The Periodic Table of Elements

Transcription

1 The Periodic Table of Elements Notes The Periodic Table Elements are arranged in order of proton numbers Vertical columns of elements are called groups Horizontal rows of elements are called periods Across the period, the elements change from metals to non-metals Elements close to the staircase line, like silicon or germanium, can have some properties of the metals and of the non-metals --> metalloids Group number: indicates number of electrons in the outermost shell of an atom Period number: indicates the number of electron shells in an atom Metals always from positive ions while non-metals always form negative ions Source: Group I and II metals Properties Group I : alkali metals Group II: alkaline earth metals reactive reactivity increases down the group

2 Metalloids- elements close to the staircase line have properties of both metals and non-metals metalloids beneath the staircase line are called Poor Metals (eg tin and lead) Non-metals often gases (except Br, P, S, C, B, Se) low melting points poor conductors of heat and electricity (except graphite) form mainly covalent compounds Transition metals typical metals strong and hard good conductors of heat and electricity high melting points many of these metals have variable oxidation state eg Copper(I) and Copper(II), Iron(II) and Iron(III) not very reactive compounds formed often have characteristic colours. Examples: Copper(II) compounds are blue Iron(II) compounds are green Iron(III) compounds are yellow and green Manganate(VII) compounds are purple Dichromate compounds are orange transition metals and their compounds are used as catalysts to speed up industrial reactions. Examples: iron in Haber Process to manufacture ammonia Nickel used in manufacture of margarine from vegetable oils Platinum or vanadium(v) oxide in the Contact Process to manufacture sulphuric acid Periodic Law Elements in same group has the same number of valence shell electrons which the amount is the same as the group number. e.g. Group II has elements with valency of 2 electrons. The charges relates to the group number and number of valence electrons.

3 Elements on left side periodic table lose ions to form cation. Elements on right side periodic table gain ions to form anion Elements in Group IV can lose or gain electrons depending on reacting element. Transition metals may form variable cation of 2+ or 3+ Elements in same group form same type and number of bonds due to the same number of valence electrons. e.g. Sodium in Group I forms NaCl, so other elements in Group I does the same. (RbCl, KCl, LiCl, CsCl) From left to right, elements gradually change from metal to non-metal Elements close to dividing line in periodic table in back part of the note (in bold) are called metalloids having properties of metals and non-metals. Properties Trend down a group Trend across a period (Left to Right) Atomic size the size of the atom increases the size of atom decreases Ionization decreases down a group increases across a period energy* Electron affinity* decreases down a group increases across a period Electronegativity* decreases down a group increases across a period Electropositivity* increases down a group decreases across a period Ionization energy is the minimum amount of energy required to completely remove an electron from a gaseous atom The Electron affinity of a molecule or atom is the energy change when an electron is added to the neutral atom to form a negative ion. (in simple terms, it refers to how much an element loves an electron) Electronegativity is the tendency for an atom to attract electrons to itself Electropositivity is the tendency for an atom to lose an electron Changes in Group Proton number increase going down the group On each sides of periodic table, the change of the proton number small & gradual In transition metals, the gradual change is larger Using the Periodic Table Predicting Properties 1) Formula and Structures Given chlorine, iodine and bromine of Group VII forms molecules of Cl 2, I 2 and

4 Br 2 respectively, predict the molecular formula of Fluorine. eg. F 2 From example, we know elements in same group form same formula. 2) Properties of Elements Properties of element changes down the group. i.e. given list of Group 7 elements, predict the properties of astatine. Octet rule Cations - Metals form cations (position ions) - Cations are smaller than their atoms Anions - Non-metals form anions (negative ions) - Anions are larger than their atoms Isotopes - Have the same atomic number (number of protons) but different mass number or different number of neutrons Differences between metals and non-metals Metals Non-metals Usually solids at room temperature Often gases except:

