Chemistry

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Chemistry

  1. 1. SCIENCE Teacher Instruction Manual Chemistry & Physics Copyright © 2007 National Institute of Education - Sri Lanka. All rights reserved. Grade 10 2007 Department of Science, Health & Physical Education Faculty of Science &Technology National Institute of Education
  2. 2. Science Grade 10 Chemistry & Physics 2007 Copyright © 2007 National Institute of Education - Sri Lanka. All rights reserved. © National Institute of Education ISBN- Department of Science, Health & Physical Education, Faculty of Science &Technology, National Institute of Education. Printing: NIE Press, National Institute of Education, Maharagama. i
  3. 3. Message of the Director General The first curriculum revision for the new millennium is based on the elimination of the several problems obtaining in the present education system. The present curriculum reforms have been planned having identified the problems that youth face consequent to the weakening of their thinking abilities, social abilities as well as personal abilities and step by step exploration of factors leading to this situation, to overcome which, the necessary background was prepared. Compared to the other countries in the Asian region, our country took the lead in education in earlier years. But most countries in this region have superceded Sri Lanka in education today. Some factors that influenced this deterioration are the action taken by educational institutions to continue to take action to confirm the known, learn that which had been decided on earlier, and reconstruct that which was, in the same form itself. All these matters have been taken into consideration and the officers of the National Institute of Education have endeavoured to prepare the new curriculum on the basis of a distinct philosophy. The primary objective here is to change that which is known, explore that which is new and develop that which is necessary for tomorrow and build up a generation of students who can display their readiness for a successful future. But there is no need to reiterate, the need for a visible change in the teacher’s role for the realization of this objective. In place of the obvious transactional teacher role presenting in our classrooms so far, the Sri Lankan school teacher will have to understand and conform to a student-centered, competency based and activity focused transformational role. It is our firm belief that this Teacher Instruction Manual will serve you as an aid to become an effective teacher through the provision of numerous instructions that will help you adapt to the new situation. Through the study of these instructions you will be provided the opportunity of making your daily teaching as well as the evaluation task easy. There is no doubt that instructions for student exploration and other quality inputs will help facilitate the teacher’s task. Similarly, the Teacher Instruction Manual will help convey to school principals valuable information they can use in time-tabling, sharing of limited resources and internal supervision. My sincere thanks go to Dr. Mrs. I. L. Ginige, Assistant Director General (Curriculum Development) Science & Technology Faculty of National Institute of Education for her direct involvement in the preparation of this Teacher Instruction Manual that will serve an immense purpose in the task performed at school level by the section above and also teacher educationist involved in beginning or continuous teacher educational matters, in-service advisors as well as officers at various levels, involved in external supervision plus monitoring programmes. Professor J. W. Wickramasinghe Director General National Institute of Education iii
  4. 4. Preface The first curriculum reform for the millennium implemented with the aim of preparing a powerful basis for a new Sri Lanka anticipates a visible transformation of the teacher’s role. The three main sections below are included in the Teacher Instruction Manual prepared with the objective of providing the teacher with the necessary support in this regard. · Detailed Syllabus · Activity Continuum that helps in the implementation of the syllabus · Instruments for the extension of the learning teaching process. Teachers have been provided the opportunity of understanding several basic matters that have been taken into consideration in the preparation of the curriculum for the detailed syllabus extending beyond subject topics and sub-topics. Competency levels that correspond to subject competency have been included in this section that