Higher (National 6) Unit 1: Chemical changes and structure 1b Periodicity

Transcription

1 Higher (National 6) Unit 1: Chemical changes and structure 1b Periodicity 1. The graph below shows the melting points for the elements across a row in the Periodic Table. a) Identify the row represented by the graph b) A and B have metallic bonding. Explain why the melting point of B is higher than that of A. c) Elements D and E are both covalently bonded. In terms of the type of bonds and structure explain the large difference in melting points. d) What is the trend in the strength of the intermolecular forces between the elements F to H? Account for this trend. 2. Which type of bond is broken when silicon is melted? 3. (a) Identify the term which can be applied to lithium but not to carbon. (b) Identify the term(s) which can be applied to both fluorine and phosphorus. A Covalent B Metallic C Discrete molecules D Diatomic molecules E Gas E Solid 1

2 4. 5 distinct structures exist among the elements. These are: 1. closely packed molecules 2. giant covalent network structure 3. giant metallic lattice 4. atomic gas 5. molecular gas Which of these best describe the normal state of sulphur, boron, argon and aluminium? 5. a) What type of bonding would you predict between: i) Atoms of fluorine ii) Atoms of lithium b) Using atoms of fluorine as an example explain how the nuclei and shared electrons fomr this type of bond. 6. A Metallic structure B Monatomic gas C Network structure D Discrete molecule Choosing from the answers listed above, which box or boxes show(s) a substance that: a) is a non-conductor with a low melting point? b) conducts well and have a high melting point? c) is a non-conductor and has a very high melting point? d) could be: i) hydrogen ii) helium iii) zinc iv) silicon? 7. Name three forms of carbon and describe how they differ in both structure and properties from each other. 2

3 8. The table below shows the first 20 elements. They are in 5 groups A to E. a) Identify the group of elements that show the following structures: i) monatomic gases ii) covalent network iii) metallic iv) covalent molecular solids v) covalent molecular gases b) In which of the groups (A to E) are the following correct i) mobile electrons allow the elements to conduct when solid ii) both covalent and London Dispersion Forces are present iii) only covalent bonds are present iv) only London Dispersion Forces are present. 9. a) Describe and explain the change in the covalent radius from lithium to fluorine. b) Why does the covalent radius increase from lithium to caesium? 10. Explain the difference in size between a: a) Na atom and an Na + ion b) Na + ion and a F - ion c) Si 4+ ion and the N 3- ion. 3

4 11. The Na + ion and the Mg 2+ ion have the same electron arrangement. Why is the magnesium ion smaller than the sodium ion? 12. a) Write the equation for the first ionisation energy of lithium. b) The ionisation energy decreases going down a group, e.g. Li to Cs, give a reason for this trend. c) On crossing a row in the Periodic Table there is a change in the ionisation energy. State the change and give an explanation. 13. Why is there no value given in the data booklet for the fourth ionisation energy of lithium? 14. Na (g) --> Na + (g) + e - Na + (g) --> Na 2+ (g) + e - H = A H = B a) Use your data booklet to obtain the values for A and B. b) Calculate the total energy required for the energy change shown: c) Explain why the second ionisation energy of sodium is so much greater than the first. 15. Write the equation to represent the second ionisation energy of copper. 16. The difference between the covalent radius of sodium and silicon is mainly due to the difference in the: A B C D number of electrons number of protons number of neutrons mass of each atom 4

5 17. The diagram shows the first ionisation energies of successive elements A to T, plotted against their atomic numbers. a) Which group of elements is represented by the letters: i) I and Q ii) C, K and S b) Why is the first ionisation energy of element L greater than that of K? c) Why is the second ionisation energy of element L considerably less than that of element K? 18. The covalent radius of technetium, atomic number 43, is not known. a) How would you expect the covalent radius of technetium to compare with that of: i) manganese ii) cadmium (atomic number 48)? b) Explain your answer to a) i). 19. a) Why is the first ionisation energy of each alkali metal much less than that of the halogen in the same period? b) why is the second ionisation energy of each alkali metal much greater than that that of the halogen in the same period? c) Calculate the energy per mole required to bring about the change: K + (g) --> K 3+ (g) + 2e - 5

6 20. a) What is meant by the electronegativty of an element? b) In the Periodic Table what is the trend in electronegativity on i) crossing a row ii) going down a group Explain the trend in each of the above scenarios. 6

7 Exam type questions ( )

8 Information about four elements from the third period of the Periodic Table is shown in the table. a) Complete the table to show the bonding and structure for each element. b) What feature of the bonding in aluminium allows it to conduct electricity? c) Why is there a decrease in the size of atoms across the period from aluminium to sulphur? 8

9 14. Attempts have been made to make foods healthier by using alternatives to traditional cooking ingredients. a) An alternative to common salt contains potassium ions and chloride ions. Write an ion-electron equation for the first ionisation energy of potassium. b) Explain clearly why the first ionisation energy of potassium is smaller than that of chlorine. 15. The elements lithium to neon make up the second period of the Periodic Table. a) Name an element from the second period that exists as a covalent network. b) Why do the atoms decrease in size from lithium to neon? 16. The elements from sodium to argon make up the third period of the Periodic Table. a) On crossing the third period from left to right there is a general increase in the first ionisation energy of the elements. i) Why does the first ionisation energy increase across the period? ii) Write an equation corresponding to the first ionisation energy of chlorine. b) The electronegativities of elements in the third period are listed on page 10 of the data booklet. Why is no value provided for the noble gas, argon? 9

10 Unit 1: Chemical changes and structure Periodicity Ink exercise 1. The following table shows the five different types of structure that exist among the first 20 elements of the periodic table: A molecular gas B molecular solid C atomic gas D covalent network E positive ions in a sea of electrons Which structure best describes the state of the following elements at room temperature. a) fluorine b) sodium c) sulphur d) neon e) silicon [2] 2. Use the Data book to answer the following questions a) Name the element with the lowest first ionisation energy. b) Explain why this element has the lowest ionisation energy. c) State the third ionisation energy of magnesium and aluminium. d) Explain why magnesium has a far higher third ionisation energy [4] 3. Explain why: a) the sodium atom is larger than the chlorine atom. b) atoms get larger going down a group in the Periodic Table c) the fluoride ion (F - ) is larger than the sodium ion (Na + ) [3] 3. Use information in the Data book to explain why electronegativity can be described as a periodic property (Hint: for 2 marks you would be expected to comment on the trend across a period and down a group). [2] 4. The graph below shows the first ionisation energies of successive elements A to T, plotted against their atomic numbers. a) Which group of elements is represented by B, J and R? 10

11 Question 4 continued b) State which elements can be identified as (i) (ii) halogens alkali metals c) Identify the letter of an element in Period 2 that does not fit the pattern. [4] [/15] 11