AY 2024 Sem 2 A106 L01 Lecture Notes PDF

OFFICIAL (CLOSED) \ NON- SENSITIVE A106 Organic and Inorganic Chemistry Lesson 01: Periodic Table I School of Applied Science  OFFICIAL (CLOSED) \ NON-...

OFFICIAL (CLOSED) \ NON- SENSITIVE A106 Organic and Inorganic Chemistry Lesson 01: Periodic Table I School of Applied Science  OFFICIAL (CLOSED) \ NON- SENSITIVE Contents Periodic Table Electron Configuration Atomic radius, ionic radius, 1st ionisation energy and electronegativity Group 2 elements and its compounds Group 17 elements and its compounds Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Section 1 Periodic Table Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Periodic Table (Recap) Group Non Metals Period Metalloid s Metals Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Periodic Table (Recap) Elements are arranged according to increasing atomic number Comprises of metals, metalloids and non-metals 7 horizontal rows or periods 18 vertical columns or groups Arrangement of elements in the periodic table is related to the electron configuration Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Periodic Table (Recap) Group 17: Group 1: Halogens Alkali Metals Transition Metals Lanthanoids Group Group 2: 18: Alkaline Earth Actinoids Noble Metals Gases Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Periodic Table (Recap) Group Common Name 1 Alkali Metals 2 Alkali Earth Metals 3-11 Transition Metals 17 Halogens 18 Noble Gases Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Information in Periodic Table Atomic Symbol Atomic number = Proton number = number of electrons in an atom  Determine the atom identity Relative atomic mass The ratio of the average mass of one atom of an element to one twelfth of the mass of an atom of carbon-12. The relative atomic mass is an average of the Name atomic masses of all the different isotopes in a sample, with each isotope's contribution to the average determined by how big a fraction of the sample it makes up. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Activity 1 Determine the number of protons, neutrons and electrons in the elements shown below. N = proton no. = 7, neutrons no. = 7 , electrons no.= 7 F = proton no.= 9 , neutrons no. = 10, electrons no. = 9 S = proton no. =16, neutron no. = 16, electron no. =16 Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Section 2 Electron Configuration Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Electron configuration Electron configuration refers to the distribution of electrons of an atom around a nucleus. For example, a carbon atom has 6 electrons  2 electrons are found in the 1st shell  4 electrons are found in the 2nd shell (valence shell) − − − − − − Electron configuration of carbon is 2.4 Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Electron configuration Due to electrons repulsion, there is a limit to the number of electrons that can be found in a shell. The maximum number of electrons found in each shell is given in the table below. Electron shell 1 2 3 4 Max no. of 2 8 18 32 electrons Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Electron configuration Electron configuration for the first 20 elements Element Atomic Electron Element Atomic Electron number configuration number configuration H 1 1 Na 11 2.8.1 He 2 2 Mg 12 2.8.2 Li 3 2.1 Al 13 2.8.3 Be 4 2.2 Si 14 2.8.4 B 5 2.3 P 15 2.8.5 C 6 2.4 S 16 2.8.6 N 7 2.5 Cl 17 2.8.7 O 8 2.6 Ar 18 2.8.8 F 9 2.7 K 19 2.8.8.1 Ne 10 2.8 Ca 20 2.8.8.2 Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Activity 2 Consider the element shown below. a) Write down the electron configuration. 2.8.8.2 b) Determine the number of electron shells and the number of valence electrons the element has. 4 electron shells and 2 valence electrons c) Determine the period and group the element is found in the periodic table. Period 4 Group 2 Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Section 3 Atomic radius, Ionic radius, 1st ionisation energy and electronegativity Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Trends in periodic table Across the same period, elements have same number of occupied electron shells increasing proton (atomic) numbers increasing number of valence electrons Down the same group, elements have same number of valence electrons increasing number of electron shells Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Atomic radius Atomic radius is the distance from the centre of the nucleus to the outermost shell containing electrons of an atom. − Atomic radius − − − − − Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Atomic radius Atomic radius trend H He 53 31 Li Be B C N O F Ne 167 112 87 67 56 48 42 38 Na Mg Al Si P S Cl Ar 190 145 118 111 98 88 79 71 K Ca Ga Ge As Se Br Kr 243 194 136 125 114 103 94 88 Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Atomic radius Atomic radius increases when moving down the group. Moving down the group, the elements Group 1 have same number of valence electrons, but the number of electron shells increases. Although the number of protons in nucleus increases, the electrons are further and shielded by more electron shells. As a result, the valence electrons are attracted less strongly to nucleus, and are not held so tightly and hence, the atomic radius increases. