WEBVTT 00:00:00.500 --> 00:00:03.976 Welcome to GCSE Edexcel Science revision. 00:00:04.126 --> 00:00:07.755 Unit S C 17: Groups in the periodic table. 00:00:10.433 --> 00:00:14.658 Group 1 alkali metals include lithium, sodium and potassium. 00:00:14.808 --> 00:00:19.745 They have one outer-shell electron and commonly form plus 1 ions by losing it. 00:00:22.400 --> 00:00:30.537 They are soft metals, can be cut with a knife in a controlled demonstration, and have relatively low melting points compared with most metals. 00:00:30.687 --> 00:00:32.617 They conduct electricity. 00:00:35.300 --> 00:00:40.856 They react readily with non-metals such as oxygen, forming oxygen-containing compounds. 00:00:41.006 --> 00:00:45.464 Fresh surfaces tarnish in air, so samples are commonly stored under oil. 00:00:48.133 --> 00:00:57.306 With water they form a metal hydroxide and hydrogen, making an alkaline solution: metal plus water produces metal hydroxide plus hydrogen. 00:00:59.967 --> 00:01:03.405 Lithium floats, moves and fizzes relatively gently. 00:01:03.555 --> 00:01:08.505 Sodium reacts more vigorously, often melts into a ball and moves across the water. 00:01:08.655 --> 00:01:13.083 Potassium reacts still more vigorously and can ignite with a lilac flame. 00:01:15.733 --> 00:01:18.016 These water reactions release heat. 00:01:18.166 --> 00:01:26.835 Sodium and potassium can melt because heat exceeds their relatively low melting temperatures; lithium does not normally melt in the same demonstration. 00:01:29.500 --> 00:01:35.973 The balanced sodium equation is 2 N A plus 2 H 2 O produces 2 N A O H plus H 2. 00:01:36.123 --> 00:01:41.190 Hydroxide ions in the solution explain why an indicator shows alkalinity. 00:01:41.340 --> 00:01:45.365 The reaction is exothermic and increasingly vigorous down group 1. 00:01:50.033 --> 00:01:55.217 Alkali-metal demonstrations require teacher control, shielding and small samples. 00:01:55.367 --> 00:01:59.756 Do not attempt them at home or assume oil storage makes the metal harmless. 00:02:02.433 --> 00:02:06.830 Reactivity increases down group 1: lithium < sodium < potassium. 00:02:06.980 --> 00:02:11.684 Predict rubidium and caesium to be more reactive than potassium, using the trend. 00:02:14.367 --> 00:02:17.551 Down group 1, atoms have more electron shells. 00:02:17.701 --> 00:02:20.579 The outer electron is further from the nucleus. 00:02:20.729 --> 00:02:25.199 Inner electrons reduce the nucleus’s attraction to it: this is shielding. 00:02:27.867 --> 00:02:34.286 Although nuclear charge increases, distance and shielding reduce the effective attraction to the outer electron. 00:02:34.436 --> 00:02:37.757 It is lost more readily, making the metal more reactive. 00:02:37.907 --> 00:02:40.786 Group 1 reacts by electron loss, not gain. 00:02:45.467 --> 00:02:50.474 Lithium is two, one; sodium two, eight, one; potassium two, eight, eight, one. 00:02:50.624 --> 00:02:56.928 The same outer count gives similar reactions; the growing shell count helps explain changing reactivity. 00:02:57.078 --> 00:03:01.772 One outer electron remains; added inner shells increase distance and shielding. 00:03:06.433 --> 00:03:12.307 Forming a plus 1 ion is oxidation: M produces M, charge plus, plus an electron. 00:03:12.457 --> 00:03:19.793 Do not explain the trend by saying group 1 atoms gain electrons or that more protons alone must increase attraction. 00:03:22.467 --> 00:03:28.397 Atomic number rises down the group, but atomic number by itself is not a complete explanation. 00:03:28.547 --> 00:03:32.184 Connect shell count, shielding, attraction and electron loss. 00:03:34.867 --> 00:03:41.937 Group 7 halogens have seven outer-shell electrons and commonly gain one electron to form minus 1 halide ions. 00:03:42.087 --> 00:03:43.709 They are non-metals. 00:03:43.859 --> 00:03:50.031 Their molecules contain two atoms (they are diatomic), for example C L 2, B R 2 and I 2. 00:03:52.700 --> 00:03:59.397 At room temperature chlorine is a pale green gas, bromine a red-brown liquid and iodine a grey-black solid. 00:03:59.547 --> 00:04:04.185 Iodine vapour is purple; do not confuse vapour colour with the bulk solid. 00:04:06.867 --> 00:04:12.721 From chlorine to bromine to iodine, melting point, boiling point and density generally increase. 00:04:12.871 --> 00:04:18.493 Stronger intermolecular attractions between larger molecules explain the boiling-point trend. 00:04:21.167 --> 00:04:29.505 Approximate source-table values are chlorine melting minus 101 degrees Celsius and boiling minus 34 degrees Celsius; 00:04:29.655 --> 00:04:33.814 bromine minus 7 degrees Celsius and 59 degrees Celsius; 00:04:33.964 --> 00:04:39.743 iodine 114 degrees Celsius and 184 degrees Celsius. 00:04:39.893 --> 00:04:42.496 Use supplied values for state predictions. 00:04:42.646 --> 00:04:47.391 At about 20 degrees Celsius, compare temperature with melting and boiling points. 