Pure Chem S4 Notes (BT 2020) - Final Update 2 Jun 2022

Pure Chemistry Notes 1 PURE CHEMISTRY NOTES 2020 © SEC 4

Pure Chemistry Notes 2

Pure Chemistry Notes 3 4EXP CHEMISTRY TOPICS No. Topics Page Remarks 1 Periodic Table 4 2 Rate of Reaction 18 3 Redox Reaction - Oxidation & Reduction 36 4 Energy - Exothermic & Endothermic Reactions 44 5 Electrolysis 57 6 Air 78 7 Harber Process 90 8 Organic Chemistry - Petroleum & Alternative Sources of Fuel 94 9 Organic Chemistry - Alkanes 99 10 Organic Chemistry - Alkenes 103 11 Organic Chemistry - Alcohols 109 12 Organic Chemistry - Carboxylic Acids 114 13 Organic Chemistry - Esters 117 14 Organic Chemistry - Addition Polymers 126 15 Organic Chemistry - Condensation Polymers 131

Pure Chemistry Notes 4 Periodic Table The Periodic Table is an arrangement and classification of the elements. It can be used to predict the properties of elements from trends that are observed. GROUP (Vertical Column) • Vertical columns of elements in the Periodic Table • The Group number indicates the number of valence electrons in an atom of an element. • Element in the same group have the same number of valence electrons, hence they form ions of the same charges and have similar chemical properties (reaction) Element Electronic Configuration Valence electrons Group Ions Lithium 2.1 1 I Li+ Sodium 2.8.1 1 I Na+ Potassium 2.8.8.1 1 I K+ Oxygen 2.6 6 VI O2- Sulphur 2.8.6 6 VI S2- Beryllium 2 2 II Be2+ Magnesium 2.8.2 2 II Mg2+

Pure Chemistry Notes 5 Exception Element Electronic Configuration Valence electrons Group Helium 2 2 0 Helium is not located in Group II, as its 1st shell is completely full and it has a stable noble gas configuration. Trends down a Group The following trends are observed when down a Group: • The proton number becomes bigger. The number of energy levels increases as you move down a group as the number of electrons increases. Each subsequent energy level is further from the nucleus than the last. Therefore, the atomic radius increases as the group and energy levels increase. • The properties of the elements become more metallic. This is because on going down the group, the elements lose electrons more easily, as the valence electrons become spaced further away from the positive nucleus. PERIOD (Horizontal row) • Horizontal rows of elements in the Periodic Table. • The Periodic Table is a list of elements arranged in order of their increasing atomic or proton number • The Period number indicates the number of occupied electron shells in an atom of an element.

Pure Chemistry Notes 6 Trends across a Period ▪ Across the period, elements changes from Metals to Non-metals ▪ A decrease in metallic properties ▪ An increase in non-metallic properties ▪ This results in the different types of oxides formed. Group I II III IV V VI VII 0 Symbol Na Mg Al Si P S Cl Ar Properties Metallic Metalloid (Elements having the properties of both metals and non- metals) Non-metallic Nature of oxide Basic oxide Amphoteric oxide Acidic oxide • The atomic radius decreases. As you go across a period, electrons are added to the same energy level. At the same time, protons are being added to the nucleus. The concentration of more protons in the nucleus creates a "higher effective nuclear charge." In other words, there is a stronger force of ‘positive attraction’ pulling the electrons closer to the nucleus resulting in a smaller atomic radius. • The electronegativity increases (electronegativity is a measure of the ability of an atom or molecule to attract pairs of electrons in a chemical bond.) • The tendency for an element to gain electrons to form negative ions, increases across the period. Decreasing metallic properties Increasing non-metallic properties

Pure Chemistry Notes 7 Difference in Chemical properties between Metals Non Metals Forms basic oxides Forms acidic oxides (or neutral oxide like H2O, CO) Tend to lose electrons to gain a positively charged ion Tend to gain electrons to form a negatively charged ion Difference in Physical properties between Metals Non Metals Good conductor of heat and electricity Poor conductor of heat and electricity Generally malleable, ductile Generally brittle if solid Solid at room temperature (except Mercury) Generally liquid or gas at room temperature, they can exist as solids too. ▪ The metallic elements between Gp II and III are known as the Transition Metals Transition metals have: ▪ High electrical conductivity due to delocalized/free flowing electrons ▪ Varied oxidation states eg. Fe2+, Fe3+, Cu+, Cu2+ ▪ Formed compounds that are coloured. Compound Colour Compound Colour Iron (II) hydroxide Green Copper (II) oxide Black Iron (III) hydroxide Brown Copper (II) carbonate Green Iron (III) chloride Yellow/Orange Copper (II) sulfate Blue Potassium Manganate (VII) Purple Manganese (IV) oxide Black

Pure Chemistry Notes 8 GROUP I: ALKALI METALS Physical properties of Group I • Shiny and silvery in appearance when freshly cut • Are soft can be cut easily with a knife • Good conductors of heat and electricity • Have low melting and boiling point (compared to other metals) – Mp & Bp decreases down Gp I • Have low densities (eg. Li, Na and K can float on water) – Density Increases down Gp I Chemical properties of Group I • Have one electron in its valence shell. Hence similar chemical properties • Highly reactive metals - Reactivity increases down the group • Soluble in water to form alkalis Group I metals + H2O → Metal hydroxide + Hydrogen gas 2Li (s) + 2H2O (l) → 2LiOH (aq) + H2 (g) 2Na (s) + 2H2O (l) → 2NaOH (aq) + H2 (g) (Violent rxn) 2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g) (Violent rxn) • React readily with oxygen in air to form basic oxides 4Na (s) + O2 (l) → 2Na2O (s) The basic oxides formed from Group I metals can further dissolve in water to give alkaline solution. Alkaline solution will turn red litmus blue and universal indicator purple Na2O (s) + H2O (l) → 2NaOH (aq) Hence, these reactive metals and are stored in oil to prevent itself from reacting with air and moisture.

Pure Chemistry Notes 9 • Alkali metals are powerful reducing agents as it loses it valence electrons easily to attain a stable noble gas structure. Li - e → Li+ Na - e → Na+ K - e → K+ Trend in Chemical Properties of Group I Down Group I, the reactivity and reducing power of the metals increases. Reason: As size of atom increases, ease of losing electrons from bigger atoms increases. In the larger atoms, the valence electron is further away from the nucleus. The nuclear charge holding the valence electron to the atom is weak. Hence it is more easily lost. Compounds of Group I • Ionic compounds - Lattice structure • Soluble in water - Alkali (Universal indicator will turn purple) • Similar chemical formula Element Chloride Hydroxide (Alkali) Sulfate Li LiCl LiOH Li2SO4 K KCl KOH K2SO4 Rb RbCl RbOH Rb2SO4

Pure Chemistry Notes 10 GROUP VII: HALOGENS Physical properties of Group VII • Have low melting point and boiling points - bp and mp increases down the group. • Are coloured - The colour of the halogen becomes darker down the group. Element Colour State at room temperature F2 Pale yellow Gas Cl2 Greenish yellow Gas Br2 Reddish brown Liquid I2 Purplish black Solid At2 Black Solid Chemical properties of Group VII • Are reactive non-metals - They are also said to be electronegative as they have a high tendency to gain an additional electron in its valence shell to achieve a more stable octet configuration. They do so by sharing an electron (in the formation of covalent compounds) or by accepting an electron (in the formation of an ionic compound). • Halogens reacts with most metals to form salts called halide