commences with an introduction to the factors and subject aims that formed the basis of the new syllabus. One special features of this section is that, while the knowledge-base determined under competency level each student needs to develop has been introduced as the subject content the multiple learning and teaching methods employed in transmitting this section to the student has also been taken into consideration in determining the time frame with respect to each competency level. The final part of the detailed syllabus presented under the heading “School Policy and Programs” needs to be studied very carefully and understood by every instructional leader. This section provides school managers a range of valuable instructions to assist them in the allocation for teaching, subject-teaching assigning functions to teachers, implementing co-curricular activities as well as supervision of the teacher’s task. The second section of the Teacher Instruction Manual has been prepared with the objective of providing teachers with clear understanding of the proposed learning- teaching methodology. This section commences with the introduction of the methods of planning activities under competency-based education as well as the change in the teacher’s role. Although the activity continuum necessary for the implementation of the curriculum has been introduced next, the implementation of the proposed activity in the very same manner is not expected of teachers. The teacher should endeavor to make use of his / her creative, as well as critical thinking abilities and adapt these activities in a manner that suits ones class, best. Although instructions have been provided on the constitution of groups in keeping with the facets of the problems subject to exploration, the teacher is expected to take an intelligent decision on the number of groups based on number of students in the class. iv
  5. 5. Time has been allocated for activities to ensure achievement of the relevant competency levels. Therefore, teachers may have to exceed the 40-minute period. While each activity has been provided adequate time for the actualization of each competency level, the teacher is expected to make use of single or double periods in the time table and breakdown these activities, as suitable in implementing them. For the success of the procedure it is essential that every time an activity commenced the previous day is carried over to the following day, that a brief summary of the part of the activity completed the previous day is presented to the class. Similarly, this decision will provide the school community with the opportunity of involving students in effective learning where teachers obtain leave of absence. The final item in this section is a list of quality inputs necessary for the maintenance of the quality of subject learning and teaching, when taken as a whole. As such, the teacher has a choice of ordering out the necessary learning-teaching materials in time and having them on hard. Included in the third part of the teacher Instruction Manual under the title “ Assessment and evaluation” are a number of important hints to ensure that the expected results of the exercise are realized. This section has been so structured as to introduce matters related to the assessment and evaluation that should take place under each activity, extension of the learning and teaching that takes place based on activity groups and the nature of the questions that might be expected in general examinations. It must be pointed out that the primary responsibility of the teachers is to Identify instances where assessment and evaluation can be implemented in the course of each activity and to carry out this task successfully on the basis of common criteria. The set of instruments prepared with a range of activities as the objective for the purpose of extending learning and teaching provide students with the opportunity of involvement in continuous learning outside the recommended classroom sessions. While it is the task of the teacher to regularly examine the learning students receive, based on these instruments, and encourage them, arriving at a correct decision regarding the final results of the activities and communicating that decision to the relevant parties is expected of the teacher. It is essential that a visible change takes place in general examinations for the success of the learning-teaching process. The National Institute of Education, with the assistance of the Sri-Lanka Department of Examinations, has introduced several prototype questions for educational levels that terminate with these examinations. Since this change in examination question papers has been suggested in order to direct students to learn through practice and experience, instead of resorting to mechanical approaches like memorizing or answering model question papers, the education of school students and parents about this change should commence at the beginning itself. v
