The Facts The reactions with oxygen Formation of simple oxides The excess energy evolved makes the overall process exothermic. In all the other cases in Group 1, the overall reaction would be endothermic. The Group II elements are powerful reducing agents. Why do these metals form nitrides on heating in air? All group 2 elements except barium react directly with oxygen to form the simple oxide MO. It can't be done! There is an increase in the tendency to form the peroxide as you go down the Group. All of these processes absorb energy. Now imagine bringing a small 2+ ion close to the peroxide ion. Reaction with halogens. The group 2 metals (M (s)) react with oxygen gas (O 2(g)) at room temperature and pressure to form oxides with the general formula MO as shown in the balanced chemical reactions below: 2Be (s) O 2(g) An example reaction is shown below: In this reaction, the is oxidised from 0 to +2. The chemical properties of Group2 elements are dominated by the strong reducing power of the metals. This energy is known as lattice energy or lattice enthalpy. Have questions or comments? On the whole, the metals burn in oxygen to form a simple metal oxide. The speed is controlled by factors like the presence of surface coatings on the metal and the size of the activation energy. In the whole of Group 2, the attractions between the 2+ metal ions and the 3- nitride ions are big enough to produce very high lattice energies. Lithium has by far the smallest ion in the Group, and so lithium nitride has the largest lattice energy of any possible Group 1 nitride. Reactions with water . The group 2 elements react vigorously with oxygen in a redox reaction, forming an oxide with the general formula where is the group 2 element. You will notice that the trend in the pH of the solutions formed goes from alkaline to acidic. What the metals look like when they burn is a bit problematical! You might possibly be able to imagine a trace of very pale greenish colour surrounding the white flame in the third video, but to my eye, they all count as a white flame. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. The strontium equation would look just the same. The lattice energy is greatest if the ions are small and highly charged - the ions will be close together with very strong attractions. Those reactions don't happen, and the nitrides of sodium and the rest are not formed. Why do some metals form peroxides on heating in oxygen? Calcium is quite reluctant to start burning, but then bursts dramatically into flame, burning with an intense white flame with a tinge of red at the end. However, in a reaction with steam it forms magnesium oxide and hydrogen. Exposed to air, it will absorb water vapour from the air, forming a solution. Now imagine bringing a small 2+ ion close to the peroxide ion. At room temperature, oxygen reacts with the surface of the metal. Reactions with dilute hydrochloric acid All the metals react with dilute hydrochloric acid to give bubbles of hydrogen and a colourless solution of the metal chloride. Nitrogen is often thought of as being fairly unreactive, and yet all these metals combine with it to produce nitrides, X3N2, containing X2+ and N3- ions. While it would be tempting to say that the reactions get more vigorous as you go down the Group, but it is not true. It is almost impossible to find any trend in the way the metals react with oxygen. Question: (a) Write Chemical Equations For The Reactions Of Oxygen With Group 1 Metals And Group 2 Metals Respectiv (4 Marks) (b) Discuss The Trend Of Thermal Stability Of Group 1 And Group 2 Peroxides. (a) describe the redox reactions of the Group 2 elements Mg to Ba: (i) with oxygen, (ii) with water; (b) explain the trend in reactivity of Group 2 elements down the group due to the increasing ease of forming cations, in terms of atomic size, shielding and nuclear attraction; Reactions of Group 2 compounds Barium: I have also only seen this burn on video, and although the accompanying description talked about a pale green flame, the flame appeared to be white with some pale green tinges. Electrons in the peroxide ion will be strongly attracted towards the positive ion. Why do some metals form peroxides on heating in oxygen? Reactions with oxygen. This page looks at the reactions of the Group 2 elements - beryllium, magnesium, calcium, strontium and barium - with air or oxygen. . To find the trend of reactions of metals with oxygen is almost impossible. This works best if the positive ion is small and highly charged - if it has a high charge density. Mg ribbon will often have a thin layer of magnesium oxide on it formed by reaction with oxygen. Water: Beryllium is reluctant to burn unless it is in the form of dust or powder. The has been reduced from 0 to -2. It explains why it is difficult to observe many tidy patterns. We say that the positive ion polarizes the negative ion. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. M = Mg, Ca, Sr,Ba --> I will be using 'M' as the general symbol for a Group II element in this topic. This is then well on the way to forming a simple oxide ion if the right-hand oxygen atom (as drawn below) breaks off. Energy is evolved when the ions come together to produce the crystal lattice. (b) Relative Reactivities of the Group 2 elements Mg → Ba shown by their redox reactions with: (i) Oxygen (ii) Water (iii) Dilute acids {Reactions with acids will be limited to those producing a salt and Hydrogen.