5 except mercury High melting and boiling points (except Group I) Good conductors of heat and electricity Often shiny, ductile, malleable, and possess great tensile strength Bromine: liquid Sulphur: solid Phosphorus: solid Iodine: solid Carbon: solid Boron: solid Silicon: solid Low melting and boiling points (except B, C, Si) Poor conductors of heat and electricity (except carbon/graphite) Normally dull, soft, cannot be drawn out into wires or made into flat sheets Most compounds are covalent Oxides are usually neutral or acidic Most compounds are ionic Oxides are usually basic or amphoteric Often form hydrogen gas with Never form hydrogen gas from acids dilute acids Always form position ions (cations) Always form negative ions (anions) Group I metals called Alkali metals - the metals react with water to form alkaline solutions: the solutions turn red litmus paper blue have one outer shell electrons shiny, silvery solids soft, easily cut with scalpel low densities and melting points - these increases down the group good conductors of heat and electricity reacts easily in air so they're kept in oil chemically reactive - reactivity increases down the group (Caesium most reactive of all metals This is because the atoms become larger as we go down the group. It becomes easier for the outermost, single valence electron to escape to form an ion as the attractive force of the nucleus is further away and weaker have 1 valence electron loses one outermost electron to form an ion of +1 charge eg. Li +, Na +, K + react violently with air or oxygen, catching fire, and burning with characteristic

6 flame colors to form white oxides. To avoid this, the metals are stored under oil eg. 4K (s) + O 2 (g) ----> 2K 2 O (s) They also react vigorously with water, forming the alkaline hydroxide and releasing hydrogen gas eg. 2Na (s) + 2H 2 O (l) ---> 2NaOH (aq) + H 2 (g) Because alkali metals are such reactive metals, they combine directly with reactive non-metals such as the halogens to form salts eg. 2Na (s) + Cl 2 (g) ----> 2NaCl (s) Flame colour Alkali metal Flame color Li red Na yellow K lilac Rb - Reactions of the Alkali metals Alkali metal lithium sodium Reaction with air (oxygen) burns with a red flame to give lithium oxide (white solid) 4Li + O > 2Li 2 O burns with a bright yellow flame to produce white sodium oxide 4Na + O 2 ---> 2Na 2 O potassium burns violently with a lilac colored flame to produce white potassium oxide 4K + O 2 ---> 2K 2 O Reaction with water floats on water and reacts quickly to produce lithium hydroxide and hydrogen gas 2Li + 2H 2 O ---> 2LiOH + H 2 floats on water and reacts very quickly to produce sodium hydroxide and hydrogen gas 2Na + 2H 2 O ---> 2NaOH + H 2 floats on water and reacts violently to produce potassium hydroxide and hydrogen gas 2K + 2H 2 O ---> 2KOH + Reaction with chlorine burns with a bright flame to give a white solid of lithium chloride 2Li + Cl 2 ---> 2LiCl burns with a bright flame to give a white solid of sodium chloride 2Na + Cl 2 ---> 2NaCl burns vigorously in chlorine with a bright flame to give a white solid of potassium chloride 2K + Cl 2 ---> 2KCl

7 H 2 Group VII (Halogens) reactive non-metals have seven outer shell electrons poisonous low melting and boiling points - increases down the group elements become darker and solidify down the group reactivity decreases down the group because of their atomic size, which increases down the group therefore it becomes more difficult for the nucleus to attract an electron to form an ion most reactive is fluorine; least reactive is iodine all halogens form ions with single negative charge eg F -, Cl -, Br - Exists as diatomic molecules eg F 2, Cl 2, Br 2, I 2 reacts vigorously with metals to form ionic salts halogens become less reactive down the group Halogen Colour State Fluorine pale yellow gas Chlorine yellowish green gas Bromine red brown liquid Iodine shiny black solid Any halogen above another in the group will displace it from a solution of its salt -- --> displacement reactions This means that the more reactive halogen can take the place of the less reactive halogen of its salt. eg. Cl 2 + 2KBr -----> 2KCl + Br 2 When chlorine gas is bubbled through a colorless solution of potassium bromide, reddish brown color of bromine is seen. eg. Cl 2 + 2KI ----> 2KCl + I 2 When chlorine gas is bubbled through a colorless solution of potassium iodide, it turns brown and finally a black precipitate of iodine is formed. Group O (Noble/Inert Gases)

