2017 ©Pearson part. in or whole Jim Clark, Steve Owen, Rachel Yu Rachel Owen, Jim Clark, Steve Student Book CHEMISTRY GCSE(9 INTERNATIONAL EDEXCEL in included eBook distribution or circulation resale, for Not discretion. publisher at change to subject content all –1) proof, Uncorrected 2017 ©Pearson part. in or Student Book CHEMISTRY GCSE(9 INTERNATIONAL EDEXCEL whole Rachel Yu Rachel Steve Owen Jim Clark in distribution or circulation resale, for Not discretion. publisher at change to subject content all –1) proof, Uncorrected CONTENTS 2017 ©Pearson part. in or INDEX GLOSSARY APPENDICES CHEMISTRY ORGANIC UNIT 4: ENERGETICS UNIT 3: CHEMISTRY INORGANIC UNIT 2: PRINCIPLESOFCHEMISTRY UNIT 1: INTRODUCTION whole in distribution or circulation resale, for Not discretion. publisher at change to subject content all proof, 334 327 319 254 206 140 Uncorrected 02 VI v 2017 ©Pearson part. in or in trains thatlevitate abovethetracks. in trains used thatare superconductors development ofthesenewmaterials, forinstancehigh-temperature involvedinthe chemistsare Inorganic properties. fornewmaterials withexciting searching always scientistsare of themostimportant materials thatweuseineveryday life.However, some metalsandtheseare are Table and theircompounds.MostoftheelementsinPeriodic chemistsasaguideto understandingthebehaviourofelements principle usedbyinorganic unifying Table isthegreat Periodic andtheyformahugevarietyofcompounds.The different very oftheseelementsare compoundsformedbycarbon.Theproperties organic form, except andthecompoundsthey Table chemistryInorganic isthestudyofall theelementsinPeriodic INORGANIC CHEMISTRY INORGANIC UNIT 2 ▲ EXTRACTION AND USES OF METALS 183 AND USESOFMETALS EXTRACTION 141 ALKALI METALS THE whole ACIDS, BASES AND SALT PREPARATIONS 198 PREPARATIONS AND SALT BASES ACIDS, Figure 11.1 The maglev train levitates above the track due to superconducting materials. dueto superconducting levitates abovethetrack 11.1Themaglevtrain Figure in distribution or THE HALOGENS149 circulation resale, for Not ACIDS, ALKALIS AND TITRATIONS 191 ALKALISANDTITRATIONS ACIDS, GASES IN THE ATMOSPHERE GASES 157 IN THEATMOSPHERE discretion. publisher at change to subject REACTIVITY SERIES166 REACTIVITY content all proof, Uncorrected INORGANIC CHEMISTRY THE ALKALI METALS 123 2017 11 THE ALKALI METALS ©Pearson We have already looked at the Periodic Table in Chapter 4. Here we will look at the properties of the elements in Group 1 part. of the Periodic Table: the alkali metals. in or whole in ▶ Figure 11.2 Potassium reacting with water. The alkali metals are all distribution reactive metals that react vigorously with water. or LEARNING OBJECTIVES circulation ◼ Understand how the similarities in the reactions of ◼ Use knowledge of trends in Group 1 to predict the these elements with water provide evidence for their properties of other alkali metals. resale, recognition as a family of elements. for CHEMISTRY ONLY ◼ Understand how the differences between the reactions ◼ Explain the trend in reactivity in Group 1 in terms of Not of these elements with air and water provide evidence electronic configurations. for the trend in reactivity in Group 1. discretion. The elements in Group 1 of the Periodic Table are called the alkali metals. The Li lithium group contains the elements shown in Figure 11.3. Francium (pronounced france-ee-um), at the bottom of the group, is radioactive. publisher sodium Na One of its isotopes is produced during the radioactive decay of uranium-235, at but is extremely short-lived. At any one time scientists estimate that there is K potassium only about 20–30 g of francium present in the whole of the Earth’s crust and no one has ever seen a piece of francium. When you know about the rest of Group 1 change to Rb rubidium you can predict what francium would be like. We will make those predictions later. Cs caesium subject PHYSICAL PROPERTIES francium Fr Melting point/°C Boiling point/°C Density/g/cm3 content all ▲ Figure 11.3 The alkali metals. Li 181 1342 0.53 proof, Na 98 883 0.97 K 63 760 0.86 Rb 39 686 1.53 Uncorrected Cs 29 669 1.88 124 INORGANIC CHEMISTRY THE ALKALI METALS The melting and boiling points of the elements are very low for metals, and get 2017 lower as you move down the group. The reason that the melting points decrease is that the atoms get bigger as we go down the group. In the metallic lattice, the nuclei of the positive ions are ©Pearson further from the delocalised electrons in caesium and therefore there is weaker electrostatic attraction. part. Their densities tend to increase down the group, although not regularly. Lithium, in sodium and potassium are all less dense than water, and so will float on it. or The metals are also very soft and are easily cut with a knife, becoming softer as you move down the group. They are shiny and silver when freshly cut, but whole tarnish very quickly on exposure to air. in STORAGE AND