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6243320-775237IGCSE (Edexcel) Chemistry 00IGCSE (Edexcel) Chemistry Topic 1: The states and the structure of matterObjectiveNumberobjectivesStudents will be assessed on their ability to……….RecommendationsText book11.1understand the arrangement, movement and energy of the particles in each of the three states of matter: solid, liquid and gasStudents should first understand the term ‘matter’ and have some idea of the minute size of particles with indirect evidence for their existence showing matter to be ‘discontinuous’. The properties of each of the three states to know are shape, density and compressibility. It is important to know that it is the different strengths of attractive forces between particles that determine the state of a substance at a given temperature. The closeness of particles to each other is almost the same in solids and liquids which explains that neither is compressible. However, in liquids the forces are too weak to prevent movement and in solids they strong enough to allow only vibration about a fixed point. The distances between particles in a gas are much greater than the size of the particles themselves allowing a lot of compressibility. Many examples of solids, liquids and gases should be known EC 121.2understand how the interconversions of solids, liquids and gases are achieved and recall the names used for these interconversions.Heat energy is transformed into vibrational and then kinetic energy as a solid changes to a liquid and then a gas. The term ‘volatile’ and volatility should be understood so that low melting and boiling point means high volatility. The reverse of sublimation is often called deposition and an example of this process is shiny black crystals of Iodine subliming to purple vapour (which can be reviewed later when the halogens are discussed) or dry ice (solid carbon dioxide)EC 231.3explain the changes in the arrangement, movement and energy of particles during these interconversions.Cooling curves e.g. for cyclohexane or a heating curve e.g. for naphthalene show the idea of melting point/freezing point (and boiling point) as a plateau on the heating/cooling curves. Changes in kinetic and potential energy explain the shape of the graphs produced. Latent heat explains why a plateau is seen. Students must be able to use melting and boiling point data to predict the state of a specific substance at a particular temperature e.g. predict the state at room temperature (EC P5 Q3)EC 2-341.4describe and explain experiments to investigate the small size of particles and their movement including:i) dilution of coloured solutionsii) diffusion experimentsIf a dilute solution of potassium permanganate is first made and then progressively diluted, the colour of the solution will persist after several dilutions which illustrate the small mass (and size) of the particles.Students must be aware of the kinetic theory and define ‘diffusion’ with several experiments illustrating this e.g. the upward and downward diffusion of hydrogen and bromine, the slow diffusion of copper sulphate or potassium permanganate in water and the long glass tube experiment (EC P5 Q4) involving ammonia and hydrogen chloride gases. The slower diffusion in liquids should be explained and the reason for different diffusion rates of gases, depending on mass of particles and temperature.(EC P5 Q5)EC 3-551.5understand the terms atom and moleculeThe word particle is a generic term and students should know that the atom is the smallest type of particle that can exist independently with molecules being those of either elements or compounds. EC 2961.6understand the differences between elements, compounds and mixturesThe important definitions and fundamental ideas such as the definition of the terms ‘element’, ‘ compound’, ‘simple mixing and separation’ and ‘chemical combination’ should be known. Students will already be familiar with many elements and their symbols as well as some formulae.EC 30-3271.7describe experimental techniques for the separation of mixtures, including simple distillation, fractional distillation, filtration, crystallisation and paper chromatographyThis is largely a review of KS3 but the important principle of using differences in physical properties in order to separate substances should be known with examples of each of the techniques described. EC P97 Q2EC 89-9181.8explain how information from chromatograms can be used to identify the composition of a mixture. Students should be aware of the principles of chromatography, the choice of solvent and how to recover the separated dyes. EC P97 Q4EC 9191.9understand that atoms consist of a central nucleus, composed of protons and neutrons, surrounded by electrons, orbiting in shellsStudents should appreciate the atom as largely empty space and the unimaginable density of the nucleus. The term ‘subatomic particle’ should be used and the term ‘nucleon’ as any particle in the nucleus.EC 6-7101.10recall the