00:04:52.067 --> 00:04:58.519 Halogens react with metals to form metal halides: 2 N A plus C L 2 produces 2 N A C L. 00:04:58.669 --> 00:05:05.452 Sodium chloride is table salt; fluoride compounds are used in toothpaste, rather than elemental fluorine. 00:05:08.133 --> 00:05:11.777 Hydrogen reacts with halogens to form hydrogen halides. 00:05:11.927 --> 00:05:19.979 Dissolving hydrogen chloride in water gives hydrochloric acid; hydrogen chloride gas and the aqueous acid are different conditions. 00:05:22.633 --> 00:05:27.444 Chlorine bleaches damp blue litmus paper, often after it first turns red. 00:05:27.594 --> 00:05:33.885 Chlorine can kill microorganisms and remove colour, but harmful gas must be handled with proper controls. 00:05:36.567 --> 00:05:41.547 Halogen reactivity decreases down the group: fluorine > chlorine > bromine > iodine. 00:05:41.697 --> 00:05:45.672 Predict astatine to be less reactive than iodine from this pattern. 00:05:48.333 --> 00:05:54.541 Down the group, extra shells increase distance and shielding, weakening the attraction for an incoming electron. 00:05:54.691 --> 00:05:57.293 The atom gains an electron less readily. 00:05:57.443 --> 00:06:02.137 Halogens react by gaining electrons; the trend is opposite to group 1. 00:06:06.800 --> 00:06:12.005 A more reactive halogen displaces a less reactive halogen from a halide solution. 00:06:12.155 --> 00:06:18.851 Chlorine displaces bromine from bromide and iodine from iodide; bromine displaces iodine from iodide. 00:06:19.001 --> 00:06:24.505 Chloride is not displaced by bromine or iodine; a halogen cannot displace itself. 00:06:29.167 --> 00:06:38.466 Chlorine plus sodium bromide produces sodium chloride plus bromine: C L 2 plus 2 N A B R produces 2 N A C L plus B R 2. 00:06:38.616 --> 00:06:46.148 Ionic equation: C L 2 plus 2 B R, charge minus, produces 2 C L, charge minus, plus B R 2. 00:06:48.800 --> 00:06:55.707 Chlorine gains electrons and is reduced: C L 2 plus 2 electrons produces 2 C L, charge minus,. 00:06:55.857 --> 00:07:03.287 Bromide ions lose electrons and are oxidised: 2 B R, charge minus, produces B R 2 plus 2 electrons. 00:07:03.437 --> 00:07:05.463 The displacement is redox. 00:07:05.613 --> 00:07:09.377 Chlorine is reduced; bromide, not chlorine, is oxidised. 00:07:14.033 --> 00:07:18.409 Iodine cannot displace chlorine from chloride or bromine from bromide. 00:07:18.559 --> 00:07:22.697 Equal-halogen combinations do not produce a displacement reaction. 00:07:25.367 --> 00:07:31.243 Use small controlled volumes and observe solution colour changes; compare with reference solutions. 00:07:31.393 --> 00:07:36.694 Colours depend on solvent and concentration, so use the given practical information. 00:07:39.367 --> 00:07:43.555 Group 0 noble gases include helium, neon, argon and krypton. 00:07:43.705 --> 00:07:47.722 At room temperature they are colourless gases with low boiling points. 00:07:47.872 --> 00:07:51.321 Each particle is a single atom: they are monatomic. 00:07:54.000 --> 00:08:01.699 Their atoms have complete outer shells: helium has two electrons in its first shell, while neon and argon have eight in their outer shells. 00:08:01.849 --> 00:08:06.193 A full first shell contains two; helium does not need eight electrons. 00:08:10.867 --> 00:08:18.203 Full shells explain their very low reactivity compared with other groups and why they do not commonly form ions or compounds. 00:08:18.353 --> 00:08:24.165 Some heavier noble gases can form compounds under special conditions, so avoid “never react”. 00:08:26.833 --> 00:08:31.697 Boiling point and density generally increase down the familiar noble-gas group. 00:08:31.847 --> 00:08:38.033 Larger atoms have stronger intermolecular attractions, requiring more energy to separate them on boiling. 00:08:40.700 --> 00:08:42.876 Noble gases are non-flammable. 00:08:43.026 --> 00:08:51.014 Their low reactivity and occurrence as uncombined atoms made their discovery difficult; several were identified in the late nineteenth century. 00:08:53.667 --> 00:09:00.631 Helium's low density and non-flammability make it suitable for balloons and airships; hydrogen is light but flammable. 00:09:03.300 --> 00:09:11.426 Argon provides an unreactive atmosphere for welding and other oxidation-sensitive processes, including protective gas applications. 00:09:11.576 --> 00:09:18.261 Neon emits red-orange light in electrical discharge tubes; krypton is used in some photographic flash lamps. 00:09:18.411 --> 00:09:22.828 Match the application to the property, rather than simply memorising names. 00:09:27.500 --> 00:09:34.827 Although ordinary noble gas samples conduct poorly, an electrical discharge can excite or ionise gas and produce light. 00:09:34.977 --> 00:09:38.809 Do not equate a glowing sign with normal metal-like conduction. 00:09:41.467 --> 00:09:44.069 That completes Groups in the periodic table. 00:09:44.219 --> 00:09:47.565 Revisit the notes and test yourself on the revision website.