7.1 General structure of the Periodic Table.

Transcription

1 Chemistry Form 4 Page 1 Ms. R. Buttigieg 7.1 General structure of the Periodic Table. What you should know already Complete the passage using words from the list. You can use words more than once acidic alkaline calcium carbon dioxide chlorine copper hydrogen lead left magnesium magnesium oxide metals neutral neutralization nitrogen oxygen periodic table reactivity series right sodium hydroxide symbol zinc sulphate universal indicator 1. Each element can be represented by one or two letters called a. 2. Which element is represented by each of the following: Ca O Mg Cl Pb N 3. Elements are shown in the. 4. Most of the known metals are. 5. Metals are on the hand side and non-metals are on the hand side of the periodic table. Complete the following word equations: 6. Magnesium + Oxygen 7. Sodium + Water + 8. Zinc + Sulphuric Acid + 9. Magnesium + Copper (II) oxide Metals are arranged in order of reactivity in the Complete: 11. The ph of a solution can be found using a ph meter or. 12. A solution with a ph of 7 is. Solutions with a ph less than 7 is and greater than 7 is. 13. Reactions between acids and alkalis are reactions.

2 Chemistry Form 4 Page 2 Ms. R. Buttigieg See Books - Chemistry for You Chapters 4, 5, 6 GCSE Chemistry Chapter 3 pgs The table as a series of vertical Groups and horizontal periods. Rows of the Periodic table are called Periods Columns of the Periodic table are called Groups What is interesting however is that: Read Chemistry For You pg The number of electrons in the outer shell gives us the Group Number So all the elements, whose atoms have the same number of electrons in their outer shell, are grouped together. - The number of electron shells gives us the Period Number. a. In the modern periodic table, what are the elements arranged in order of? their first letter atomic number relative atomic mass b. What are the vertical columns called? periods trends groups

3 Chemistry Form 4 Page 3 Ms. R. Buttigieg The areas of the table, which contain reactive metals, transition metals, characteristic non-metals, and the noble gases. You should be able to identify these areas on an outline of the periodic table. I suggest you learn them well ok!!! See the periodic table on GCSE Chemistry pg. 40 See the periodic table on Chemistry for You pg. 43 and pg. 392 Work out Chemistry For You pg. 49 numbers 1, 5. pg. 73 number The noble gases as an unreactive group. Group 8 is also called Group 0 or the Noble Gas group. All the elements in this group have a full outer shell. So, they have no desire to lose or gain electrons so they are very stable and are very unreactive as a group. Until about 40 years ago it was believed that they never reacted. We now know that they form some compounds, e.g. xenon tetrafluoride, XeF 4 Some uses of the Noble gases (Revision Form 3) rely on their unreactivity Noble Gas Helium Neon Argon Krypton and xenon Radon Use Balloons and airships less dense than air Filling advertising tubes Filling electric light bulbs, inert atmosphere for welding Lighthouse and projector bulbs. Lasers Killing cancerous tumours

4 Chemistry Form 4 Page 4 Ms. R. Buttigieg Relating the Group number / electron configuration to metallic / non- metallic character. Elements of group 1, 2, 3 that give away 1, 2 and 3 electrons respectively are the metals. Elements of groups 6, 7 that accept 2 and 1 electrons respectively are the non-metals. Read Chemistry for You pg The metalloids (e. g. silicon and germanium). The metalloids are not as good a set of conductors as the metals, but they are better conductors than the nonmetals. Many of them are known as semiconductors. Also, unlike the metals, which become better conductors at low temperatures, the metalloids become better conductors at higher temperatures. Because of their unique electrical conductivity, the metalloids have drawn a lot of attention from the computer and electronics industries. When involved in chemical bonding, the metalloids again exhibit middle-of-the-road qualities. They are capable of taking electrons from most metals and will readily lose electrons to most nonmetals. Their electronegativity values are also mid-range. So it is unlikely for them to be involved in ionic bonding. They will usually establish covalent bonding when found in compounds.