relative mass and relative charge of a proton, neutron and electronThe electron mass is 1/1840 (approximately 1/2000) that of the proton and neutron. This means that one single proton (or neutron) has approximately the same mass as 2000 electronsThe charges of electron and proton are equal but opposite. This is important as their equal number then makes the atom neutral overall.EC 7EC 52111.11understand the terms atomic number, mass number, isotopes and relative atomic mass (Ar)Atomic number is also called ‘Proton number’ and should be defined and given in exam responses as the number of protons in the nucleus or in the atom. Mass number is also called the ‘Nucleon number’(EC P12 Q2) Isotopes have identical chemistry since the equal number of protons means an equal number of electrons in total and in particular in the valence (outer) shell. Physical properties vary e.g. density. (EC P52 Q4c)Several examples of isotopy should be known and especially that of hydrogen with its unique isotope with no neutrons.The relative atomic mass scale has the Carbon-12 isotope as its standard and since Ar is relative to (1/12 of) the mass of this isotope, it has no units.EC 7-8121.12calculate the relative atomic mass of an element from the relative abundances of its isotopesRelative atomic mass is the weighted average of the isotopic masses of an element relative to the mass of a C-12 isotope. The natural abundance is taken into account in the calculation and chlorine illustrates this well. At IGCSE level the periodic table usually shows Ar values rounded up or down to the nearest whole number, with Cl and Cu being exceptions. Students are sometimes required to calculate abundance from a given Ar value.EC 176-178, 226131.13understand that the Periodic Table is an arrangement of elements in order of atomic numberThe elements are not in order of Ar value as there are two positions where Ar decreases as atomic number increases. However the table is constructed on the basis of electron configuration which depends on the number of protons.EC 9, 226141.14deduce the electronic configurations of the first 20 elements from their positions in the Periodic TableStudents should know the names and symbols of the first twenty elements (and several others). The ‘2, 8, 8 rule’ only works for the first twenty elements (up to calcium). The outer shell is known as the ‘valence shell’.EC 8-9EC 99-100151.15deduce the number of outer electrons in a main group element from its position in the Periodic Table.The table was constructed such that elements with the same number of electrons in the outer (valence) shell are in the same vertical column or group (and have similar properties). The exception is Helium which has 2 electrons in the outer shell and is in group 8(0).EC 10-12EC 99-100162.1understand the terms group and periodVertical columns and horizontal rows. Hydrogen and helium form the first short period called period 1. There are three short periods 1-3. Only the main groups are numbered 1-8(0) and not the transition elementsEC 99-100, 226172.2recall the positions of metals and non-metals in the Periodic TableAt room temperature there are 88 solids, 11 gases and 2 liquids. Some new elements are unconfirmed and unstable. Most elements are metallic and on the left of the table. The diagonal step line separates them from the non-metals with metalloids on the border. There are many useful websites on the periodic table such as ‘web elements’ or ‘dynamic periodic table’ which are interactive. Students should always have an IGCSE exam periodic table at hand in class for quick reference.EC 99-100182.3explain the classification of elements as metals or non-metals on the basis of their electrical conductivity and the acid-base character of their oxidesThe classification is based on a set of physical properties such as melting point, appearance, malleability, ductility, density and conductivity of heat and electricity. This is a general classification and there are many exceptions e.g. sodium, mercury, lead, graphite etc. The metallic oxides are basic (and alkaline if soluble) and non-metallic oxides are acidic if soluble. EC P59 Q3EC 55-56EC 100192.19describe the reactions of carbon magnesium, and sulphur with oxygen in air, and the acid-base character of the oxides These three elements all burn in oxygen and their oxides can be tested for solubility and effect on U.I. (a review of the pH scale and UI colours is needed here). Rain water is naturally acidic due to carbon dioxide and increasingly acidic due to sulphur dioxide from burning of fossil fuels and other industrial pollution.EC 55-56202.4understand why elements in the same group of the Periodic Table have similar chemical propertiesThis will be illustrated later in this topic when groups 1 and 7 are studied in detail. The modern periodic table is arranged so that the number of valence electrons is the same for elements in the same group which therefore have similar properties. Student should not explain