8 Exist as monatomic (single atom) least reactive elements in the gaseous state; do not form bonds low melting and boiling points have stable electronic configuration with full electrons on their shells chemically inert because the outermost shell of the element is full. It does not tend to combine with other elements, either covalently or ionically, and there is chemically inactive Name Helium Neon Argon Kryton Xenon Radon Uses in air ships, weather balloons in advertising lights an inert gas for electric bulbs, welding and making steel gas-filled electronic devices and lasers electronic flash guns natural radioactive gas Transition metals Element Common ions chromium 2- Cr 2 O 7 dichromate(vi) manganese MnO4 - manganate(vii) iron Fe 2+ iron(ii) Fe 3+ iron(iii) nickel Ni 2+ nickel(ii) copper Cu + copper(i)

9 Cu 2+ copper(ii) often form colored compounds can have variable oxidation states ---> no fixed number of valence electrons form complex ions eg MnO - 4 (manganate(vii) ions) high melting and boiling points high densities can have catalytic properties Industrial process Description Contact Process uses vanadium(v) oxide to help in the conversion to sulphur trioxide Haber Process uses an iron catalyst with iron oxide promoters to make ammonia gas Margarine manufacture uses nickel catalyst in the hydrogenation of alkene Uses of transition metals Transition metal Tungsten Chromium Titanium Manganese Nickel Zinc Copper Uses used in filaments of electric light bulbs as it is ductile and has a melting point over 3000 o C hard, unreactive (has protective oxide coating) and attractive. So used for chromium-plating and in making stainless steel titanium and its alloys are light but as strong as steel so used in aircraft construction hard brittle metal used to harden steel a strong metal that resists corrosion. Used in stainless steel and in coinage metals like cupronickel which has an attractive silvery appearance a grey metal with a blue tinge. Main use is to galvanise iron to prevent it from rusting unreactive metal and malleable. So used for making water-pipes Advantages Since transition elements speed up chemical processes in industries, they saves time in

10 manufacture Less energy is needed for manufacture in industries, hence lower cost Since less energy is needed, more energy resources can be conserved, e.g. oil to generate electricity in producing iron. MCQ 1. Which property decides the order of the elements in the Periodic Table? a. masses of their atoms b. number of electrons in the outer shell c. number of neutrons in the nucleus d. number of protons in the nucleus 2. The element with a proton number 12 has similar chemical properties to the element with the proton number a. 2 b. 11 c. 13 d Which element is in Group IV, Period 5 of the Periodic Table? a. antimony b. arsenic c. lead d. tin 4. Which statement about a new element, which has seven outer electrons in its atoms, is correct? a. it is monatomic b. it forms a covalent compound with hydrogen c. it forms a positive ion d. it forms covalent compounds with Group I elements 5. Which list contains 3 elements that all exist as diatomic molecules at room temperature? a. hydrogen, fluorine, neon b. nitrogen, chlorine, neon c nitrogen, oxygen, fluorine d. oxygen, chlorine, helium 6. Which statement shows that iron is a transition metal? a. Iron(II) sulphate crystals are green b. Iron(III) oxide is basic c. Iron rusts in moist air

11 d. Iron reacts with dilute hydrochloric acid 7. A metal X forms oxides with the formulae XO and X 2 O 3 Where is X in the Periodic Table? a. Group II b. Group III c. second Period d. transition elements 8. Which of the following is a property of aqueous potassium iodide? a. it does not conduct electricity b. it is decolorised by chlorine c. it reacts with aqueous bromine to form iodine d. it reacts with aqueous lead(ii) nitrate to form a white precipitate 9. Many properties of an element can its compounds can be predicted from the position of the element in the Periodic Table. What property could not be predicted in this way? a. acidic or basic nature of its oxide b. formula of its oxide c. number of isotopes it has d. its metallic or non-metallic properties 10. The element with a proton number 12 has similar chemical properties to the element with the proton number a. 2 b. 11 c. 13 d The proton number of Indium, In, is 49. What is the most likely formula for the oxide of Indium? a. In 2 O b. In 2 O 3 c. InO d. InO The element with proton number 12 has similar chemical properties to the element with the proton number a. 2 b. 11 c. 13 d Which statement about groups in the Periodic Table is correct? a. All groups contain both metals and non-metals.