5 Chemistry Form 4 Page 5 Ms. R. Buttigieg Here is a list of elements. Use your periodic table to answer these questions. Chlorine, helium, lithium, magnesium, titanium 1. Which element is in period 1? 2. Which element is in group 2? 3. Which element is an alkali metal? 4. Which element is a halogen? 5. Which element is a transition metal? 6. Which element is a noble gas? 7. Which elements have atoms containing 2 electrons in the outer energy levels?, 8. Which two of these elements are in the same period of the periodic table?, 7.2 Trends in properties across a period (Na to Ar) Group Element Na Mg Al Si P S Cl Ar Character Metallic Metalloid Non-metallic Noble Gas Reactivity ----Decreases-----> - <----Decreases Structure of element Giant metallic Giant covalent Molecular Atomic Ion Na + Mg 2+ Al 3+ None P 3- S 2- Cl - None Oxide Na 2 O MgO Al 2 O 3 SiO 2 P 2 O 5 P 2 O 3 SO 2 SO 3 Cl 2 O None Type of Strongly basic amphoteric Acidic None oxide Structure of oxide Giant ionic Giant covalent Molecular None o Change from metallic to non-metallic character across a period From left to right across a period, there is a transition from metals to nonmetals. o Note the change in reactivity o Note the type of ions formed. (valency) o Note the type of bonding From left to right across a period the bonding in chlorides or oxides changes from ionic (with metals e.g. Na + Cl - ) to covalent (with non-metals e.g. SO 2 ). o Note the compounds they form From left to right across a period the oxides change from alkaline/basic (with metals e.g. Na 2 O) to acidic (with non-metals e.g. SO 2 ). Note the change from basic, through amphoteric to acidic nature.

6 Chemistry Form 4 Page 6 Ms. R. Buttigieg How the number of electrons changes across a period GROUP NUMBER As you can note after drawing the missing electrons, the number of electrons increases as you move to the right of the period. (In reality note that the radius of the atom becomes a bit smaller) This is what causes the change in the properties of the elements as you move across a period. 7.3 Trends down typical metallic groups Group 1 Metals Group 1 elements all have one electron in the outer shell or energy level. Group 1 contains very reactive metals including lithium, sodium and potassium. They are so reactive that they have to be stored in oil to prevent them from reacting with the air. These are not typical metals because they tend to be soft and light. They also have low melting and boiling points. If a new group 1 element was discovered which 2 of these properties would it have? It would be a metal with high melting and boiling point. It would be a metal with low melting and boiling point. It would be a gas with low melting and boiling point. It would react with water to form an alkaline solution. It would react with water to form an acidic solution and hydrogen.

7 Chemistry Form 4 Page 7 Ms. R. Buttigieg This trend shows that as you go down Group 1, the elements become more reactive. Remember, all Group 1 elements have just one electron in their outer energy level. When they react they lose this electron. By doing this, they obtain a full outer energy level. They become more stable because they now have the electron structure of a noble gas. Lets take sodium as an example. A sodium atom has 11 protons in the nucleus surrounded by 11 electrons. When the sodium atom reacts and becomes a sodium ion, it loses one electron. There are now 11 protons in the nucleus surrounded by 10 electrons, so the overall charge on the ion will be 1+. The sodium ion is written as Na+. Na+ is a positive ion. The outer shell is full, so the ion is stable. The smaller an atom, the closer its outer electron is to the nucleus, and the more difficult it is to remove. This is because there is a strong attractive force on it from the positive protons in the nucleus. As you go down the group, the size of the atoms increases and the outer electron gets further away from the nucleus and therefore becomes easier to remove. This means that as you go down the group, the reactivity increases.

