Quick Revision notes V2.0 Science Chem (No organic)

‘O’ Level Science Chemistry By Hazel You Quick Revision Notes V2.0 http://www.thekimiyagroup.com 1 ‘O’ Level Science Chemistry Quick Revision Notes • To check purity of a substance – Determine melting or boiling points (the only method) Common Chemicals Common Name Chemical Name Common Name Chemical Name Limestone Calcium carbonate Lime / quick lime Calcium oxide Limewater Calcium hydroxide Aqueous Ammonia Ammonium hydroxide Colour of some substances Colour Substances Colour Substances White Group I, II and III, ammonium compounds, Anhydrous CuSO4 Black CuO (s), I2 (s) Shiny/grey Most metals Yellow PbI, AgI, hot ZnO, Fe3+ (aq) Blue Cu2+ salts Red-brown Br2(l), Copper Metal, Fe(OH)3 (s) Green Fe(OH)2 (s), some Cu2+ salts Fe2+ (aq), Cr3+ 1. Separation techniques Method Substance to separate Substance(s) obtained Concept behind method Remarks Filtration § Insoluble solid from a liquid. § Soluble solid & insoluble solid Filtrate Residue (Solid) § Different solubility in the liquid § Large insoluble solid trapped by filter paper Decanting Large insoluble solid from liquid. - § Large insoluble solid - Evaporate to dryness A soluble solid from a liquid. Dry / anhydrous salt § Different physical states § Not for solids that decompose on heating Crystallisation § A pure solid from an impure solid. § A soluble solid from a liquid. § Substances which decompose. Well-formed crystals of the pure solid (solute) § As temperature decreases, solubility decreases. § When saturated solution is cooled, crystals are formed. § For solids that decompose on heating § To retain water of crystallisation (hydrated salt) Sublimation A mixture of solids which one of them sublimes. Pure solid which sublimes. § One substance changes directly from solid to vapour on heating. § E.g. iodine, moth balls, dry ice. Simple distillation A solution of a dissolved solid (solute) in a liquid. Pure liquid as distillate. § Different physical states § Liquid is heated into vapour, cools and condenses into pure liquid in condenser and collected as distillate. Fractional distillation Mixture of miscible liquids Pure liquids as distillate. § Difference in boiling point § Uses a fractionating column. § Liquid with the lower bp will be distilled out first. Separating funnel Mixture of two immiscible liquids. Two separated liquids § Difference in densities § Mixture separates into two layers Paper chromatography Solution containing mixture of small amounts of solids Solutes separated in the chromatogram. § Different solubility of solutes in the solvent used § More soluble solutes travel a longer distance with solvent.

‘O’ Level Science Chemistry By Hazel You Quick Revision Notes V2.0 http://www.thekimiyagroup.com 2 2. Particulate Nature of Matter • Kinetic Particle Theory of Matter – Particles are too small to be seen directly – There are spaces between particles – Particles are in constant random motion; move in different speeds in different states – showed in Diffusion ◦ Rate of diffusion depends on molecular mass and temperature • Particulate models of matter in different state – Describes the arrangement and motion of particles Physical State Solid Liquid Gas Arrangement Orderly, closely packed Disorderly, closely packed Disorderly, far apart Motion Vibrate about fixed position Slide pass one another Free to move at high speeds in all direction • Temperature of a matter is due to the speed/kinetic energy of the particles within it. • Matter expands due to the increase in distance between its particles. • Matter may be coloured but its particles are not coloured. 3. Element, Compound and Mixture Element Compound Mixture Definition § Pure substance § Cannot be broken down into simpler substances by chemical means. § Pure substance § Contains two or more different elements chemically combined together. § Contains two or more substances that are not chemically combined together. Classification by... § Physical state § Periodic Table § Types of bonding (Covalent / Ionic / Both) § Mixture of elements § Mixture of compounds § Mixture of both elements and compounds. It can exist as… § Atoms (smallest unit) § Molecules (in covalent bonding) § Molecules (covalent compound) § Ions (ionic compounds) Composition § Fixed composition § Fixed composition of the elements by mass. § Variable composition. Melting and boiling points § Fixed § Fixed § Variable (A range of temperature) Properties § Own characteristic physical and chemical properties. § Physical and chemical properties are different from its elements. § Does not have its own properties. § Has same properties as its components. Formation - § Involves energy changes for chemical reaction to occur § Mixing with no energy required Separation § Cannot be separated or broken down further. § Cannot be separated by physical means. § Requires energy (usually involves decomposition) § Easily separated into its components by physical means without chemical reaction § Involves little or no energy

‘O’ Level Science Chemistry By Hazel You Quick Revision Notes V2.0 http://www.thekimiyagroup.com 3 4. Atomic structure Subatomic particle Symbol Relative mass Charge Proton p 1 1+ Neutron n 1 0 Electron e- 1 1840 1- • Atom – electrically neutral – equal no. of protons and electrons • Isotope – atom of the same element but with different no. of neutrons • Electronic configuration – shows the arrangement of electrons in an atom ***All atoms wanted to obtain a stable electronic configuration of a noble gas. Therefore, 1) Atoms of the same element react to form molecules (by sharing valence electrons), OR 2) Different elements react to form stable compounds (by gain or lose valence electrons OR share valence electrons) 5. Chemical Bonding, Structure and Properties Ionic Bonding Covalent Bonding Definition Strong electrostatic force of attraction between oppositely charged ions Bond formed by the sharing of at least one pair of valence electrons between atoms Formation of bond § By electron transfer from metals to non- metals § Metal atom loses e- while non-metals gain e- § By electron sharing among atoms § Non-metals share electrons § No. of pairs of shared e- = No. of covalent bonds Description of particles formed § Positive and negative ions § Simple ions/Polyatomic ions § Between atoms of same element § Between atoms of different elements (compound) Structure Giant Ionic Lattice § Large number of oppositely charged ions arranged in a repetitive, orderly manner, held in place by strong ionic bonds Simple Molecular Structure § Small molecules § Strong covalent bond within molecule § Weak intermolecular forces of attraction between molecules Dot and cross diagrams to show bonding Ionic Bonding (MgCl2) Covalent bonding (CO2) Giant Ionic or Crystal Lattice Simple Molecular Structure C O O Mg 2+ - Cl - Cl + 1 2 3 4 For 1st 20 elements Aft er t he 20th element, 3rd shell can actually hold up to 18 electrons Max 2 Max 8 e- Max 8 e-

‘O’ Level Science Chemistry By Hazel You Quick Revision Notes V2.0 http://www.thekimiyagroup.com 4 Physical Properties of Different Structures • Physical state / appearance depends on – type of bonding or attraction between particles in the substance – the arrangement of particles in the substance • Melting and boiling point depends on – amount of energy required to overcome attraction – type and strength of bonding or attractive forces to be overcome / broken • Volatility depends on boiling point • Solubility depends on whether the particles can / cannot attract the solvent