8.3. Group VII properties
A subsection of Chemistry, 0620, through 8. The Periodic Table
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The table below shows the properties of some halogens. halogen colour state at room temperature melting point / °C fl uorine yellow –220 chlorine light green gas bromine brownish-red liquid –7 iodine grey-black solid +114 What is the trend in the colour of the halogens down the Group? Predict the state of fl uorine at room temperature. Predict the melting point of chlorine. The reactivity of three different halogens was compared by reacting them with solutions of sodium halides. The results are shown in the table below. reaction mixture observations astatine + sodium iodide colour of reaction mixture remains unchanged bromine + sodium iodide mixture turns dark brown chlorine + sodium bromide mixture turns brownish-red Use the results in the table to suggest the order of reactivity of astatine, bromine, chlorine and iodine. most reactive least reactive Predict whether bromine will react with sodium chloride solution. Explain your answer. Chlorine reacts with excess cold dilute sodium hydroxide. The products of the reaction are sodium chloride, sodium chlorate(and water. The formula of sodium chlorate(is NaCl O. Complete the equation for this reaction. Cl 2 + NaOH → NaCl + NaCl O + Explain why chlorine is used in water purifi cation. Impure water contains particles of minerals and remains of dead plants and animals. One stage in water purifi cation is the removal of these particles by fi ltration. The diagram below shows a water fi lter. water in small particles of sand Explain how this water fi lter works.
0620_w12_qp_22
THEORY
2012
Paper 2, Variant 2
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Three of the halogens in Group VII are listed below. chlorine bromine iodine How does their colour change down the Group? How do their melting points and boiling points change down the Group? Predict the colour and physical state (solid, liquid or gas) of astatine, At. colour physical state A radioactive isotope of iodine, I 131 , is used to treat cancer. Defi ne the term isotope. How many protons, electrons and neutrons are there in one atom of I 131 ? number of protons number of electrons number of neutrons When this isotope, I 131 , emits radiation, a different element with a proton number of 54 is formed. What is the name of this element? Fluorine, the most reactive halogen, forms compounds with the other halogens. It forms two compounds with bromine. Deduce their formulae from the following information. compound 1 The mass of one mole of this compound is 137 g. Its formula is compound 2 0.02 moles of this compound contain 0.02 moles of bromine atoms and 0.1 moles of fl uorine atoms. Its formula is
0620_w12_qp_31
THEORY
2012
Paper 3, Variant 1
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The halogens are a collection of diatomic non-metals in Group VII. Defi ne the term diatomic. What do the electron distributions of the halogens have in common? How do their electron distributions differ? Complete the table. halogen solid, liquid or gas at room temperature colour chlorine bromine iodine The halogens react with other non-metals to form covalent compounds. Draw a diagram which shows the arrangement of the valency electrons in one molecule of the covalent compound arsenic trifl uoride. The electron distribution of an arsenic atom is 2 + 8 + 18 + 5. Use x to represent an electron from an arsenic atom. Use o to represent an electron from a fl uorine atom. Photochromic glass is used in sunglasses. In bright light, the glass darkens reducing the amount of light reaching the eye. When the light is less bright, the glass becomes colourless increasing the amount of light reaching the eye. Photochromic glass contains very small amounts of the halides silver(chloride and copper(chloride. The reaction between these two chlorides is photochemical. AgCl + CuCl Ag + CuCl 2 colourless colourless black colourless How does photochromic glass work?
0620_w13_qp_32
THEORY
2013
Paper 3, Variant 2
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A student placed a crystal of iodine in a test tube of solvent. After two minutes, a dense violet colour was observed at the bottom of the test-tube. After three hours, the violet colour had spread throughout the solvent. at the start after 2 minutes after 3 hours solvent Use the kinetic particle theory to explain these observations. In your answer, refer to: ● the arrangement and motion of the molecules in the iodine crystal, ● the arrangement and motion of the molecules in the solution, ● the names of the processes which are occurring. Astatine, At, is below iodine in Group VII of the Periodic Table. The table shows the states of the Group VII elements at room temperature. element state fl uorine gas chlorine gas bromine liquid iodine solid Use this information to deduce the state of astatine at room temperature. Astatine is radioactive. A lot of heat is given off due to this radioactivity. The small samples of astatine that have been isolated are often liquid. Suggest why they are often liquid. Although few compounds of astatine have been made, scientists think that sodium astatide will react with iodine. Complete the equation for this reaction. I2 + NaAt → 2NaI +
0620_w14_qp_21
THEORY
2014
Paper 2, Variant 1
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Describe the properties of chlorine, bromine and iodine. In your answer, include the trends in: ● their state, ● their colour, ● their reactivity. A molecule of chlorine can be written as Cl – Cl. Which one of the following words describes this molecule? Put a ring around the correct answer. diatomic giant ionic monatomic Draw the electronic structure of a fl uorine atom. The equation below describes the reaction of a halogen with a halide. Br2 + 2KI → I2 + 2KBr Write a word equation for this reaction.
0620_w14_qp_23
THEORY
2014
Paper 2, Variant 3
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Chlorine is in Group VII of the Periodic Table. One isotope of a chlorine atom has a nucleon number of 35. Describe the structure of an atom of this isotope of chlorine. In your answer refer to • the type and number of each subatomic particle present, • the charges on each type of subatomic particle, • the position of each type of subatomic particle in the atom. Chlorine reacts with sodium to form sodium chloride. Sodium chloride contains Na+ ions and Cl – ions. Explain why sodium ions are positively charged and chloride ions are negatively charged. When chlorine reacts with aqueous potassium iodide, the solution turns brown. Suggest why the solution turns brown. Explain why aqueous potassium chloride does not react with iodine. The structure of a chlorofluorocarbon is shown below. C F F F F Cl F C Deduce the molecular formula of this compound.
0620_w15_qp_23
THEORY
2015
Paper 2, Variant 3
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Questions Discovered
123