8 Chemistry Form 4 Page 8 Ms. R. Buttigieg Electronegativity is the measure of the ability of an atom or molecule to attract electrons in the context of a chemical bond. Occurrence and Extraction These elements are too reactive to be found free in nature. Sodium occurs mainly as NaCI (salt) in sea-water and dried-up sea beds. Potassium is more widely distributed in minerals such as sylvite, KCI, but is also extracted from sea-water. The alkali metals are so reactive they cannot be displaced by another element, so are isolated by electrolysis of their molten salts. Burn vigorously in air to form the oxide: The oxides formed are white. Flame colours are different. Li red Na yellow K lilac Rb red Cs blue a) Lithium (s) + Oxygen (g) Lithium oxide (s) b) The alkali metal oxides then dissolve in water to form alkali solutions Li 2 O (s) + H 2 O (l) 2 LiOH (aq) Reaction with water: These are strongly alkaline solutions and because of this these elements are also called the alkali metals. Lithium reacts smoothly with cold water. It moves about on the surface of the water. A solution of Lithium hydroxide is formed and hydrogen gas is given off. Lithium (s) + Water (l) Lithium hydroxide (aq) + hydrogen (g) Sodium reacts vigorously with cold water. It moves about on the surface of the water & melts into a silvery ball. A solution of Sodium hydroxide is formed and hydrogen gas is given off. Potassium reacts violently with cold water. It moves about on the surface of the water & melts into a silvery ball, then catches fire. It burns with a lilac flame.

9 Chemistry Form 4 Page 9 Ms. R. Buttigieg Group 2 Metals Group 2 elements all have one electron in the outer shell or energy level. Harder then Group 1 Silvery-grey Good conductors Burn in air to form the oxides. Less reactive than their neighbor Group 1 Metals In group 2 we find magnesium and calcium. Both are metals. But calcium is more reactive than magnesium. (as it has more shells). Calcium reacts steadily with cold water. It falls to the bottom, giving off hydrogen and forming calcium hydroxide. Calcium hydroxide is slightly soluble in water. So the solution becomes cloudy due to the formation of undissolved calcium hydroxide. Calcium (s) + Water (l) Calcium hydroxide (aq) + Hydrogen (g) Calcium reacts vigorously with acids. Calcium (s) + Hydrochloric acid (aq) Calcium Chloride (aq) + Hydrogen (g) Magnesium reacts slowly with water, fast with steam and fast with acids. A piece of clean magnesium ribbon is placed in water and a test tube full of water is inverted over it. It takes several days to collect some hydrogen gas in the test tube. Magnesium (s) + Water (l) Magnesium hydroxide (aq) + Hydrogen (g) Magnesium reacts vigorously with steam. Steam is passed over the heated magnesium. The Magnesium reacts by glowing white and forms white magnesium oxide powder. Hydrogen is formed which can be lighted at the opening of the glass tubing. Magnesium (s) + Steam (l) Magnesium hydroxide (aq) + Hydrogen (g) Strontium & Barium also react well with water. is the more reactive of the two. See GCSE Chemistry pg. 44, Chemistry for You pg Work out Chemistry for You: Pg. 60 number 3 (You need a graph paper) Pg. 74 number11, 13, 15b,17.

10 Chemistry Form 4 Page 10 Ms. R. Buttigieg A. Underline the correct word/s: 1. Metals are electropositive/electronegative. 2. Non-metals are electropositive/electronegative. 3. Metals react by giving/receiving/sharing electrons. 4. Non-metals react by giving/receiving/sharing electrons. 5. Down a group electronegativity increases/decreases. 6. Across a period electronegativity increases/decreases. 7. Non-metals are found on the right/left hand side of the table. 8. Group 1 are called the. 9. Group 1 are called the. 10. Group 1 are called the. 11. The shallow block in the table are the. 12. Group 8/0 are called the. B. Complete the table below: (the first one has been done for you) Group Element Na Mg Al Si P S Cl Ar Character metal Electron 2, 8, 1 configuration Valency 1 Ion Na + Oxide Type of oxide Structure of oxide Na 2 O basic Giant ionic C. Write the chemical equations for the given word equations: (don t forget state symbols) Sodium + Water sodium hydroxide + hydrogen Magnesium + Oxygen Magnesium Oxide Calcium + Hydrochloric Acid Calcium Chloride + Hydrogen