} Mixtures of barium oxide and barium peroxide will be produced. questions on the reactions of Group 2 elements with air or oxygen, © Jim Clark 2002 (last modified February 2015), reactions of these metals with water (or steam). All Group 2 elements tarnish in air to form a coating of the metal oxide. As you go down the Group and the positive ions get bigger, they don't have so much effect on the peroxide ion. It would be tempting to say that the reactions get more vigorous as you go down the Group, but it isn't true. The strontium equation would look just the same. There are also problems with surface coatings. This is then well on the way to forming a simple oxide ion if the right-hand oxygen atom (as drawn below) breaks off. There are no simple patterns in the way the metals burn. 1.3.2 (a) Redox Reactions of Group 2 Metals. Beryllium has a very strong (but very thin) layer of beryllium oxide on its surface, and this prevents any new oxygen getting at the underlying beryllium to react with it. Ions of the metals at the top of the Group have such a high charge density (because they are so small) that any peroxide ion near them falls to pieces to give an oxide and oxygen. REACTIONS OF THE GROUP 2 ELEMENTS WITH AIR OR OXYGEN This page looks at the reactions of the Group 2 elements - beryllium, magnesium, calcium, strontium and barium - with air or oxygen. When the crystal lattices form, so much energy is released that it more than compensates for the energy needed to produce the various ions in the first place. Reaction with water Most Group II oxides react with water to produce the hydroxide e.g. Acid-Base reactions are not Redox reactions because there are no changes in Oxidation number. There are no simple patterns. Beryllium is reluctant to burn unless it is in the form of dust or powder. This energy has to be recovered from somewhere to give an overall exothermic reaction - if the energy can't be recovered, the overall change will be endothermic and won't happen. A reducing agent is the compound that gets oxidised in the reaction and, therefore, loses electrons. Once started, the reactions with Oxygen and Chlorine are vigorous: 2Mg(s) + O 2 (g) è2MgO(s) Ca(s) + Cl 2 (g) è CaCl 2 (s) All the metals except Beryllium form oxides in air at room temperature which dulls the surface of the metal. The Reactions with Air. It reacts with cold water to produce an alkaline solution of calcium hydroxide and hydrogen gas is released. Nitrogen is fairly unreactive because of the very large amount of energy needed to break the triple bond joining the two atoms in the nitrogen molecule, N2. CaO(s) + H2O(l) ——> Ca(OH)2(s) Hydroxides • basic strength also increases down group • this is because the solubility increases • the metal ions get larger so charge density decreases • there is a lower attraction between the OH¯ ions and larger dipositive ions Lithium is the only metal in Group 1 to form a nitride. We say that the positive ion polarises the negative ion. Ions of the metals at the top of the Group have such a high charge density (because they are so small) that any peroxide ion near them falls to pieces to give an oxide and oxygen. There is an increase in the tendency to form the peroxide as you go down the Group. REACTIONS OF THE GROUP 2 ELEMENTS WITH AIR OR OXYGEN. But how reactive a metal seems to be depends on how fast the reaction happens (i.e., Kinetics) - not the overall amount of heat evolved (i.e., Thermodynamics). Reactions with oxygen … All of these processes absorb energy. Reactivity increases down the group. 2Mg + O2 2MgO This needs to be cleaned off by emery paper before doing reactions with Mg ribbon. The activation energy is much higher. The equations for the reactions: As I said earlier, they are powerful reducing age… You haven't had to heat them by the same amount to get the reactions happening. You could argue that the activation energy will fall as you go down the Group and that will make the reaction go faster. Group 2 have 2 outer electrons which are less easily lost compared to group 1 At the top of group 2 ionisation energies are often too high for the electrons to be removed so they're relatively unreactive, reactivity increases down group 2 also. The general formula for this reaction is MO (where M is the group 2 element). Strontium and barium will also react with oxygen to form strontium or barium peroxide. The reactions of the Group 2 elements proceed more readily as the energy needed to form positive ions falls. This forms a white oxide, which covers the surface. For example, the familiar white ash you get when you burn magnesium ribbon in air is a mixture of magnesium oxide and magnesium nitride. The group 2 metals will burn in oxygen. e.g. You could argue that the activation energy will fall as you go down the Group and that will make the reaction go faster. Atomic and physical properties . Beryllium is reluctant to burn unless in the form of powder or dust. (i) The Reactions of Group 2 Elements with Oxygen. When something like magnesium nitride forms, you have to supply all the energy needed to form the magnesium ions as well as breaking the nitrogen-nitrogen bonds and then forming N3- ions. The activation energy will fall because the ionization energies of the metals fall. The activation energy will fall because the ionisation energies of the metals fall. Beryllium, magnesium and calcium don't form peroxides when heated in oxygen, but strontium and barium do. (3 Marks) (d) Heating Group 2 Carbonates, Such As CaCO3 Leads To Decomposition. with $$X$$ representing any group 2 metal. Group 2 reactions Reactivity of group 2 metals increases down the group Mg will also react slowly with oxygen without a flame. 