  6. 6. All teachers should realize that various activities can be developed for the achievement of any particular competency level. Accordingly, they should be prepared for more successful teaching through the use of better approaches, exploration, as well as instruments for the extension of learning and teaching. The present Teacher Instruction Manual will give teachers right throughout the country the courage to effect a visible change in the teacher’s role and prevent their becoming inactive in the presence of new approaches. Similarly, we expect to award certificates and provide numerous development opportunities to teachers who go beyond the activities to involve themselves in the innovation of novel creations. What teachers have to do order in to become eligible to the awards is to improve these activities, using their creative thinking, and present them. Learning-teaching plans prepared in this manner outside the basic activity plan, should be forwarded to Assistant Director General ( Curriculum Development ), Science and Technology faculty, National Institute of Education, Sri Lanka. Selection of those entitled to awards will be made subsequent to the study of these activities by the relevant subject committees. We have endeavoured in this manner, to bring learning-teaching assessment and evaluation on to the same platform through new methodologies. According to this, teachers will be provided substantial latitude to meaningfully handle the learning-teaching process, school-based assessment, as well as assignment of home-work. It is our firm conviction that the school system of Sri Lanka will, make maximum use of this aid and depart from orthodox learning-teaching approaches to enhance the thinking abilities, social abilities as well as the individual abilities of the sons and daughters of the county. Dr. Indira Lilamani Ginige Assistant Director General (Curriculum Development), Faculty of Science and Technology , National Institute of Education, Sri Lanka. vi
  7. 7. Direction: Prof. J W Wickremasinghe - Director General Guidance: Dr. I. L. Ginige Assistant Director General Faculty of Science and Technology National Institute of Education Supervision : Mr. C M R Anthony Director Department of Science, Health & Physical Education Instructional leadership, Co-ordination and Editing : Mr. C M R Anthony - Director Mr. G H Gauthamadasa - Chief Project Officer Mr. W A D Rathnasuriya - Chief Project Officer Mr. W A Sumathipala - Project Officer Ms.J Athamlebbe - Project Officer Mr. A D A de Silva - Project Officer Mr. L K Waduge - Project Officer Mr. P Malavipathirana - Project Officer Ms. Nadee Ama Jayasekera - Project Officer Ms. H M Mapagunaratne - Asst. Project Officer Translation : Mr. R.B.A.Jayasekara Computer page setting : Mr. K.Wimalasena, Mahinda College, Galle. Art : Ms. U L N Fernando Teacher Service, Sirimavo Bandaranayake BV. Colombo.07. Cover page and pictures : Master. Soraj Dhananjaya Kolonne, Grade 11, Thurstan College, Colombo. vii
  8. 8. Contents Page ² Director General’s Message iii ² Preface iv ² Contributors vi ² Contents vii ² School Policies and Progammes 15 · Learning-Teaching Methodology Copyright © 2007 National Institute of Education - Sri Lanka. All rights reserved. ² Introduction 18-20 ² Quality Inputs 21 ² Activity Continuum 22-114 · Assessment and Evaluation ² Introduction 117-118 ² Tools for Extended Learning 119 -124 ² Prototype Questions 125 -129 viii
  9. 9. Competency 1.0 ( Investigates Scientific findings about structure of matter and quantity Competency level 1.1( Discuss the scientific findings about the structure of atom. Activity 1.1 ( Let us go inside the atom. Time ( 120 minutes Quality inputs ( ² Photograph of a nuclear reactor.annex 1.1.1 ² Three copies of instructions for exploration given in annex 1.1.2 • ² Three copies of the article"Let us get inside Copyright © 2007 National Institute of Education - Sri Lanka. All rights reserved. the atom"annex 1.1.3 ² Demy papers and pastels Teaching-learning process ( Step 1.1.1 ( ² Display the photograph to the class. ² Inquire from the children as to what know about what is given in the picture ² Conduct a brain storming discussion to highlight the following. That, ² In