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Atomic radius Period 1 Atomic radius decreases when moving across the same period. Moving across the same period, the nuclear charge becomes more positive as the number of protons in the nucleus increases. Although the number of electrons also increases, the outermost electrons are in the same electron shell and hence experience relatively similar shielding effect. Across the same period of elements, the outermost electrons are attracted more strongly to the nucleus, thus reducing the atomic radius. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Ionic radius The ionic radius is the distance between the nucleus and the electron in the outermost shell of an ion. Group 1 Group 2 Group 13 Group 16 Group 17 Li+ Li Be2+ Be B3+ B O O2- F F- 90 134 59 90 41 82 73 126 71 119 Na+ Na Mg2+ Mg Al3+ Al S S2- Cl Cl- 116 154 86 130 68 118 102 170 99 167 K+ K Ca2+ Ca Ga3+ Ga Se Se2- Br Br- 152 196 114 174 76 126 116 184 114 182 Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Ionic radius Ionic radius increases when moving down the group and the explanation is similar to that of atomic radius. Ionic radius decreases when moving across the period for ions of the same type. For example,  Ionic radius Li+ > Be2+ > B3+  Ionic radius N3- > O2- > F- Ions with the same number of electrons and the same electron configuration are said to be isoelectronic.  Li+, Be2+, B3+ are isoelectronic. (i.e. 2)  N3-, O2-, F- are also isoelectronic. (i.e. 2.8) Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Ionic radius Cation is smaller than their neutral atom. Anion is bigger than their neutral atom. When an atom loses electrons to form a cation, the electrons are lost from the outermost shell; consequently, it loses the outermost electron shell and the other electrons are more strongly attracted to the nucleus, resulting in the cation smaller than its corresponding atom. When electrons are added to an atom forming an anion, the added electrons repels other electrons, resulting in the anion larger than its corresponding atom. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Activity 3 Explain why: a) Atomic radius of S < Atomic radius of Al S and Al are found in the same period. S has more protons and electrons than Al. The outermost electrons are in the same shell with relative similar shielding effect. The higher the number of protons attracts the outermost electrons more strongly to the nucleus, reducing the atomic radius Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Activity 3 Explain why: b) Ionic radius of S2- > Ionic radius of Al3+ S and Al are found in the same period. S2- has 2 electrons added in the outermost shell to form an anion. It has 3 electron shells. Al3+ has 3 electrons removed from the outermost shell to form cation, leaving it with 2 electron shells, S2- has one more electron shell. S2- has one more electron shell than Al3+, hence it has a larger ionic radius Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE 1st Ionisation energy (IE) The 1st ionisation energy is the energy required to completely remove one mole of the outermost electrons from one mole of gaseous atoms to produce one mole of gaseous ions (cations) with a charge of 1+. + −− −− − − − − − − − ++ ++ +++ + + ++ − −  − − ++ ++ +++ + + ++ − − + − + − e −− −− ov rem Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE 1st ionisation energy Ionisation energy trends Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Ionisation energy Across the same period, 1st ionisation energy of elements increases as it gets harder to remove an electron. This is the result of increasing positive nuclear charge across the same period without the addition of any extra electron shells to shield the outer electrons. The atomic radius gets smaller and the outermost electrons are attracted more strongly, hence, higher energy is required. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Ionisation energy Down the group, 1st ionisation energy of elements decreases as it gets easier to remove an electron. The outermost electron lies further from the nucleus with the addition of extra electron shells. There is an increase in shielding effect due to more inner electrons. The outmost electron experiences more repulsion from inner electrons, thus resulting in weaker attraction to the nucleus, hence less energy required to remove them. IE is decreasing down the group Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Electronegativity Electronegativity is a value that indicates the ability an atom to attract electrons to itself in a chemical bond. Atoms with high electronegativity will attract more electrons to itself. Atoms with low electronegativity will tend to lose their own electrons. