In the early version of the periodic table (by Newlands and then Mendeleev), how were the elements arranged?

Transcription

1 Page 1 In the early version of the periodic table (by Newlands and then Mendeleev), how were the elements arranged? What can we say about the elements in the same group of the periodic table? Why is the periodic table called the periodic table? What was the problem with the early periodic table, where elements were arranged in order of atomic weight? When Mendeleev proposed his early periodic table, what problem did he highlight? How did Mendeleev adjust his periodic table to take into account the problems he identified? How are the elements arranged in the modern periodic table? Which group was not featured on the early periodic table? What can we say about the electronic structure of elements in the same group of the periodic table? What do we call the elements in group 1 of the periodic table? What can we say about the density of the elements in group 1 (the alkali metals)? How do group 1 (alkali metals) react with non-metals?

2 Page 2 Elements in the same group of the periodic table have similar chemical and physical properties. In the early version of the periodic table (by Newlands and then Mendeleev), the elements were arranged by atomic weight. In the early periodic table, where elements were arranged in order of atomic weight, some elements were clearly in the wrong group (based on their properties). The periodic table is called the periodic table because elements with similar properties occur at regular intervals. Mendeleev sometimes switched the order of the elements if they were clearly in the wrong group. He also left gaps for elements which he realised had not been discovered. When Mendeleev proposed his early periodic table, he realised that some elements had not been discovered. Group 0 was not featured on the early periodic table as the group 0 (noble gases) had not been discovered In the modern periodic table, elements are arranged in order of atomic (proton) number. Now, all the elements were in the appropriate groups. Elements in group 1 of the periodic table are called the alkali metals. Group 1 (alkali metals) react with nonmetals to form ionic compounds. The alkali metal ion has a charge of +1. The compounds produced are white solids that dissolve in water, forming colourless solutions. Elements in the same group of the periodic table have the same number of electrons in their outer energy level (apart from group 0, where helium has 2 and the rest have 8). All of the elements in group 1 (alkali metals) are metals with low density (Li, Na, K are less dense than water).

3 Page 3 How do group 1 (alkali) metals react with water? What happens as we move down group 1, in terms of: reactivity of the elements melting and boiling points What can we say about transition metals compared to the metals in group 1. State three facts about transition metals. What do we call the elements in group 7? How do the halogens react with metals? What happens as we move down group 7, in terms of: reactivity of the elements melting and boiling points Complete this sentence: A more reactive halogen can.. a less reactive halogen from an aqueous solution of its salt What happens in the following reaction? chlorine + lithium bromide What happens in the following reaction? chlorine + lithium fluoride Explain why group 1 (alkali) metals become more reactive as we move down the group. Explain why group 7 elements (halogens) become less reactive as we move down the group.

4 Page 4 As we move down group 1, The elements get more reactive The melting and boiling points decrease Group 1 (alkali) metals react with water releasing hydrogen. They form hydroxides which dissolve in water, forming an alkaline solution. Many transition metals Can have ions with different charges Form coloured compounds Are useful as catalysts Compared to group 1 metals, transition metals: Are denser Have higher melting points (apart from mercury) Are stronger and harder Are much less reactive Do not react as vigorously with water and oxygen Halogens react with metals to form ionic compounds. The halogen ion (now called a halide) has a charge of -1. Elements in group 7 are called the halogens. A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt As we move down group 7, the elements get less reactive the melting and boiling points increase chlorine + lithium fluoride chlorine + lithium fluoride chlorine + lithium bromide bromine + lithium chloride Chlorine is less reactive than fluorine so it cannot displace the fluorine from the lithium fluoride. Chlorine is more reactive than bromine so it displaced the bromine from the lithium bromide. Group 7 elements (halogens) get less reactive as we move down the group because an electron is less easily gained into the outer energy level. The outer electron is further from the nucleus. Internal energy levels shield the outer electron from the nucleus. Group 1 (alkali) metals get more reactive as we move down the group because the outer electron is more easily lost. The outer electron is further from the nucleus. Internal energy levels shield the outer electron from the nucleus.

5 Page 5 How can we determine the hardness of a sample of water? How do soapless detergents react with hard water? What makes hard water hard? How is hard water formed? What is meant by temporary hard water? How can we tell the difference between permanent hard water and temporary hard water? How can hard water cost us money? What are the benefits of hard water? How can we soften hard water using sodium carbonate? How can we soften water using a water softener? State the three stages of preparing drinking water. Water filters contain carbon, silver and ion exchange resins. Describe the functions of these.