an atomic reactor,the energy in the atoms is transformed into energy that is useful to man. ² atom is the building blocks of matter. ² The findings about the atom can be made use of for the benefit of man. (15 minutes) Step 1.1.2 ( ² Divide the class into three groups. ² Provide the groups with copies of instructions for exploration. ² Assign the tasks and engage the groups in exploration. ² Prepare them to present their findings to the class. (60 minutes) Step 1.1.3 ( ² Get each group to present their findings to the class. ² Give the first opportunity to the respective group to elaborate on the presentation. ² Get the other groups to propose constructive sugges tions, ² Elaborate highlighting the following points. 9
  10. 10. That, ² Atom is a particle with a small mass. ² Fundamental sub atomic paticles inclued in an atom are electrons,protons and neutrons. ² Out of the paticles the lightest particle is the electron. ² mass of an electron is about 9.1095x 10-31 kg ² electron is a particle with a negative charge. ² Scientists J.J Thompson,Millikan Cotributed to the fundamental studies about the electron . ² Proton is a partical having a mass of about 1840 Copyright © 2007 National Institute of Education - Sri Lanka. All rights reserved. times the mass of an electron. ² Mass of a proton is about 1.6725x10-31kg ² Proton is a particle with a positive charge. ² Proton is symbolised as 11p ² Ernest Rutherford contributed to the fundamental studies about the proton. ² Neutron is a partical which has a mass almost equal to that of a proton. ² Mass of a neutron is about 1.6750x10-20 kg. ² Neutron is a particle with no charge,it is neutral. ² Neutron is symbolised as 10n ² The number of electron or the number of protons in an atom of an element is identical to that element. ² According to J.J Thompasons"Plum pudding "model he stated that an atom is a sphere which is positively charged,and the electrons which are negatively charged are embeded in it. ² According to Rutherford solar model the protons,and neutrons are collected at the centre which is the nucleus and the electrons are moving in orbits around it. ² These shells are named as K.L.M.N from centre out wards (45 mts) 10
  11. 11. Criteria for assessment and evaluation ² Names and describe the fundamental sub atomic particles. ² Appreciates that scientists have contributed to the findings about the atomic structure. ² Compare different atomic models. ² Collect data about scientific discoveries using references. ² Present fact in an alternative way. Annex 1.1.1 Copyright © 2007 National Institute of Education - Sri Lanka. All rights reserved. a 11
  12. 12. Annex 1.1.2 Instructions for group exploration ² Given below are three types of sub atomic particles in an atom. ² Electron ² Proton ² Neutron ² Focus your attention on the sub atomic particle relevant to you. ² With reference to the reading material provided to you discuss the follwing about the sub atomic particle relevant toyou. ² It`s discovery Copyright © 2007 National Institute of Education - Sri Lanka. All rights reserved. ² Properties ² How it is placed in the atom according to different atomic models. ² Be prepared to present your findings to the class. Annex 1.1.3 Let us go inside the atom Atom is derived from the Greek word "atomos" which means ,not divisible further but later it was discovered that it is made up sub atomic particles.Although there are many Sub atomic particles only three important particles are mentioned below. 1& Electron In the middle of the nineteenth century Scientists drew their attention whether it is possible to conduct through gases In 1875 B.C Crooks observed that in a closed glass tube with ends having two electrodes and a high voltage is applied and in the meantime the air pressure inside to tube is gradually reduced,there is a glow near the cathode.Further he noticed that if the air pressure is further reduced this glow gradually move from the cathode towards the anode,and that there is a"shadow" between the cathode and the anode.When the pressure inside the tube is about 1 pascall he noticed that the shadow got distributed throughout the tube and that there is an emission of a beam of rays from the cathode to the anode.Since these rays were emitted from the cathode they were named as cathode rays by crooks.This set up is called the cathode ray tube. In (1858BC-1940BC) J.J.Thompson conducted further experiments with these rays,As a result of these experiments following conclusions were arrived at about the prop- erties of cathode rays. 1 Cathode rays move in straight lines. 2 They are negatively charged 3 They are made up of particles having a mass. 12