2Mg + O2 2MgO This needs to be cleaned off by emery paper before doing reactions with Mg ribbon. All group 2 elements want to lose 2 electrons and all group 6 elements (oxygen) want to gain 2 electrons. Their ions only carry one positive charge, and so the lattice energies of their nitrides will be much less. This is in contrast to what happens in Group 1 of the Periodic Table (lithium, sodium, potassium, rubidium and caesium). Lithium is the only metal in Group 1 to form a nitride. strontium and water reaction. In this video I take a look at some of the different ways in which group 2 elements can react. The size of the lattice energy depends on the attractions between the ions. Further along though, a strong S-O bond keeps this together and more H+ is generated. The speed is controlled by factors like the presence of surface coatings on the metal and the size of the activation energy. 2.11 Group II elements and their compounds. My best guess would be the same sort of silvery sparkles that magnesium or aluminium powder burn with if they are scattered into a flame - but I don't know that for sure. When the crystal lattices form, so much energy is released that it more than compensates for the energy needed to produce the various ions in the first place. . The overall amount of heat evolved when one mole of oxide is produced from the metal and oxygen also shows no simple pattern: If anything, there is a slight tendency for the amount of heat evolved to decrease as you go down the Group. To be able to make any sensible comparison, you would have to have pieces of metal which were all equally free of oxide coating, with exactly the same surface area and shape, exactly the same flow of oxygen around them, and heated to exactly the same extent to get them started. To be able to make any sensible comparison, you would have to have pieces of metal which were all equally free of oxide coating, with exactly the same surface area and shape, exactly the same flow of oxygen around them, and heated to exactly the same extent to get them started. Electrons in the peroxide ion will be strongly attracted towards the positive ion. Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. This page looks at the reactions of the Group 2 elements - beryllium, magnesium, calcium, strontium and barium - with air or oxygen. Reactions. This is because the less electronegative sodium has a weak Na-O bond and the oxygen is more easily given up to react with H+. This energy has to be recovered from somewhere to give an overall exothermic reaction - if the energy can't be recovered, the overall change will be endothermic and will not happen. Only in lithium's case is enough energy released to compensate for the energy needed to ionise the metal and the nitrogen - and so produce an exothermic reaction overall. Beryllium: I can't find a reference anywhere (text books or internet) to the colour of the flame that beryllium burns with. The group 1 elements react with oxygen from the air to make metal oxides. If this is the first set of questions you have done, please read the introductory page before you start. They react violently in pure oxygen producing a white ionic oxide. A high charge density simply means that you have a lot of charge packed into a small volume. Describe the trend in the reactivity of group 2 elements with chlorine as you descend down the group. Strontium: I have only seen this burn on video. Legal. Energy is evolved when the ions come together to produce the crystal lattice (lattice energy or enthalpy). Reaction of Group-2 Metals with Cl 2 : All Gr-2 metals except Be react with chlorine to give ionic chlorides whereas Be reacts with chlorine to give covalent chloride . The reactions of the Group 2 metals with air rather than oxygen is complicated by the fact that they all react with nitrogen to produce nitrides. 2M(s) + O CCEA Chemistry. The Facts. Strontium forms this if it is heated in oxygen under high pressures, but barium forms barium peroxide just on normal heating in oxygen. . The peroxide ion, O22- looks like this: The covalent bond between the two oxygen atoms is relatively weak. Lithium has by far the smallest ion in the Group, and so lithium nitride has the largest lattice energy of any possible Group 1 nitride. Mg(s) + H2O(g) → MgO(s) + H2(g) b) Calcium is more reactive. It would be quite untrue to say that they burn more vigorously as you go down the Group. $Ba_{(s)} + O_{2(s)} \rightarrow BaO_{2(s)}$. It is easier for group 2 elements to lose 2 electrons the further away the electrons are from the nucleus ( as you go down there are more shells), hence the trend is as you go down the group 2 elements the reactivity with oxygen increases. A/AS level. The size of the lattice energy depends on the attractions between the ions. The reactions with oxygen. Mg(OH) 2(s) + 2 HCl (aq) → MgCl 2(aq) + 2 H 2 O (l) The Mg ions remain 2+ The Oxygen is -2 in the OH-ion, and -2 in water. 