HANDLING All these metals are extremely reactive and get more reactive as you go distribution down the group. They all react quickly with oxygen in the air to form oxides, or and react rapidly with water to form strongly alkaline solutions of the metal hydroxides. This is why the Group 1 metals are commonly known as the alkali metals. circulation To stop them reacting with oxygen or water vapour in the air, lithium, sodium and potassium are stored under oil. Rubidium and caesium are so reactive that they have to be stored in sealed glass tubes to stop any possibility of oxygen resale, getting at them. for Great care must be taken not to touch any of these metals with bare fingers. ▲ Figure 11.4 Lithium, sodium and potassium Not There could be enough sweat on your skin to give a reaction, producing lots of have to be kept in oil to stop them reacting with heat and a very corrosive metal hydroxide. oxygen in the air. A FAMILY OF ELEMENTS discretion. There are two reasons that we put these elements in Group 1: 1 They all have one electron in their outer shell (energy level). The electronic configurations are: publisher DID YOU KNOW? at lithium 2, 1 Historically alkali metals were sodium 2, 8, 1 put in the same group because potassium 2, 8, 8, 1 change of similarities in properties, to 2 They have similar chemical properties, for instance: before anyone knew anything ◾◾ they all react with water (this will be discussed below) in the same way to about electrons! form a hydroxide with the formula MOH (LiOH, NaOH etc.) and hydrogen subject ◾◾ they react with oxygen to form an oxide with the formula M2O (Na2O, K2O KEY POINT etc.) content ‘M’ simply represents any one of the ◾◾ they react with halogens to form compounds with the formula MX (LiCl, all alkali metals. ‘X’ represents any one of KBr etc.) the halogens. ◾◾ they form ionic compounds which contain an M+ ion (Na+, K+ etc.). proof, REMINDER The chemical properties depend on the number of electrons in the outer shell You might need to remind yourself (energy level). The Group 1 elements react in very similar ways because they why the formula is MOH by looking all have the same number of electrons in the outer shell (one), so reason 2 is at Chapter 7. The charge on the really just a consequence of reason 1. Uncorrected hydroxide ion is 1–. We will discuss the chemical properties in more detail below. INORGANIC CHEMISTRY THE ALKALI METALS 125 2017 THE REACTIONS WITH WATER GROUP 1: THE ALKALI METALS All these metals react in the same way with water to produce a metal ©Pearson hydroxide and hydrogen: alkali metal + water alkali metal hydroxide + hydrogen part. → in 2M + 2H2O → 2MOH + H2 or The main difference between the reactions is how quickly they happen. whole As you go down the group, the metals become more reactive and the in reactions occur more rapidly. The reaction between sodium and water is typical. distribution WITH SODIUM or HINT 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g) Strictly speaking, most of the time sodium floats and the sodium is reacting it is present hydrogen melts into a ball as molten sodium, not solid sodium. evolved circulation Writing (l) for the state symbol has the hydrogen evolved potential to confuse an examiner and is probably best avoided! ball moves rapidly resale, around the surface for Not HINT discretion. When you are asked about this in the exam, you are often asked to compare white trail formed which water the reactions of sodium and lithium so dissolves in the water you should explain how you can see it Figure 11.5 Sodium reacting with water. The white trail is the sodium hydroxide, which dissolves publisher is slower. So, for example, you can say ▲ in water to form a strongly alkaline solution. at that it fizzes more slowly, or the lithium moves around more slowly, or takes longer to disappear. The main observations you can make when this reaction occurs are: change ◾◾ The sodium floats because it is less dense than water. HINT to When asked to write observations in ◾◾ The sodium melts into a ball because its melting point is low and a lot of the exam it is better to write ‘fizzing/ heat is produced by the reaction. subject bubbling/effervescing’ rather than ‘a ◾◾ There is fizzing because hydrogen gas is produced. gas is given off’ because the fizzing/ bubbling/effervescing is what you ◾◾ The sodium moves around on the surface of the water. Because the actually see. content hydrogen isn’t given off symmetrically around the ball, the sodium is pushed around the surface of the water, like a hovercraft. all ◾◾ The piece of sodium gets smaller and eventually disappears. The sodium is proof, used up in the reaction. ◾◾ If you test the solution that is formed with universal indicator solution, you will see that the universal indicator goes blue, indicating an alkaline solution has been formed. The metal hydroxide is alkaline (the solution contains the OH− ion).