THE ST. MICHAEL SCHOOL THIRD FORM CHEMISTRY MANUAL

Transcription

1 1 THE ST. MICHAEL SCHOOL THIRD FORM CHEMISTRY MANUAL PERIODIC TABLE, METALS AND NON METALS Compiled by G, Walker, T. Harding, C.L. Worrell REFERENCE BOOKS Chung-Harris, Taylor Chemistry for CSEC Earl, Wilford, Chemistry for CSEC examination Hill Science for GCSE Potter, Oliver Integrated Science for CXC Coordinated Science Chemistry

2 2 PERIODIC TABLE WHAT IS THE PERIODIC TABLE The periodic table is an arrangement of the elements based on their atomic number. The horizontal rows are PERIODS The vertical columns are GROUPS GROUPS There are eight groups numbered I to VII and then group 0. The group number refers to the number of electrons in the outer shell of the atom (valence electrons) The members of a group differ in the number of inner shells of electrons. The members of a group have the same number of electrons in their outer shells. Elements in a group have similar chemical properties, i.e. they react similarly, this is because they have the same number of electrons in their outer shells. REACTIVITY IN GROUPS The reactivity increases down groups (I, II, III) since the outer most electrons are farther away from the attractive pull of the nucleus. The reactivity increases up group IV, V, VI AND VII since the electrons become progressively closer to the pull of the positive nucleus. CHANGES IN SIZE The atomic size increases down a group since one shell is added as you go down a group.

3 GROUP 1 THE ALKALI METALS These are lithium, sodium, potassium, rubidium, Caesium, Francium They are shiny when freshly cut. They react with oxygen to form a dull layer of oxide. They react with water to form alkaline solutions. They are very reactive and soft. They have low densities compared to other metals and float on water. The reactivity of the group one and two elements increases down the group. GROUP 2 THE ALKALINE EARTH METALS These include beryllium, magnesium, calcium, strontium and barium. They form alkaline suspensions in water. They are often found in rocks as minerals e.g. limestone and gypsum. They can lose their outer electrons to form cations. The farther away the outer shell is from the nucleus, the easier it is for the atom to lose the outer electrons. For this reason reactivity increases down the group. TRANSITION METALS These are found between groups II and III. They can have several valencies and thus form two or more ions with different charges.. They form coloured compounds e.g. copper sulphate is blue; iron compounds are green or brown. They have high melting points and boiling points. They have high densities. They are hard, strong metals. They are denser than the alkali metals. Many of them are catalysts (speed up the rate of a reaction). GROUP 7 HALOGENS Halogens include fluorine, chlorine, bromine and iodine. They are all diatomic that is they form molecules with two atoms F 2, Cl 2, Br 2 and I 2. The form negative ions, i.e. they gain electrons. The reactivity of halogens decreases down the table. This is because as the outer shell becomes further away from nucleus, It becomes more difficult for the positive nucleus to draw away electrons from other atoms. GROUP 0 NOBLE GASES Group 0 or 8 are called the NOBLE GASES. They have complete outer shells this makes them very stable and for this reason they are very unreactive. All noble gases exist as separate single atoms. Noble gases have a variety of uses: He in weather balloons, Ne in advertising lights, Ar in welding. PERIODS There are seven periods numbered 1 to 7. All elements in a period have the same number of shells. Going across a period each element has one more proton and one more electron than the previous element. Element become less metallic and more non-metallic as you go across a period. Group I metals are more reactive than group II metals because the it requires less energy to remove one electron than two. QUESTIONS 1. (a) Here is a list of the symbols of the first ten elements of the Periodic Table. They are in the wrong order. Re-write the list in the correct order, starting with hydrogen (H). He H F Ne O N C Be B Li (b) Chlorine, bromine and iodine are part of Group VII of the Periodic table. Explain what is meant by a Group of the Periodic Table. Explain what is meant by a Period of the Periodic Table. 2. Use your knowledge of atomic structure to explain the following: (a) Why atoms of elements low down a Group of the Periodic Table are larger than those at the top of the Group. (b) Why atoms of elements near the right-handed side of a period in the Periodic Table are smaller than those near the left-handed side.