11 Chemistry Form 4 Page 11 Ms. R. Buttigieg JUNIOR LYCEUM ANNUAL 2002 Elements in the same Group of the Periodic Table show a similarity in physical and chemical properties. The elements also show a trend in reactivity. Barium is in Group 2 of the Periodic Table. Use your knowledge of the Group 2 metals (e.g. Mg, Ca) to answer the following questions about Barium. (a) (i) What is the number of electrons in the outer shell of a barium atom? (ii) Write down the formula for the barium ion. (2 marks) (b) Predict one physical property that you would expect barium to show. (1 mark) (c) How would you expect barium to be extracted from its compounds? (1 mark) (d) (i) State one thing you would expect to see when barium is added either to water, or to dilute hydrochloric acid. (1 mark) (ii) Give a balanced equation for the reaction of barium - with water, with dilute hydrochloric acid. (4 marks) (e) Would you expect barium to be more, or less reactive, than magnesium and calcium? (1 mark) 2. (a) (i) What are allotropes? (2 marks) (ii) Name the two allotropes of carbon. (2 marks) 3. Consider the following pairs of elements : sodium and potassium ; magnesium and calcium (a) For EACH pair; give two typical PHYSICAL properties which are similar for both elements. (4 marks) (b) For EACH pair describe fully a reaction, including the observations and equations, which show that both elements have similar CHEMICAL properties. (8 marks)

12 Chemistry Form 4 Page 12 Ms. R. Buttigieg 7.4 The Transition Metals Read Chemistry For You: Transition Elements pg. 56, 57 v.important Extraction of Iron (Blast furnace) pg make sure you know all the equations for the blast furnace reactions The transition metals are found in the large block between Groups 2 and 3 in the periodic table Common properties of the TRANSITION ELEMENTS: 1. They are metals 2. They are hard and strong 3. Have high melting points (except mercury) and densities 4. Have variable valency (charge on ion) e.g. Iron (II) and Iron (III) valency 2 or Form coloured compounds These include blue copper(ii) sulphate and orange-brown rust (a type of iron oxide). 6. Many of them have catalytic activity Catalysts make reactions go faster without being used up during the reaction. Transition metals such as platinum and rhodium are found in catalytic converters. 7. Good conductors of heat and electricity 8. Can be hammered or bent into shape easily 9. Less reactive than alkali metals like sodium Some examples: Work out: Chemistry for You page 60 number 1; page 61 number 8 Page 99 number 5. (see pg. 91 to help you answer).

13 Chemistry Form 4 Page 13 Ms. R. Buttigieg 1. Iron is extracted in a Blast Furnace (a) (i) Name two raw materials that go into a Blast Furnace. (ii) Name two substances, (apart from iron), that come out of a Blast furnace. (4 marks) (b) Most of the iron leaving the furnace is converted into steel. (i) Give one reason why pig iron is not as useful as steel. (ii) Give one use of steel and state the property upon which this use depends (3 marks) 2. Give the letter of the area in which you would find (Junior Annual 2001) A) Give the letter of the area in which you would find i) elements that do not tend to form compounds ii) the most reactive metals iii) a metal which is borderline with non-metals and whose oxide is amphoteric iv) a solid non-metal that burns in air to form an acidic oxide v) a metal that has a variable valency and forms coloured ions vi) a halogen vii) an element that reacts with water to form an alkaline solution B) Give the number of electrons in the outer shell of the atoms of i) most noble gases ii) metals that form ions of the type X 2+ iii) non-metals that form ions of the type X - (10 marks)