  13. 13. J.J.Thompson conducted an experiment to determine the (e/m ) ratio of the cathode ray particales, where (e) is the charge and (m) is the mass. The value he got for e/m was very large e/m=1.76x10 c kg-1 The values obtained for e/m ratio for the cathode rays using different gases and different cath- odes is the same.By this Thompson concluded that the cathode rays consists of the same particles.Further Thompson stated that,the fundamental unit of electricity,the electron introduced by J.J. Stony in 1874 B.C.is the negatively charge particles in the cathode rays. Electron is a common sub atomic particle present in all atoms. Charge of an electron = 1.602x10-19 C Mass of an electron = 9.1095x10-31 kg At present different forms of cathode ray tubes are used in various electronic instruments. Some of these are TV photo tube,Computer monitor,Cathode ray Oscilloscope, Copyright © 2007 National Institute of Education - Sri Lanka. All rights reserved. Fluorescent tube High Voltage Cathode Anode To Vaccum Pump Simple Cathode Ray Emitting Tube Proton In 1886 B.C. E.Goldstien observed that when using a porous Cathode,is subjected to a voltage from 20,000V to 50,000V some special rays were seen to emit from the pores in the Cathode in a direction opposite to the Cathode rays.He named them as positive rays. When ratio e/m was calculated for the particles in these positive rays it was found that the value is numerically smaller to that of the particles in the cathode rays. When different gases were used in the Cathode ray tube the e/m ratio for the particles in the possitive rays were found to be whole numerical multiples of the e/m ratio for the particles in the possitive rays.When Hydrogen gas is used in the cathode ray tube.In short the lightest possitive rays particles were obtained from Hydrogen.In 1871 B.C-!937B.C Rutherford,named this lightest possitive ray particle as proton and also that it should be the common possitively charged funda- mental particle of all matter. Charge of a proton=1.602x10-19C Mass of a proton=1.6726x10-27 Kg Mass of a proton is 1840 times the mass of an electron. 13
  14. 14. High Voltage Anode Cathode with a slit production of possitive rays Neutron Possitively charged particles named α particles are emitted from radio active sources.When fall on to the instrument to detect charged particals, it causes a deflection.(Fig. a) In 1932 James Chadwick conducted an experiment form which it was founded that when a thin Berylium sheet was place in between the radio active source and the detector no deflection was seen ( Fig. b) When a paraffin sheet was place between the Berylium sheet and the detector tere was a α deflection. (Fig. c) Source of Detector particals Shows deflection (a) Possitive charge particals fall on detector Berylium plate No deflection is shown (b) charged particals are not falling on the Berylium plate Paraffin wax plate detector Shows a deflection (c) charged particals fall on the detector particals Chargeless Neutrons Particals with possitive charge (d) 14
  15. 15. Chadwick showed that when α Particles strikes the beryllium sheet it releases particles which has no charge.When these particles strikes the paraffin sheet,it releases charged particles and as a result there is a deflection in the detector.(Figd) He also found that when particles strikes the beryllium sheet,the uncharged particles emitted from it has a mass equal to that of the Hydrogen atom. He stated that these particles are another type of sub atomic particles and named them as neutrons. mass of a neutron = 1.6750x10-27 kg Thompsons` Atomic Model(Plum pudding model) Copyright © 2007 National Institute of Education - Sri Lanka. All rights reserved. α Rutherford`s model of the atom(Solar model) s Using rays emitted by radioactive material,in 1911 Geiger and Marsden conducted an experiment to find the στρucture of matter under the direction of Rutheford.Here a beam of particles was obtained using radio active polonium kept in a lead chamber with a slit.In this experiment a thin gold foil was bombarded with particles.They kept a screen painted with Zinc sulphide to detect the direction in which the particles move.There was a glow when particles struck the Zinc sulphide sheet. Rutherford's gold leaf experiment Source of Polonium Zinc Sulphide screen which could move around the gold leaf Thin gold leaf Led block with the hole 15
