives, and neutrons were often mentioned instead of either protons or electrons. Over half of candidates gained this mark. Just under two thirds of candidates gained this mark by mentioning either the losing or gaining of electron(s). Many candidates made reference to the outside shell becoming complete as a result; some went too far and were confused with the sharing of electrons as in covalent bonding. A few candidates made the mistake of electrons are lost so leaving a negative charge and as in part, some candidates talked about neutrons or protons being lost/gained instead of electrons. 8 Foundation Tier The two atoms, which were isotopes, were successfully identified by the majority of candidates, with an appropriate reason stated. Too many candidates simply described the tracks rather than explain why the alpha particle would take each of the paths shown. To score maximum marks, explanations were needed using scientific words to indicate that candidates were applying their scientific knowledge that repulsion will occur between similarly charged particles. Higher Tier The two atoms, which were isotopes, were successfully identified by a majority of candidates with an appropriate reason stated. Too many candidates simply described the tracks rather than explain why the alpha particle would take each of the paths shown. To score maximum marks, explanations were needed using scientific words to indicate that candidates were applying their scientific knowledge that repulsion will occur between similarly charged particles. 9 This question was generally not well answered. The major issue with candidate responses is that few have any idea about writing an answer structured to contrast the differences. The second part of a comparison often appearing in a different part of the text. Some candidates failed to identify which model was which and many candidates merely described the two diagrams. There was a commonly expressed belief that the plum pudding model was a positively charged particle overall and often that it was a large nucleus. The position of the electrons in this structure was frequently thought to be superficial, and in a significant number of cases it was thought that the label on the model meant that the electrons were positive. Answers were often unclear, with evidence that candidates had not always read the information given in the stem of the question. Many candidates wrote about alpha particles passing through rather than about the deflections. Others wrote about electrons being deflected. Many candidates believed that the deflections were due to interaction with electrons. Page 22 of 23

23 (c) Most candidates were unable to link the information provided to the idea of change and the reasons why scientists may decide a scientific model is no longer acceptable. Page 23 of 23