6 Page 6 Soapless detergents do not form a scum with hard water. They form a lather. Hard water forms a scum (rather than a lather) with soap so if a sample of water is very hard, it will need more soap to form a lather. The amount of soap needed to form a lather indicates the hardness of the water. When water flows over rocks containing calcium or magnesium compounds, these can dissolve in the water, making it hard. Hard water is hard because it contains dissolved compounds of calcium or magnesium. If we boil temporary hard water, it becomes soft. However, boiling permanent hard water has no effect on the hardness. Temporary hard water contains hydrogencarbonate ions (HCO3 - ). If we boil this water, these form carbonate ions. The carbonate ions react with the calcium ions / magnesium ions, forming a precipitate. This removes the calcium ions / magnesium ions from solution which makes the water soft. Hard water can contain calcium ions. These help us to develop strong bones and teeth. Calcium ions can also decrease the risk of heart disease. Hard water requires more soap to develop a lather. Also when temporary hard water is heated it forms scale (precipitate of calcium carbonate or magnesium carbonate). Scale reduces the efficiency of heating systems and kettles. Water softeners carry out ion-exchange. They contain either hydrogen ions or sodium ions. When hard water passes through, the calcium ions / magnesium ions in the water are switched for the hydrogen ions / sodium ions, making the water soft. If we add sodium carbonate to hard water, the carbonate ions react with the calcium ions /magnesium ions. This forms a precipitate, removing these ions from solution. This makes the water soft. Carbon removes impurities such as chlorine. Silver kills microbes. Ion exchange resins make hard water soft. Select a source of water e.g. an unpolluted river. Filter out any solids. Add chlorine to sterilise the water (kill microbes).

7 Page 7 Why is fluoride added to drinking water and why do some people object to this? How can completely pure water be produced? Which equation can we use to determine the amount of heat energy released / taken in during a reaction. We can measure the energy released from burning a fuel by using a calorimeter. State two issues with this. When we measure the energy change of a chemical reaction, why should we use a polystyrene cup rather than a glass beaker? Draw an energy level diagram for an exothermic reaction. Label the activation energy. Draw an energy level diagram for an endothermic reaction. Label the activation energy. Describe the bond energy changes that take place during a chemical reaction. What can we say about the bond energy changes taking place in an endothermic reaction? What can we say about the bond energy changes taking place in an exothermic reaction? How do catalysts speed up chemical reactions? Draw an energy level diagram showing the effect of a catalyst on a chemical reaction.

8 Page 8 Completely pure water can be produced by distillation. However, this requires a great deal of energy and is therefore extremely expensive. Adding fluoride to drinking water improves dental health. However, some people object as it prevents people from choosing whether they want to drink water with fluoride. 1. A great deal of heat energy is simply passed into the air, rather than the water in the calorimeter. 2. We should use a metal calorimeter rather than a glass beaker as metal is a better conductor of heat than glass. Q = m c ΔT Q = energy (J) m = mass (g) c = specific heat capacity (J/g/ o C) ΔT = temperature change ( o C) Polystyrene is a better insulator than glass. If we used a glass beaker then heat energy could pass in or out of the solution, giving us an incorrect reading. Breaking bonds requires energy (endothermic). Making bonds releases energy (exothermic). In an exothermic reaction, the energy released by forming new bonds is greater than the energy needed to break existing bonds. In an endothermic reaction, the energy needed to break existing bonds is greater than the energy released from forming new bonds. Catalysts provide a different pathway for a chemical reaction with a lower activation energy.

9 Page 9 State the equation for the combustion of hydrogen in engines. What happens when hydrogen is used in a fuel cell. State the advantages and disadvantages of using hydrogen in a fuel cell compared to combusting hydrogen in an engine. How can we test for calcium and magnesium ions by using sodium hydroxide solution? State the flame test results for the following metal ions: lithium sodium potassium calcium barium How can we test for aluminium ions by using sodium hydroxide solution? State the colours of the precipitates formed when the following ions react with sodium hydroxide solution: copper (II) iron (II) iron (III) How can we test for a metal carbonate (eg sodium carbonate)? How can we test for halide ions? What are the colours of the positive results? Describe how we can test for sulfate ions? Describe how we can use titration to determine the concentration of an acid or alkali. State the raw materials for producing ammonia by the Haber process and describe their sources.

10 Page 10 In a fuel cell, hydrogen reacts with oxygen to make water. This also produces electricity. The electricity can be used to power a vehicle. hydrogen + oxygen water (+energy) lithium = crimson sodium = yellow potassium = lilac calcium = red barium = green Hydrogen fuel cells are more efficient than combusting hydrogen. The water produced from a hydrogen fuel cell can be used for drinking water (eg in a space station). Hydrogen fuel cells require expensive catalysts. Aluminium ions will produce a white precipitate when reacted with sodium hydroxide solution. If we add excess sodium hydroxide solution, the white precipitate will redissolve. Both calcium and magnesium ions will produce a white precipitate when reacted with sodium hydroxide solution. First we add any dilute acid. Bubbles of gas will be produced. If we pass the gas through limewater and the limewater turns cloudy, the gas is carbon dioxide. This tells us that we had a metal carbonate. copper (II): blue precipitate iron (II): green precipitate iron (III): brown precipitate We can test for sulfate ions by adding barium chloride solution in the presence of hydrochloric acid. Sulfate ions will produce a white precipitate. We can test for halide ions by adding silver nitrate solution in the presence of dilute nitric acid. chloride ions = white precipitate bromide ions = cream precipitate iodide ions = yellow precipitate Nitrogen is extracted from the air. Hydrogen is extracted from natural gas (or by electrolysis of water). Fill a burette with the acid Use a pipette to measure a known volume of alkali into a conical flask Place the conical flask onto a white tile Add indicator to the alkali (eg phenolphthalein) Gradually add the acid, while swirling the alkali Add the acid in drops as you approach the endpoint Record the final volume of acid needed