that similar properties arise because elements are in the same group!! It is because the number of valence electrons is the same. Helium is an exception with 2 valence electrons but is in group 8 becasue all Noble gases have full outer shells.EC 99212.5understand that the noble gases (Group 0) are a family of inert gases and explain their lack of reactivity in terms of their electronic configurations.This will be dealt with in detail in Topic 2 (chemical bonding). The word ‘inert’ means unreactive.EC 101222.6describe the reactions of the Alkali metals with water and understand that the reactions provide a basis for their recognition as a family of elementsAll have one valence electron giving them similar properties. Sodium properties and the reaction with water are a useful demonstration for the general properties of the Alkali metal family. The points to emphasise are storage in oil, easily cut and show a lustre which is rapidly tarnished. The sodium floats on water showing low density and melts to a molten ball of sodium as the reaction is exothermic. The molten balls of sodium will fuse if they meet. The ‘pop’ sound when using a lighted splint indicates hydrogen gas is produced and a yellow ‘halo’ of sodium vapour is seen. The resulting solution is strongly alkaline and turns UI purple. The word and balanced chemical equation for the reaction must be known.Similarities in the Alkali metals should be known and also the trends in softness (they become softer as we descend the group) and reactivity.The elements become denser as we descend the group and caesium can be seen to sink in water before exploding.EC 102232.7describe the relative reactivity of the elements in Group 1The elements become more reactive as we descend the group and observations when the solid elements are cut and tarnish and then placed in water, provides evidence for the trend. Lithium, sodium and potassium are stored in oil and rubidium and caesium are kept in argon atmosphere conditions in glass vials.EC 102-104242.8explain the relative reactivity of the elements in Group 1 in termsof distance between the outer electrons and the nucleus.Students should be aware that electron loss from the valence shell occurs (producing positive ions) as the metal reacts. The further away the electron is from the nuclear attraction, the easier it is to lose the electron and the more reactive the metal.EC 104252.9recall the colours and physical states of the Group 7 (the Halogens) elements at room temperatureThe halogens are typical non-metals, are toxic, volatile, diatomic elements and since the molecules get larger and attractive forces stronger as we descend the group, the elements become less volatile. Fluorine (pale yellow) and Chlorine (pale green) are both gases while Bromine is a dense red brown volatile liquid and Iodine a shiny black crystalline solid which sublimes to dense purple vapour.EC 105262.39describe a test for chlorine gasChlorine can be made by adding one drop of conc HCl to a few tiny crystals of potassium permanganate. Chlorine has a bleach-like smell of the swimming pool. The gas turns damp blue litmus paper white as it bleaches it and also slightly pink. Cl2 + H2O HCl + HOClThe solubility and bleaching ability decreases down the group.EC 93272.10make predictions about the properties of other halogens in this groupStudents should be aware that trends within the groups in both physical and chemical properties can be used to predict the properties of group members e.g. volatility or reactivity of the halogens. The properties of the rarest element on earth (Astatine) can be predicted from established trends.EC P111 Q3EC 108282.13describe the relative reactivity of the elements in Group 7The halogens become less reactive as we descend the group in contrast to the alkali metals which become more reactive.EC 107292.14describe experiments to demonstrate that a more reactive halogen will displace a less reactive halogen from a solution of one of its saltsDisplacement reactions using solutions of the halogens and solutions of the potassium halides. The mixture should be treated with hexane in order to identify the free halogen which is present after mixing. Students should be aware that hexane is less dense than water and immiscible with water. It is also a better solvent for a free halogen which is why the halogen concentrates itself in the organic layer and can be seen more easily. Word equations for these displacement reactions must be written.Students can subsequently predict the outcome of reactions involving fluorine and astatine.EC 107-109302.15understand these displacement reactions as redox reactions.This objective is not essential or tested here and will be covered in detail later. However, the idea of electron loss and gain, oxidation and reduction and oxidising and reducing agents, and net ionic equations illustrate the point and might be included by your teacher. EC 108 ................
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