4 THE PERIODIC TABLE
ASSIGNMENT 3: EXPLAINING RADII A5. Write the full electron configurations for:
(MS 3.1; PS 1.1, 1.2, 2.3, 3.2) Table A1 lists values for the atomic and ionic radii of some elements. The ionic radius measures the radius of an ion. For example, a sodium ion, Na+, has a radius of 0.098Â nm.
Element
Atomic radius/nm
Ionic radius/nm
lithium
0.152
0.078
sodium
0.186
0.098
magnesium
0.160
0.078
oxygen
0.073
0.124
fluorine
0.071
0.133
Table A1
You are going to use the ideas you have learnt about periodicity to explain some trends in atomic and ionic radii.
Questions A1. Write the symbols for all the ions in Table A1.
a. a sodium ion b. a magnesium ion. A6. Explain why a magnesium ion is smaller than a sodium ion. A7. Write the full electron configuration for: a. a fluoride ion b. an oxide ion. A8. Explain why both fluoride and oxide ions are larger than their respective atoms. A9. Positive ions are cations, negative ions are anions. Suggest how atomic radius compares to the ionic radius of: a. cations b. anions. A10. Use data from Figure 5 to answer these questions. a. What is the atomic radius, in metres, of the elements from sodium to argon? Show your answer in standard form.
A2. Explain why a sodium atom has a larger radius than a lithium atom.
b. Draw a dot-to-dot line graph of atomic number against atomic radius (nm) for the elements sodium to argon.
A3. Explain why a sodium atom has a larger radius than a magnesium atom.
c. Annotate your graph to explain the trend.
A4. Explain why a lithium ion is smaller than a lithium atom.
PRACTICE QUESTIONS 1. The elements in Period 2 show periodic trends. a. Identify the Period 2 element, from carbon to fluorine, that has the largest atomic radius. Explain your answer. b. State the general trend in first ionisation energies from carbon to neon. Deduce the element that deviates from this trend and explain why this element deviates from the trend.
c. Write an equation, including state symbols, for the reaction that occurs when the first ionisation energy of carbon is measured. d. Explain why the second ionisation energy of carbon is higher than the first ionisation energy of carbon. e. Deduce the element in Period 2, from lithium to neon, that has the highest second ionisation energy. AQA Jun 2013 Unit 1 Question 6
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