  16. 16. In this experiment it was discovered that most of the Alpha particals went through the gold foil without any deviation, a small number of Alpha particals deviated when going through the gold foil and a very small number were reflected. The reason why most of the Alpha particals went through without any difficulty was because according to Rutherford a major part of an atom is empty space. Atom α particals Nucleis Copyright © 2007 National Institute of Education - Sri Lanka. All rights reserved. particals not diverging Reflected particals particals diverging Model to explain the results of Rutherfords experiment α Further according to Rutherford possitively charged particles some deviated and some reflected because there are small areas inside atom where possitive charges are collected together.These possitively charged areas he called nucleui.Later Rutherford Put forward a theory according which he says,electrons are revolving in circular orbits around the nucleus,like the planets are revolving round the sun. electron nucleus path 16
  17. 17. Competency 1.0 ( Investigates Scientific findings about structure of matter and quantity Competency level 1.2 ( Use Scientific Conventions to highlight diversity in atoms Activity 1.2 ( Let us Investigates about atoms, make models, study about diversity. Time ( 120 minutes Quality inputs ( ² Poster showing the planetary modle structure of Helium and Sodium included in annex 1.2.1 ² Four copies of instructions for exploration given in Copyright © 2007 National Institute of Education - Sri Lanka. All rights reserved. annex 1.1.2 ² Four copies of the article"Looking at an atom with an exploratory eye", included in annex 1.2.3 ² Beads of three colours or small rigifoam balls.,bucket wires,gum,ekle and thread ² Demy papers and pastels Teaching-learning process ( Step 1.21 ( ² Display to the class the poster showing the structure of Helium and Sodium atoms. ² Conduct a brain storming session to highlight the following.facts. That, ² The shells in an atom from nucleus outwards are named K, L, M, N ² Helium atom has two electrons in the K shell Sodium atom has K, L, M, Shells with 2,8,1 electrons respectively. • ² The highest number of electrons K,L,M,N shells could have is 2, 8, 8,18 ² The arrangement of electrons in the shells around the nucleus of an atom is called electronic configuration ² The electronic configuration of an atom is one convention which indicate the identify of an atom. (15 minutes) 17
  18. 18. ² Provide the class with copies of instructions for exploration.material for making models,the letter,demy paper and pastel ² Assign the tasks and engage the groups in exploration. ² Prepare them to present their findings to the class. (60 minutes) Step 1.2.3 ( ² Get each group to present their findings to the class. ² Give the first opportunity to the respective group to elaborate on the presentation. ² Get the other groups to propose constructive sugges tions, ² Elaborate highlighting the following points. Copyright © 2007 National Institute of Education - Sri Lanka. All rights reserved. That, ² In Chemistry there are 110 elements discovered at present. ² Every elements is symbolized using the letters in the English Alphabet. ² Atomic number is the number of protons in the nucleus of the atom. ² In a neutral atom the number of electrons(- charges)and the number of protons (+chargs) are equal. ² In the atomic nucleus both types of sub atomic particles,protons and neutrons are present. ² In an element the number of protons is constant. But there are atoms with varying number of neutrons. ² The total number of Protons and neutrons in the nucleus of the atom is called the mass number or the number of nucleons. ² Atoms of an element having identical number of protons but different number of neutrons the mass number varies.These atoms are called isotopes. ² In a chemical symbol of an atom on the top left side is the mass number and at bottom is the atomic number. ( 12C ) 6 ² The relative mass of an atom is the number of times the mass of the atom relative to 1/12 of the mass of 12 6C isotope atom. 18
  19. 19. ² Relative atomic mass=mass of an atom of an element/massof 12 6C isotope atomx 1/12 (45 minuts) Criteria for assessment and Evaluation ² Names and describe conventions related to identification of elements. ² Appreciates that diversity of matter is built on diversity of atoms. ² Contruct models to show the structure of atoms. ² Show diversity by using Symbols. ² Discover facts using various Sources. Copyright © 2007 National Institute of Education - Sri Lanka. All rights reserved. Arrangement of sub - Atomic particals in Helium and Sodium He Atom ² K Shell Electronic configuration 2 ² Na Atom ² K Shell ²² ² ² ² ² L Shell ² M Shell ² ²² Electronic configuration 2" 8" 1 19