12 b. Atoms of elements in the same group have the same total number of electrons. c. In Group I, reactivity decreases with increasing proton number. d. In Group VII, the melting point of the elements increases with proton number. 14. Which property decides the order of elements in the Periodic Table? a. masses of their atoms b. number of electrons in the outer shell c. number of neutrons in the nucleus d. number of protons in the nucleus 15. An element X, necessary for plant growth, can be added to the soil only in the form of compounds which contain the ion X. What is X? a. hydrogen b. nitrogen c. phosphorus d. potassium 16. The element Cs is in the same group of the Periodic Table as sodium and potassium. Which of the following is likely to be a property of caesium? a. It does not conduct electricity. b. It reacts vigorously with water to give off hydrogen. c. It forms the ionic chloride with formula CsCl 2 d. It forms an acidic oxide. 17. Which statement is most likely to be true about the elements in Group I of the Periodic Table? a. They occur uncombined in nature. b. They are equally reactive chemically. c. They form chlorides of similr fornulae. d. They become less metallic as the proton number increases. 18. Astatine (At) is in Group VII of the Periodic Table. Which of the following is a property of astatine? a. It forms a basic oxide. b. It is a good conductor of electricity. c. It is displaced by chlorine from aqueous potassium astatide. d. It displaces iodine from aqueous potassium iodide. 19. Which statement about a new element, which has seven outermost electrons in its atoms, is correct? a. It is monatomic. b. It forms a covalent compound with hydrogen. c. It forms a positive ion. d. It forms covalent compounds with Group I elements.

13 20. Fluorine is the first element in Group VII of the Periodic Table. Which statement will not be true of fluorine? a. Fluorine exists in diatomic molecules. b. Fluorine forms negative ions. c. Fluorine is less reactive than chlorine. d. Silver fluoride will be sensitive to light. Answers 1. d 2. d 3. d 4. b 5. c 6. a 7. d 8. c 9. c 10. d 11. b 12. d (Mg and Ca are in the same group in the Periodic Table) 13. d 14. d 15. d (Group I metals donate 1 outermost electrons to form X + ions) 16. b 17. c 18. c (Chlorine, being more reactive than At, displaces At from its aqueous salt) 19. b 20. c Worked Solutions 1. The elements below are all in Group I of the periodic Table. element symbol electronic structure lithium Li 2, 1 sodium Na 2, 8, 1 potassium K 2, 8, 8, 1 rubidium Rb 2, 8, 18, 8, 1 caesium Cs 2, 8, 18, 18, 8, 1 a. Which element reacts most vigorously with cold water?

14 b. Write the formula of a caesium ion c. How many protons are there in a rubidium ion? d. Group I elements are very good conductors of electricity. Use a simple model of the structure and bonding of the metal to explain this. Solutions a. Caesium b. Cs + c. 37 d. Metal consists of a lattice of cations in a sea of delocalised electrons. When a potential difference is applied across the metal, the electrons flow towards the positive potential, thereby conducting electricity. 2. This question is concerned with the following list of substances. potassium zinc oxide lead(ii) bromide hydrogen oxygen carbon Each substance can be used once, more than once, or not at all. Name a substance from the list above which a. reacts violently with water b. conducts electricity when molten but not when solid c. is amphoteric d. has a formula of the type XY2 e. has an allotrope with a structure similar to that of silica f. has a low melting point

15 g. is produced at the cathode during electrolysis of dilute sulphuric acid Solutions a. potassium b. lead(ii) bromide c. zinc oxide d. lead(ii) bromide e. carbon f. oxygen g. hydrogen 3. Chlorine, bromine, and iodine are elements in Group VII of the Periodic Table. a. Describe how you would carry out a series of experiments to show the trend in reactivity of these three elements, using the reagents below. aqueous chlorine aqueous bromine aqueous iodine aqueous potassium chloride aqueous potassium bromide aqueous potassium iodide Your answer should include details of: - which of the reagents you would use in each experiment - a table showing the observations you would expect to see - the equations for any reactions b. Chlorine reacts with water to make a solution that can be used as a bleach. The equation is show below Cl2 + H2O ---> HCl + ClOH Use oxidation numbers to show that chlorine is both oxidised and reduced in this reaction. Solution 3a. A more reactive halogen would displace a less reactive halogen from its salt solution. Displacement reactions are carried out to investigate the trend of reactivity of the halogens.