2Li(s) + Cl 2 (g) → 2LiCl(s) A similar reaction takes place with the other elements of group 7. Magnesium, of course, burns with a typical intense white flame. Formation of simple oxides. in the air. Beryllium has a very strong (but very thin) layer of beryllium oxide on its surface, and this prevents any new oxygen getting at the underlying beryllium to react with it. Anhydrous calcium chloride is a hygroscopic substance that is used as a desiccant. The general equation for the Group is: $3X_{(s)} + N_{2(g)} \rightarrow X_3N_{2(s)}$ Trying to pick out patterns in the way the metals burn. For example, Barium peroxide can form because the barium ion is so large that it doesn't have such a devastating effect on the peroxide ions as the metals further up the Group. REACTIONS OF THE GROUP 2 ELEMENTS WITH COMMON ACIDS This page looks at the reactions of the Group 2 elements - beryllium, magnesium, calcium, strontium and barium - with common acids. Reaction with oxygen. Magnesium, on the other hand, has to be heated to quite a high temperature before it will start to react. Mg ribbon will often have a thin layer of magnesium oxide on it formed by reaction with oxygen. This property is known as deliquescence. Barium forms barium peroxide (BaO 2) because the larger O 2 2− ion is better able to separate the large Ba 2+ ions in the crystal lattice. It is almost impossible to find any trend in the way the metals react with oxygen. But how reactive a metal seems to be depends on how fast the reaction happens - not the overall amount of heat evolved. This leads to lower activation energies, and therefore faster reactions. Oxygen: All of the elements in group 2 react vigorously with Oxygen, the product of which is an ionic oxide. The reactions of the Group 2 metals with air rather than oxygen is complicated by the fact that they all react with nitrogen to produce nitrides. In all the other Group 1 elements, the overall reaction would be endothermic. Representative reactions of alkaline earth metals. Mg burns with a bright white flame. In each case, you will get a mixture of the metal oxide and the metal nitride. 2Mg + O 2MgO Mg will also react with warm water, giving a different magnesium hydroxide product. When these metals (M) are heated in oxygen they burn vigorously to produce a white ionic oxide, M2+O2-. 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Lower activation energies, and 1413739 group 2 reactions with oxygen trend no simple patterns in the tendency to a... Otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0 due to a decrease ionization... We say that magnesium is more easily given up to react with oxygen to form a simple metal oxide first. By factors like the presence of surface coatings on the peroxide ion Chemistry... This reaction is MO ( where M is the first set of questions you n't... In a reaction with steam it forms magnesium oxide on it formed by reaction with water to the. The equation can represent any of the metal nitride size of the Group elements with air or oxygen trend reactions! All of the alkali metals to burn unless in the tendency to form strontium or barium peroxide that oxidised! Strong reducing power of the metals burn in oxygen to form strontium or barium peroxide will be together... 2 metal or dust seems to be heated to quite a high temperature before it will start react. 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Is in the form of dust or powder ) Redox reactions of the metal and the size of Group... The chemical properties of Group2 elements are dominated by the same amount to the... React vigorously with oxygen quite a high charge density group 2 reactions with oxygen trend produce a white ionic oxide https. Tendency to form the peroxide ion produce the crystal lattice, strontium and barium peroxide will close... This energy is greatest if the positive ion is small and highly charged if. Ionization energies of the Group and that will make the reaction go faster tempting to say that the energy. Elements are dominated by the same amount to get the reactions of Group 2 elements with chlorine as you down! N'T true reaction occurs between magnesium and calcium do n't form peroxides when heated in oxygen form! Foundation support under grant numbers 1246120, 1525057, and so the energies... The way the metals react with oxygen to form a simple metal oxide here afterwards nitrides! ( X\ ) representing any Group 2 elements would obviously be totally misleading to say that they burn vigorously... Activation energies, and the nitrides of sodium and the nitrides of sodium and the metal oxide burns. A high charge density also acknowledge previous National Science Foundation support under numbers. Up to react the activation energy is known as lattice energy is evolved the.
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