  20. 20. Annex 1.2.2 Instructions for group exploration ² Focus your attention to the six atoms assigned to your group, according to the table given below. Data of some atoms Symbol A B C D E F G H I J K L MNO P QR S T UV WX (not the standard ) Number of Protons 1 4 1 12 17 19 2 6 7 13 6 18 3 8 11 8 15 20 5 9 10 14 10 16 Copyright © 2007 National Institute of Education - Sri Lanka. All rights reserved. Number of 1 4 1 12 17 19 2 6 7 13 6 18 3 8 11 8 15 20 5 9 10 14 10 16 Electrons Number of 1 5 2 12 18 20 2 6 7 14 7 22 4 8 12 9 16 20 6 10 10 1412 16 Neutrons Group i Group ii Group iii Group iv ² Using data given in the table and the artical " Looking at the atom with an exploratory eye" find the standard chemical symbols to the elements provided to you. ² Find the atomic mass and mass number of the atoms provided to you by using the types of sub atomic particals and their numbers. ² Develope the eletronic configuration of the respective elements by writing the number of eletrons in the cells from closer to the nucleus outwards. ² Develope using the letter discuss about isotopes and relative atomic mass and find out the facts. ² Select necessary item from the common table and construct solar models of atoms allocated to you. ² Be prepared to present constructions and findings to the class. 20
  21. 21. Annex 1.2.3 "Looking at an atom with an exploratory eye" Do you know that all matter solids, liquids and gases found in your environment is formed by 110 elements getting grouped together in different ways ? Each of these elements are formed from building units called atoms.Although it is not possible to look at an Atom or its interior using the naked eye, the way the scientists by performing varius experiments have been able to learn about the structure of these is amazing. To begin with let us find about the sub atomic particals of atoms. Sub Atomic Particals Element Symbol Number of Number of Num,ber of Copyright © 2007 National Institute of Education - Sri Lanka. All rights reserved. Electrons Protons Neutrons Hydrogen H 1 1 -- Helium He 2 2 2 Lithium Li 3 3 4 Berelium Be 4 4 5 Boron B 5 5 6 Carbon C 6 6 6 Nitrogen N 7 7 7 Oxygen O 8 8 8 Fluorine F 9 9 10 Neon Ne 10 10 10 Sodium Na 11 11 12 Magnesium Mg 12 12 12 Aluminium Al 13 13 14 Silicon Si 14 14 14 Phosparous P 15 15 15 Sulphur S 16 16 16 Chlorine Cl 17 17 18 Argon Ar 18 18 22 Potasium K 19 19 20 Calcium Ca 20 20 20 Every element has a chemical symbol denoted by letters in the English alphabet. For easy study it is possible to arrange the number of ptotons in the atomic nucleus of all the elements found in the world. Now let us find out some theories about atoms. 21
  22. 22. Data of Elements of atomic numbers 1 - 20 Number of Electrons in the Name of Chemical Atomoc shells Mass Relative Element Symbol Number (Electronic configuration) number Atomic mass K L M N Hydrogen H 1 1 1 1 Helium He 2 2 4 4 Copyright © 2007 National Institute of Education - Sri Lanka. All rights reserved. Lithium Li 3 2 1 7 6'9 Beralium Be 4 2 2 9 9 Boron B 5 2 3 11 10'8 Carbon C 6 2 4 12 12 Nitrogen N 7 2 5 14 14 Oxygen O 8 2 6 16 16 Fluvorin F 9 2 7 19 19 Neon Ne 10 2 8 20 20'2 Sodium Na 11 2 8 1 23 23 Magnisium Mg 12 2 8 2 24 24'3 Aluminium Al 13 2 8 3 27 27 Silicon Si 14 2 8 4 28 28'1 Phosporus P 15 2 8 5 31 31 Sulphur S 16 2 8 6 32 32'1 Clorine Cl 17 2 8 7 35 35'5 Argon Ar 18 2 8 8 40 40 Potasium K 19 2 8 8 1 39 39'1 Calsium Ca 20 2 8 8 2 40 40'1 22
  23. 23. Atomic Number The atomic number of an element is the number of protons in the atom of that element.(In a neutral atom the number of protons in the nucleus is equal to the number of electrons in the shells.) Mass number The mass number of an element is the sum of the protons and neutrons in the atomic nucleus of that element, Relative atomic Mass You could understand that atoms are particles having a very small mass hence it is not useful in Chemistry to use the international unit of mass,the kilogram in relation to the mass of an atom. Hence the mass of an atom is stated as a relative value of a standard unit.It is called the Relative atomic mass unit. 12 Relative atomic mass Unit = mass of 6 C Isotope atom 12 The relative atomic mass of an atom is the number of times the mass of that atom in relation to the relative atomic mass unit.It could be stated as Relative atomic mass = mass of an atom atomic mass unit Relative atomic mass = mass of an atom of an element 12 mass of an atom of 6 C isotope x 1/12 There are differences between the atoms of the same element.An example of this is the presence of atoms of elements with same number of protons but with different number of neutrons,Such elements where the number of protons in the atomic nucleus is the same but the number of neutrons vary,and as a result they vary in their mass number.These are called isotopes. A Symbol is used to identify an atom.In an atomic symbol at the top left is the mass number 12 and at the bottom is the atomic number( 6 C) 23