4 4 3. Part of the periodic table is shown below. Use the information to help you answer the questions which follow. (a) Write the symbol for: (i) chlorine (ii) sodium (b) (i)what is the symbol of the element which is in group 2 and period 3? (ii) What name is given to group 7? (c) The arrangement of electrons for (i) neon (Ne); (ii) aluminium. (d) The periodic table is an arrangement of elements in order of increasing atomic number. What is the atomic number of an element? (e) What is the name of the uncharged particle in the nucleus of an atom? VALENCY AND CHARGES The valence electrons are the electrons in the outer shell. If an atom looses electrons it becomes positively charged a cation. If an atom gains electrons it becomes negatively charged an anion. The table below shows the valencies and charges of some elements are radicals. Radicals are Groups of atoms which are bonded together and do not separate during a reaction. Valency Table Valency of 1 Elements Hydrogen H Lithium Li Potassium K Fluorine F Chlorine Cl Bromine Br Iodine I Valency of 2 Beryllium Be Magnesium Mg Calcium Ca Oxygen O Sulphur S Barium Ba Copper (II) Cu Iron (II) Fe Lead (II) Pb Nickel Ni Zinc Zn Valency of 3 Boron B Aluminium Al Nitrogen N Phosphorus P Iron (III) Fe Binary compounds of nitrogen are called nitrides. Valency of 4 Carbon C Silicon Si Lead (IV) Pb TABLE SHOWING CHARGES CARRIED BY COMMON ANIONS, CATIONS AND RADICALS ANIONS + CHARGE NEG- ATIVE Phosphate RADI- PO42- Nitride N3- CALS CATIONS + POSI- TIVE RADI- CALS Chloride, Cl- Bromide Br- Iodide I- Fluoride F- Hydroxide OH- Manganate (VII) MNO4- Hydrogencarbonate HCO3- Ethanoate CH3COO- Methanoate HCOO- Hydrogen sulphate HSO4- Sulphate SO42- Sulphite SO32- Carbonate CO32- Oxide O2- Suphide S2- Chromate (VI) CrO42- Dichromate (VI) Cr2O72- Ethanediote C2O42- CHARGE Metals of Group 1: Li+, Na+, K+ Metals of Group 2 Hydride H+ Ammonium NH4+ Silver Ag+ Copper (I) Cu+ Metals of group II: Mg2+, Ca2+, Ba2+ Lead (II) Pb2+ Iron (II) Fe2+ Zinc Zn2+ Tin(II), Sn2+ Copper (II) Cu2+ Aluminium Al3+ Iron (III) Fe3+ Chromium(III) Cr3+

5 5 QUESTIONS Copy and complete the following statements. 1. The periodic table lists elements according to increasing 2. For the first twenty elements there are groups and.periods. 3. A Group is 4. A Period is. 5. The elements in a period all have the same.. 6. Elements in Groups 1 3 are..and elements in Groups 4-7 are. 7. Group 0 or 8 elements are called 8. Group 1 elements are called.. 9. Group 2 elements are called The Halogens is the name given to the family of elements in. 11. The atomic number of lithium, sodium and potassium is,,and The electron configuration of lithium, sodium and potassium is., and 13. In any group the size of the atom (increases/decreases) as you go down the group. This is so since

6 6 14. The electrons in the outermost shell of an atom are called. 15. The elements in a group all have the same number of 23. The electron configuration of the first three elements in group 2 is., and.. 24.As you go down a group 1 reactivity (increases/decreases). This is so since 16. As a result of the answer in Q15. the elements in a group have similar. 17. The noble gases are generally unreactive since. 18. The halogens all exist as..molecules and all have.vapours. 25. As you go down a group 1 melting points and boiling points (increase/decrease). This is so since 26. Group 1 elements are more/less reactive than Group 2 elements since As you go up group 7 the elements get(more / less ) reactive since the outershell electrons are( closer / farther ) to/from the attractive pull of the.. positively charged nucleus. 27. Group 7 elements are more/less reactive than Group 6 elements 20. In what states do the elements in group 7 exist at room temperature? since Fluorine is a..chlorine is a Bromine is a Iodine is a List four properties of transition metals i). 21. Why are the elements in group 7 reactive? List the first three elements in group 2. ii) iii) iv) 29. Look at a copy of the periodic table and write the names and symbols