14 Chemistry Form 4 Page 14 Ms. R. Buttigieg How does the blast furnace work? The Blast Furnace is a large steel structure about 30 metres high. It is lined with refractory firebricks that can withstand temperatures approaching 2000 o C. The furnace gets its name from the method that is used to heat it. Pre-heated air at about 1000 o C is blasted into the furnace through nozzles near its base. The largest Blast Furnaces in the UK produce around tonnes of iron per week. The largest on in Europe, has produced up to tonnes per day ( tonnes per week) but is currently running at 8000 tonnes per day. This is equivalent to all the iron needed for about 5 cars every minute. Refining iron The metal that leaves the Blast Furnace contains between 4% and 5% of carbon. This much carbon makes a very hard but brittle metal which is not much use. The next step in the production of steel is to reduce the levels of carbon and other impurity elements in the hot metal.

15 Chemistry Form 4 Page 15 Ms. R. Buttigieg Make sure you know: The principle of extraction from haematite in the Blast furnace, including function of limestone in removing main impurity. - uses of pig iron and steel related to the difference in their physical properties. - Revise rusting and its prevention (it s the opposite of what happens in the blast furnace) Pig iron is an alloy containing about 3% carbon with varying amounts of S, Si, Mn, and P. It is hard, brittle, fairly fusible, and is used to produce other alloys, including steel. Steel is a mixture of iron and carbon. The amount of carbon may range from 0 1% to 1 5% giving steels of different properties. Steel is used to make machinery, tools, cars, large girders and bridges. Oxidation Oxidation Is Loss of electrons Reduction Reduction Is Gain of electrons OIL RIG (see Chem 4 U pg. 115) Iron and Copper - both are transition metals. Iron (II) compounds are green. Iron (III) compounds are brown. Copper (I) compounds are red Copper (II) compounds are blue. Iron exhibits a valency of 2 and 3 e.g. Iron(II)sulphate FeSO 4 and iron(iii)sulphate Fe 2 (SO 4 ) 3 Copper exhibits a valency of 1 and 2 e.g. Copper (I) chloride CuCl and Copper(II)chloride CuCl 2 And copper(i)sulphate Cu 2 SO 4 and copper(ii)sulphate CuSO 4. To make Iron (II) chloride, iron is reacted with hydrochloric acid or hydrogen chloride is passed over heated iron. Fe (s) + 2HCl (aq) FeCl 2 (aq) + H 2 (g) Fe (s) + 2HCl (g) FeCl 2 (s) + H 2 (g) To make Iron (III) chloride, iron is reacted with chlorine. The Iron is heated to start the reaction: 2Fe (s) + 3Cl 2 2FeCl 3 (s) When you convert and iron(ii) compound into an iron (III) compound, you are oxidizing iron (II) into Iron (III). Fe ++ - e - Fe +++ oxidising is loosing electrons

16 Chemistry Form 4 Page 16 Ms. R. Buttigieg To convert an iron(iii) compound into and iron (II) compound, a reducing agent is needed. Fe e - Fe ++ Reduction is gaining electrons You can use oxidising agents like sulphur dioxide and hydrogen sulphide. When you bubble sulphur dioxide through iron (II) compound solution, the brown solution turns to pale green. Copper will react with oxygen in the air to form copper(ii) oxide. copper + oxygen copper(ii) oxide. 2Cu (s) + O 2(g) 2CuO (s) Reaction of copper with acids Copper metal dissolves in hot concentrated sulphuric acid to form solutions containing the aquated Cu(II) ion together with hydrogen gas, H 2. Cu(s) + H 2 SO 4 (aq) Cu 2+ (aq) + SO 4 2- (aq) + H 2 (g) Copper metal also dissolves in dilute or concentrated nitric acid, HNO 3 Triiron tetraoxide and hydrogen are formed when iron reacts with steam. (a) Label the diagram below, which shows a set up suitable for carrying out the reaction in the laboratory. Complete the diagram to show how a test-tube of the hydrogen given off can be collected. (5 marks) (b) The unbalanced equation for the reaction of iron with steam is shown below: Balance the equation Fe + H 2 O Fe 3 O 4 + H 2 (c) Cobalt is a transition metal. State two properties you would expect cobalt to have, which are typical of a transition metal.