11 Page 11 State the conditions for producing ammonia by the Haber process. What is meant when a reversible reaction reaches equilibrium? What happens to the yield of an exothermic (reversible) reaction if we increase the temperature? What happens to the yield of an endothermic (reversible) reaction if we increase the temperature? What happens to the yield of an exothermic (reversible) reaction if we decrease the temperature? What happens to the yield of an endothermic (reversible) reaction if we decrease the temperature? What happens to a gaseous reversible reaction if we increase the pressure? Describe how the conditions of the Haber process are a compromise. State the structural formula of methanol. State the structural formula of ethanol. State the structural formula of propanol. What is the functional group of the alcohols?

12 Page 12 When a reversible reaction reaches equilibrium, both the forward and reverse reactions are taking place at the same rate. If we increase the temperature of an endothermic (reversible) reaction, the yield increases. 200 atmospheres pressure 450 o C Iron catalyst The ammonia is liquified by cooling and removed Unreacted gases are recycled back over the catalyst If we increase the temperature of an exothermic (reversible) reaction, the yield falls. If we decrease the temperature of an endothermic (reversible) reaction, the yield falls. If we decrease the temperature of an exothermic (reversible) reaction, the yield increases. We can favour the forward reaction by Increasing the pressure as there are fewer molecules on the right hand side Using a relatively low temperature as the forward reaction is exothermic However, a low temperature makes the reaction rate slow (ie a compromise). Using an iron catalyst increases the rate. If we increase the pressure of a gaseous reversible reaction, the position of the equilibrium shifts to the side with the fewest molecules. Ethanol has the following structural formula CH3CH2OH Methanol has the following structural formula CH3OH The functional group of the alcohols is OH Propanol has the following structural formula CH3CH2CH2OH

13 Page 13 Draw the structural formula of methanol. Draw the structural formula of ethanol. Draw the structural formula of propanol. State three uses of alcohols. What happens when alcohols are dissolved in water? What is produced when alcohols are reacted with sodium? Alcohols burn in air. True or false? How can alcohols be oxidised? What is vinegar and how is it produced? What is the functional group of carboxylic acids? What is the structural formula of methanoic acid? What is the structural formula of ethanoic acid?

14 Page 14 Ethanol Methanol Alcohols are used as fuels and solvents. Ethanol is found in alcoholic drinks. Propanol When alcohols are reacted with sodium, hydrogen gas is produced. When alcohols are dissolved in water, they form a neutral solution. Alcohols can be oxidised using chemical oxidising agents or by bacteria. When alcohols are oxidised, they form carboxylic acids. True: alcohols burn in air. The functional group of carboxylic acids is COOH Vinegar is a dilute solution of ethanoic acid in water. It is made by allowing bacteria to oxidise ethanol. The structural formula of ethanoic acid is CH3COOH The structural formula of methanoic acid is HCOOH

15 Page 15 What is the structural formula of propanoic acid? What is the displayed formula of methanoic acid? What is the displayed formula of ethanoic acid? What is the displayed formula of propanoic acid? What type of solution is produced when a carboxylic acid is dissolved in water? What is produced when carboxylic acids react with a metal carbonate. What is produced when carboxylic acids react with alcohols in the presence of an acid catalyst (eg sulfuric acid)? Carboxylic acids are weak acids. What does this mean? Why are esters used as flavourings and perfumes? What is the ester functional group? Draw the structure of the ester ethyl ethanoate. How is ethyl ethanoate produced?

16 Page 16 Methanoic acid The structural formula of propanoic acid is CH3CH2COOH Propanoic acid Ethanoic acid Carboxylic acids react with metal carbonates to produce carbon dioxide. When dissolved in water, carboxylic acids form an acidic solution. Weak acids (such as carboxylic acids) do not ionise completely when dissolved in water. This means that they have a higher ph (eg ph 5) than strong acids (which could be ph 1) when at the same concentration. In the presence of an acid catalyst (eg sulfuric acid), carboxylic acids react with alcohols to produce an ester. The ester functional group is: COO Esters are volatile (easily evaporate). They also have distinctive smells. Ethyl ethanoate is produced by reacting ethanol and ethanoic acid in the presence of an acid catalyst (eg sulfuric acid).