7 of four transition metals. 30. Astatine is in the same group as chlorine. Would you expect astatine to be more or less reactive than chlorine. Explain. Here are some examples. Sodium has three shells and one electron in the outer shell. Since 1 < 3 sodium is a metal Barium is in the same group as calcium. Would you expect barium to be Sulphur has three shells and 6 electrons in the outer shell. more or less Since 6 > 3, sulphur is a non metal. Draw a line on your periodic table separating metals from non metals. reactive than calcium. Explain Would you expect Aluminium to be more or les reactive than Magnesium. Explain... 7 METALS AND NON METALS IDENTIFYING METALS AND NON METALS IN THE PERIODIC TABLE Metals have an equal or few number of electrons in their outer shells than shells. Non metals have more electrons in their outer shells than shells. Calcium has four shells and two electrons in the outer shell. Since 2 < 4 calcium is a metal PROPERTIES OF METALS AND NON-METALS Table showing the properties of metals and non-metals Most non-metals Most metals Solids have a high melting points, giving high boiling point liquids Shiny, reflecting light Gases or low melting point solids giving low boiling point liquids Dull, reflecting light poorly or absorbing strongly High density Low density Usually hard Usually soft Malleable, ductile, strong Often brittle, weak Good conductors of heat and Insulators electricity Malleable easily hammered into shape

8 8 Ductile can be drawn into wires. Material Use Reason Metal Electrical appliances Cooking implements Gardening and other tools, Furniture, nails, doors and gates Wood Plastic Furniture Handles Food containers, pipes, tooth Brushes, hangers, outside of electrical fittings and wires. They conduct electricity The conduct heat They are strong and malleable. REACTIVITY OF METALS The following shows the reactivity of selected metals Na Mg Al Zn Fe Sn (Tin) Cu (copper) Ag (silver) most reactive decreasing reactivity least reactive They are insulators, less dense than metal (density does vary with type of wood) Plastics are light, insulators, easy to mould into a variety of shapes REACTIVITY OF METALS WITH ACID AND WATER Metal sodium Magnesium Aluminium Zinc Iron Reacts with: Water/steam Violent with cold water forms hydrogen and sodium hydroxide solution Very slow with cold water but vigorous with steam No reaction, protected by oxide layer Reacts with steam, giving hydrogen Rust with water, forms hydrogen with steam Acid Vigorous, forms hydrogen and magnesium chlorine solution. Effervescence, forming hydrogen and a salt. Effervescence, forming hydrogen and a salt. Effervescence, forming hydrogen and a salt. Tin No reaction Slow reaction forming hydrogen and a salt Copper No reaction No reaction Silver No reaction No reaction RUSTING Rusting is the formation of hydrated iron oxide in the presence of oxygen and moisture. Iron + oxygen (in the presence of moisture) rust Salt in sea water can make iron rust more quickly as well as the acid in acid rain. Rusting can be prevented by preventing moisture from coming into contact with the metal. This can be done with: painting, galvanizing (coating object with zinc), tin-plating, oiling, electroplating (covering iron with another metal), plastic coating and sacrificial protection (e.g. magnesium is attached to the side of a steel ship, it corrodes

9 9 instead of the steel. When it is nearly eaten away it can be replaced the magnesium is sacrificed to protect the steel. Removing Rust Stains Rust stains can be removed with acids such as lemon juice. Implications of Rusting in the Caribbean Since the islands of the Caribbean are surrounded by sea water and experience sea breezes daily, rusting is a real and expensive problem. It affects vehicles and equipment. Money is spent preventing rusting and replacing rusted items. QUESTIONS 1. Suggest reasons why: (a) Silver is used for jewellery; (b) Mercury is used in thermometers (c) Aluminium is used for beer cans. 2. Compare how aluminium and iron each react with oxygen. 3. Which is more reactive, zinc or tin? 4. Explain why tin is used to coat food tins. 5. What gas is always produced it a metal reacts with water? 6. What two substances cause rusting? 7. Steel that is tin-plated does not rust. Why?

10 (a) (b) (c) What are alloys? How are they made? Which metals are used to make: stainless steel? Duralium? Bronze? Name an allow that never rusts.