  24. 24. Annex 1.2.6 Data about some of the isotopes found in nature of some elements Name of Atomic Mass Symbol of Number of Number of Number of element number number the isotope protons Neutrons Electrons in the in the in the nucleus nucleus nucleus Hydrogen 1 1 1 H 1 0 1 1 1 2 2 1 H 1 1 1 1 3 3 1 H 1 2 1 3 Helium 2 3 2 He 2 1 2 2 4 4 2 He 2 2 2 Lithium 3 6 6 3 Li 3 3 3 3 7 7 Li 3 4 3 3 10 Boron 5 10 5 B 5 5 5 5 11 11 5 B 5 6 5 Carbon 6 12 12 6 C 6 6 6 6 13 13 C 6 7 6 6 14 Nitrogen 7 14 7 N 7 7 7 7 15 15 7 N 7 8 7 16 Oxygen 8 16 8 O 8 8 8 17 8 17 8 O 8 9 8 8 18 18 8 O 8 10 8 20 Neon 10 20 10 Ne 10 10 10 21 10 22 10 Ne 10 11 10 10 22 22 10 Ne 10 12 10 Sulpher 16 32 32 S 16 16 16 16 16 33 33 S 16 17 16 16 16 34 34 S 16 18 16 16 24
  25. 25. Chlorine 17 35 35 Cl 17 18 17 17 17 37 37 Cl 17 20 17 17 39 Potasium 19 39 19 K 19 20 19 19 40 40 19 K 19 21 19 19 41 41 19 K 19 22 19 40 20 40 Ca 20 20 20 Calcium 20 42 20 42 20 Ca 20 22 20 43 20 43 20 Ca 20 23 20 44 20 44 20 Ca 20 24 20 46 20 46 20 Ca 20 26 20 48 20 48 20 Ca 20 28 20 25
  26. 26. Competency 1.0 ( Investigates Scientific findings about the structure of matter and quantity. Competency level 1.3 ( Explain the Properties of compounds using it`s bonds. Activity 1.3 ( Let us Investigates the Properties of compounds using it`s bonds. Time ( 120 minutes Quality inputs ( ² Atomic models arranged according to instructions in annex 1.3.1 ² Two copies of instructions for exploration given in Copyright © 2007 National Institute of Education - Sri Lanka. All rights reserved. annex 1.3.2 ² Two work stations arranged according to instructions given in annexe 1.3.3 ² Two copies of the article "Chemical bonds" given in annex 1.3.4 ² Demy papers and pastels Teaching-learning process ( Step 1.3.1 ( ² Join the atomic models accordingly with the help of the students. ² Lead a discussion highlighting the following points. ² Bonds are formed between atoms by the electron. ² Two electrons join to form a bond between two atoms. ² When a chemical bond is formed ,the atoms that go to form the bond behave the following fashion. ² One atom donates an electron from its last energy level to the other atom. ² The election donated by one atom is accepted by the other atom. ² The positive ion formed by the donation of the eletron and the negative ion formed by the acceptance of electron are attracted. ² When there is no formation of ions,electron pairs are shared between two atoms ² During the formation of bonds the atoms try to achieve the maximum inert gas configuration.
  27. 27. . ² An atom reach the maximum nobel gas configuration by forming one or more bonds. ² Molecules are formed by atoms joining together by chemical bonds. ² A molecules consists of two or more atoms which may be homogeneous or heterogeneous. ² When chemical bonds form between heterogeneous atoms compounds are formed. ² It is possible to develop the chemical equation of a com pound by indicating the different number of atoms in a Copyright © 2007 National Institute of Education - Sri Lanka. All rights reserved. compound molecule using the symbols of elements. (15 mts) Step 1.3.2 : ² Divide the class into two groups. ² Provide the groups with instruction for exploration the article,demy papers and pastel. ² Assign the tasks and engage the groups in exploration. ² Prepare them to present their findings to the whole class. (60 mts) Step 1.1.3 (² Get each group to present their findings to the class. ² Give the first opportunity to the respective group to elaborate on the presentation. ² Get the other groups to propose constructive suggestions, ² Elaborate highlighting the following points. That, ² Atoms of elements by releasing electrons become positive ions,and by receiving electrons become negative ions. ² The positive ions are named cations and the negative ions as anions. ² There are ions which are formed from a single atom or from a number of atoms. ² Oppositely charged ions are attracted together and thereby forming ionic bonds, ² When ions get together to form a compound,the arrange ment of ions in space is called the ionic lattice.

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