17 Chemistry Form 4 Page 17 Ms. R. Buttigieg 7.5 The Halogens Group 7 Read Chemistry For You: Group 7 the halogens pg GCSE Chemistry: Group 7 the Halogens pg Fluorine and chlorine are poisonous gases, bromine is a brown, fuming liquid and iodine an almostblack solid with a poisonous purple vapour.

18 Chemistry Form 4 Page 18 Ms. R. Buttigieg All the halogens: Are coloured and become darker as you go down the group Are found as molecules and form molecular (covalent) compounds with other non metals like hydrogen e.g HCl. With Hydrogen the hydrogen halides are formed, they dissolve in water to form acidic solutions (ph < 7) e.g. H 2 (g) + Cl 2 (g) 2HCl (aq) The molecules are diatomic (2-atom) molecules, namely Br 2, F 2, Cl 2, I 2, Reactions with water: Chlorine reacts with water to form 2 acids hydrochloric acid and hypochlorous acid (bleach) Bromine is less acidic than chlorine. Cl 2 (g) + H 2 O (l) HCl (aq) + HOCl (aq) Iodine is weaker still. (almost insoluble in water but made soluble in the presence of potassium iodide solution KI) Reactions with Group I and II metals: The others react in more or less the same way.

19 Chemistry Form 4 Page 19 Ms. R. Buttigieg Reactions with Iron When iron wool is heated with chlorine, the iron glows brightly, and reacts vigorously to produce a brown smoke. Brown iron chloride is left behind. 2Fe (s) + 3Cl 2 (g) 2FeCl 3 When iron is heated with Iodine the iron glows even less brightly than with bromine, but brown smoke and brown iron iodide are left behind. Bleaching effect on water containing an indicator; Chlorine bleaches damp litmus and is very reactive. Chlorine reacts with water, forming hypochlorous acid. Cl 2 (g) + H 2 O (l) HOCl (aq) + HCl (aq) Hypochlorous acid is a very reactive compound that readily give sup its oxygen to the dye, to form a colourless compound. HOCl (aq) + dye or indicator HCl + (dye + O colourless) The product must then be thoroughly washed to remove HCl or it will be attacked by the free acid. o Bromine is also a bleaching agent but not as rapid as chlorine. o Iodine does not bleach. Displacement Reactions If chlorine is bubbled into a solution of potassium bromide, then the less reactive halogen, bromine, is displaced by the more reactive halogen, chlorine. 2KBr (aq) + Cl 2 (g) 2KCl (aq) + Br 2 (aq) Chlorine gives salts called chlorides. Bromine gives salts called bromides. Work out GCSE Chemistry pg. 48 numbers 1 and 2

20 Chemistry Form 4 Page 20 Ms. R. Buttigieg Iron can form two chlorides. (a) When dilute hydrochloric acid is reacted with iron, a pale green iron chloride solution is formed. Hydrogen is also liberated. (i) What is the valency of iron in this chloride? (1 mark) (ii) Write a balanced equation for this reaction. (2 marks) (b) When sodium hydroxide is added to a solution of the green iron chloride, a green precipitate is formed. This precipitate goes darker on standing. (i) Give an equation to show the formation of the green precipitate. (2 marks) (ii) Why does the precipitate darken on standing? (1 mark) (c) When chlorine is passed over heated iron, a brown iron chloride is formed. (i) What is the valency of iron in this chloride? (1 mark) (ii) Give a reason why chlorine gives this brown chloride with iron, not the same chloride formed with dilute hydrochloric acid. (1 mark) (d) Iron is a transition metal. Write down two properties which are typical of a transition metal, and that are illustrated in the above reactions. (2 marks) (e). Consider the following list of metals. Zn, Mg, Cu, Ag, Fe, Al. Rewrite this list of metals, starting with the most reactive. (2 marks)