16 Add a few drops of chlorine water into a test tube containing 2cm 3 of potassium chloride solution. Record changes observed. The experiment is repeated with potassium bromide and potassium iodide solution. To find out the order of reactivity of the halogens, a second set of experiments is conducted with bromine water added to test tubes containing 2cm 3 of each of the salt solution provided and a third set of experiments conducted with iodine solution added to 2cm 3 of each of the salt solution. The results are shown below: Halogen added KCl KBr KI Cl 2 (aq) - Colourless solution turned Colourless solution turned brown. Br2 formed reddish brown. I2 formed Br 2 (aq) No displacement reaction - Colourless solution turned reddish brown. I2 formed I 2 (aq) No displacement reaction No displacement reaction - Equations: Cl2 + 2KBr ---> 2KCl + Br2 Cl2 + 2KI ---> 2KCl + I2 Br2 + 2KI ---> 2KBr + I 2 3b. Chlorine is oxidised to ClOH and reduced to HCl at the same time. In the oxidation process, oxidation number of chlorine increased from 0 in Cl 2 to +1 in ClOH. In the reduction process, oxidation number of chlorine decreased from 0 in Cl 2 to -1 in HCl. 4a. The reaction of aluminium chloride with water is as follows: 2AlCl 3 + 6H 2 O ---> 2Al(OH) 3 + 6HCl Each of the following compounds aluminium bromide (AlBr 3 ) aluminium nitride (AlN) aluminium carbide (Al 4 Cl 3 ) reacts with water in a similar way. Predict the formula of the compound produced, other than aluminium hydroxide in each case. b. NaNO 3 NH 3 CuSO 4 MgCO 3 Al 2 O 3 Choose from the above list of compounds one which contains:

17 i. an element found in Group II of the periodic table ii. a metallic element showing an oxidation number of +3 iii. a non-metallic element showing an oxidation number of -3 iv. a non-metallic element showing an oxidation number of +5 Solution 4a. aluminium bromide: HBr produced aluminium nitride: NH 3 produced aluminium carbide: CH 4 produced 4bi. MgCO 3 4bii. Al 2 O 3 4biii. NH 3 4biv. NaNO 3 5. The Periodic Table is arranged in groups. a. Rubidium (Rb) is in Group I of the Periodic Table. It reacts with water according to the equation below 2Rb (s) + 2H 2 O (l) --> 2RbOH (aq) + H 2 (g) Predict what you would see when a small piece of rubidium is added to cold water. b. Chlorine is in Group VII of the Periodic Table. Chlorine, Cl 2, reacts with aqueous sodium bromide. i. Predict what you would see in this reaction. ii. Write a balanced equation for this reaction. Solution 5a. Rubidium will react violently with cold water. It melts into a silvery ball, effervesces and releases a lot of heat and light energy. 5bi. The colourless solution of sodium bromide will react with the yellowish green chlorine gas to form a solution that is reddish brown in colour. 5bii. Cl 2 + 2Br - --> 2Cl - + Br 2 6. Chlorine, bromine and iodine are elements in Group VII of the Periodic Table. a. Describe the trend in colour and physical state at room temperature and pressure as the atomic number increases. b. Aqueous chlorine is an oxiding agent. i. Name the products formed and write the ionic equation for the reaction between aqueous chlorine and aqueous potassium bromide. ii. Name the product formed when aqueous chlorine reacts with aqueous iron(ii) chloride. Solution

18 6a. As atomic number increases down the group, the physical states change from gas (fluorine and chlorine) to liquid (bromine) and then to solid (iodine, astatine). The colour intensity also increases from pale yellow (fluorine) to yellowish green (chlorine) and then to red-brown (bromine) and finally to black (iodine and astatine). 6bi. Chloride and bromine. 2Br - + Cl 2 --> 2Cl - + Br 2 6bii. iron(iii) chloride