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Electronegativity Electronegativity trends. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Electronegativity Electronegativity decreases down a group. Moving down the group, atoms increase in size, with a greater number of energy levels/shells. The extra energy levels and increased radius keep the bonding electrons further away from the nucleus. Thus, atoms further down groups have less attraction for the bonding electrons. Electronegativity increases across a period. Moving across the same period, atoms have a greater nuclear charge and a smaller covalent radius. This allows the nucleus to attract the bonding electrons more strongly. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Activity 4 Determine whether: a) S or Cl has a larger 1st ionisation energy S and Cl are in the same period however Cl has a higher nuclear charge than S which attracts the outermost electrons more strongly to the nucleus, making it harder to remove. Hence, Cl has a larger 1st ionisation energy than S. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Activity 4 Determine whether: b) Mg or Ca has a lower electronegativity value Mg and Ca are found in the same group. Ca has a lower electronegativity than Mg due to Ca having a larger atomic size which keeps the bonding electrons further away from the nucleus, hence decreasing the attraction for the bonding electrons. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Section 4 Group 2 elements and its compounds Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Group 2 elements Known as alkaline earth metals. Soft, silver metals that are harder and denser than Group 1 metals. Group 2 metals become more reactive going down the group. Group 2 metals form cations with a charge of +2 by losing 2 electrons. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Group 2 elements Group 2 metals are reducing agents as it form cations. (A reducing agent loses electrons to other substances in a redox reaction and gets oxidised to a higher oxidation state) Based on the Eϴ values: Element Equation Standard electrode potential (Eϴ / V) Beryllium Be2+ (aq) + 2e Be (s) -1.85 Magnesium Mg2+ (aq) + 2e Mg (s) -2.37 Calcium Ca2+ (aq) + 2e Ca (s) -2.87 Strontium Sr2+ (aq) + 2e Sr (s) -2.90 Barium Ba2+ (aq) + 2e Ba (s) -2.91 Barium has the highest tendency to be oxidised and hence is the strongest reducing agent. Beryllium is the weakest reducing agent. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Reaction of Group 2 elements Reaction with oxygen Group 2 elements react with oxygen to form metal oxides. Examples: 2Mg (s) + O2 (g) 2MgO (s) 2Ca (s) + O2 (g) 2CaO (s) Reaction with halogens Group 2 elements react with halogens to form metal halides. Examples: Mg (s) + Cl2 (g) MgCl2 (s) Ca (s) + Cl2 (g) CaCl2 (s) Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Reaction of Group 2 elements Reaction with steam Magnesium burns in steam with a bright white flame to produce magnesium oxide and hydrogen gas. Mg (s) + H2O (g) MgO (s) + H2 (g) Reaction with warm water Magnesium will also react with warm water, giving magnesium hydroxide and hydrogen gas. Mg (s) + 2H2O (l) Mg(OH)2 (s) + H2 (g) Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Reaction of magnesium with water https://www.youtube.com/watch?v=u_1uLP30uxY Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Reaction of Group 2 elements Reaction with cold water Other Group 2 elements (except beryllium and magnesium) react with cold water to form metal hydroxides and hydrogen gas. Example: Ca (s) + 2H2O (l) Ca(OH)2 (aq) + H2 (g) Group 2 hydroxides become more soluble down the group. The hydroxides produced make the water alkaline. Mg(OH)2 is classified as insoluble in water and Ca(OH)2 is considered reasonably soluble in water. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Reaction of calcium with water https://www.youtube.com/watch?v=i-rFsFwdkTU Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Group 2 carbonates Decomposition of carbonates Group 2 carbonates decompose on heating to produce group 2 oxides and carbon dioxide gas. MgCO3 (s) MgO (s) + CO2 (g) CaCO3 (s) CaO (s) + CO2 (g) Group 2 carbonates are more thermally stable as you go down the group. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Group 2 carbonates Decomposition of carbonates Metal ions are bigger going down Group 2 but has the same charge. This means the charge density (charge/volume) is reduced going down the group. The metal cation is able to polarise the carbonate anion as shown. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Group 2 carbonates Decomposition of carbonates A metal cation with a high charge density has strong polarising power. It can polarise the carbonate ion, making it more likely to split into CO2 and O2- when heated. A metal cation with a low charge density has weak polarising power, meaning the carbonate ion is less polarised, and therefore more thermally stable. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Group 2 carbonates Decomposition temperature Metal carbonates Decomposition temperature (oC) BeCO3 159 MgCO3 350 CaCO3 832 SrCO3 1340 BaCO3 1450 Group 2 carbonates are more thermally stable as you go down the group. (thus the temp increases) Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Activity 5 Element X, Y and Z are found in Group 2 of the periodic table with atomic number  20. The table below shows the observations made when X, Y and Z react with warm water. Identify element X, Y and Z. Element Reaction with water X A colourless solution is formed Y No reaction Z A solution with white precipitate (insoluble) is formed X: Calcium (Ca), since it recats with water to form Ca(OH)2 which dissolves in water Y: Beryllium (Be), since it does not react with water Z: Magnesium (Mg), since it reacts with warm water to form Mg(OH)2 which is insoluble in water and appears as a white ppt. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Activity 6 Magnesium nitrate, Mg(NO3)2 decomposes to magnesium oxide, nitrogen dioxide and oxygen when heated. a) Write down the chemical equation for this reaction. b) Predict whether Ca(NO3)2 has a higher or lower decomposition temperature than Mg(NO3)2. 2Mg(NO3)2 (s)  2MgO (s) + 4NO2 (g) + O2 (g) Ca(NO3)2 has a higher decomposition temperature since Ca has a lower charge density and weaker polarising power, meaning the nitrate ion is less polarised, and therefore more thermally stable Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Section 5 Group 17 elements and its compounds Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Group 17 elements Known as halogens. Exists as diatomic molecules: F2 (g), Cl2 (g), Br2 (l), I2 (s) Group 17 elements become less reactive going down the group. Group 17 elements form anions with a charge of -1 by gaining 1 electron. The physical state changes from gas, (F2 and Cl2), liquid (Br2) to solid (I2) down the Chlorine Bromine Iodine group. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Group 17 elements Melting and boiling point F2 (g), Cl2 (g), Br2 (l), I2 (s) are non-polar molecules. Weak Van der Waals forces exists between the molecules. As the molecules become larger they have more electrons that can move around to set up temporary dipoles. Stronger Van der Waals forces exist between the larger molecules. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Group 17 elements Melting and boiling point Halogen Melting point (oC) Boiling point (oC) F2 -220 -188 Cl2 -101 -35 Br2 -7.2 58.8 I2 114 184 The melting and boiling point of the halogens increases down the group. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Group 17 elements Group 17 elements are oxidising agents as it form anions. (An oxidising agent gains electrons from other substances in a redox reaction and gets reduced to a lower oxidation state) Based on the Eϴ values: Element Equation Standard electrode potential (Eϴ / V) Fluorine F2 (g) + 2e 2F- (aq) +2.87 Chlorine Cl2 (g) + 2e 2Cl- (aq) +1.36 Bromine Br2 (l) + 2e 2Br- (aq) +1.07 Iodine I2 (s) + 2e 2I- (aq) +0.54 Fluorine has the highest tendency to be reduced and hence is the strongest oxidising agent. Iodine is the weakest oxidising agent. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Reactions of Group 17 elements Displacement reaction A halogen that is a strong oxidising agent will displace a halogen that has a lower oxidising power from one of its compounds. Cl2 (aq) + 2KBr (aq) 2KCl (aq) + Br2 (aq) Cl2 (aq) + 2KI (aq) 2KCl (aq) + I2 (aq) Br2 (aq) + 2KI (aq) 2KBr (aq) + I2 (aq) Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Displacement reactions https://www.youtube.com/watch?v=HW2jRyQ3dzo Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Reactions of Group 17 elements Reaction with hydrogen Halogens react with hydrogen to form hydrogen halides. However, the reaction rate varies greatly for each halogen. Halogen Reaction Conditions Fluorine F2 (g) + H2 (g) 2HF (g) Combines explosively even in cold and dark Chlorine Cl2 (g) + H2 (g) 2HCl (g) Explodes if exposed to sunlight and a flame Bromine Br2 (g) + H2 (g) 2HBr (g) Combines with mild explosion under a flame Iodine I2 (g) + H2 (g) 2HI (g) Combines partially even with constant heating Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Reactions of Group 17 elements Reaction with water Halogens react with water to form halides and hypohalides. The halogen gases vary in their reactions with water due to their different electronegativities. Because fluorine (F2) is so electronegative, it can displace oxygen from water. The products of this reaction include oxygen gas and hydrogen fluoride. A hypohalite is an oxyanion containing a halogen is oxidation state 1+ Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Reactions of Group 17 elements Reaction with water Halogen Reaction Fluorine 2F2 (g) + 2H2O (l) 4HF (aq) + O2 (g) Chlorine Cl2 (g) + H2O (l) → HCl (aq) + HOCl (aq) Bromine Br2 (g) + H2O (l) → HBr (aq) + HOBr (aq) Iodine l2 (g) + H2O (l) → Hl (aq) + HOl (aq) Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Reactions of halide ions Reaction with silver nitrate (AgNO3) This reaction is used as a test to identify which halide ion is present. Halogen Reaction Observations Fluorine NA No precipitate Chlorine Ag+ (aq) + Cl- (aq) AgCl (s) White precipitate Bromine Ag+ (aq) + Br- (aq) AgBr (s) Cream precipitate Iodine Ag+ (aq) + I- (aq) AgI (s) Pale yellow precipitate Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Reactions of halide ions Reaction of silver halide precipitates with ammonia The silver halide precipitates can be treated with ammonia solution to help differentiate between them. Precipitate Reaction Observations AgCl (s) AgCl (s) + 2NH3 (aq) [Ag(NH3)2]+ Silver chloride dissolves in (aq) + Cl (aq) - dilute ammonia to form a colourless complex ion AgBr (s) AgBr (s) + 2NH3 (aq) [Ag(NH3)2]+ Silver bromide dissolves in (aq) + Br (aq) - concentrated ammonia to form a colourless complex ion AgI (s) No reaction Silver iodide does not react with ammonia – it is too insoluble. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Halide ion tests https://www.youtube.com/watch?v=ALNzlPHGh9I Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Hydrogen halides HF and HCl are very stable to heat. They don't split up into hydrogen and fluorine or chlorine again if heated to any normal lab temperature. HBr splits slightly into hydrogen and bromine on heating, and HI splits to an even greater extent. The reason for this lies in the strengths of the hydrogen-halogen bonds. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Hydrogen halides Down the group, the strength of the hydrogen- halogen bonds become weaker. Bond Bond energy (kJ/mol) H-F +562 H-Cl +431 H-Br +366 H-I +299 Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Hydrogen halides Down the group, the halogen atoms are getting bigger and the bond length is longer. The bonding pair of electrons is getting further from the halogen nucleus which means weaker bond. The weaker the bond, the less heat energy you need to supply to break it. Hence, Group 17 halides are less thermally stable as you go down the group. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Activity 7 Halogen X undergoes the reaction as shown in the table below. Identify halogen X. Reactant Reaction KCl NA KBr X2 + 2KBr 2KX + Br2 KI X2 + 2KI 2KX + I2 X is Chlorine. Since halogen X undergoes reaction with KBr and KI, it must be more reactive halogen than Br2 and I2. Since there is no reaction with KCl, X must be Cl. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Activity 8 In your team, summarize the properties and reactions of the elements and compounds in Group 2 and Group 17 in a mindmap as shown below. Trends in periodic table - Across period - Down the group Properties of Group 2 Properties of Group 17 elements Periodic Table elements Reactions of Group 2 Reactions of Group 17 elements and elements and compounds compounds Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE IT’S TIME FOR 1. Go to “https://kahoot.it/” on your laptop or mobile phone. 2. Enter Game PIN generated by your lecturer. 3. Choose your Nickname and Get Ready!  OFFICIAL (CLOSED) \ NON- SENSITIVE Learning outcomes Identify variation in the electron configurations down a Group and across a Period. Describe and explain qualitatively the general trends and variations in atomic radius, ionic radius, first ionisation energy and electronegativity down a Group and across a Period. Describe and explain the trend in volatility of the Group 17 elements. Describe and deduce from E⦵ values the relative reactivity of elements of (i) Group 2 as reducing agents, (ii) Group 17 as oxidising agents. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Learning outcomes Describe and explain the trend in thermal stability of (i) Group 2 carbonates in terms of the charge density of the cation and the polarisability of the large anion, (ii) Group 17 hydrides in terms of bond energies. Predict the characteristic properties of an element in a given Group by using knowledge of chemical periodicity. Deduce the nature, possible position in the Periodic Table, and identity of unknown elements from given information of physical and chemical properties. Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE Further reading 1. Periodic Trends - Chemistry LibreTexts 2. https://www.chemguide.co.uk/inorganic/group2me nu.html 3. https://www.chemguide.co.uk/inorganic/group7me nu.html 4. The Thermal Stability of the Nitrates and Carbonat es - Chemistry LibreTexts Copyright 2024 © Republic Polytechnic, Singapore  OFFICIAL (CLOSED) \ NON- SENSITIVE smaller atomic radius  higher charge density if metal ion  higher polarizing power of the metal ion  easier to break apart NO3- ion  lower decomposition temp Copyright 2024 © Republic Polytechnic, Singapore