Periodicity

Question 1

What are the uses of chlorine?

Answer 1

-swimming pools
-bleaches
-water purification

Question 2

How does chlorine react with water?

Answer 2

-forms HCl and HClO
-reaction occurs to purify water and swimming pools
-disproportionation reaction

Question 3

What is a disproportionation reaction?

Answer 3

-when the oxidation number of an elements atom change differently throughout the reaction as one increases and one decreases

Question 4

How does chlorine purify water?

Answer 4

-produces chloric acid which is an oxidising agent and kills bacteria via oxidation and is used as a bleach

Question 5

How is the reaction of chlorine different in sunlight?

Answer 5

produces HCl and O2
-chlorine is rapidly lost

Question 6

Reaction of sodium chlorate and water

Answer 6

-dissolves in water to form HClO
-equilibrium moves to left in alkaline solutions which is reason why swimming pools are kept acidic

Question 7

Reaction of chlorine with NaOH

Answer 7

-cold and dilute forms sodium chlorate NaClO which is an oxidising agent used in bleach
Disproportional reaction.

Question 8

Describe and explain the melting points of the group 2 elemements?

Answer 8

-decrease going down the group
-atomic radius increases so the delocalised electrons are further from the nucleus so metallic bonds are weaker
-Mg does not fit this pattern

Question 9

Describe and explain the trends in ionisation energies of the the group 2 elements

Answer 9

-decrease both 1st and 2nd as atomic radius increases and so does electron shielding
-means that there is smaller electrostatic force so energy to remove outer electron decreases
-electronegativity also decreases

Question 10

Describe the relative solubility of hydroxides

Answer 10

-all form white solids and become more soluble going down the group
-MgOH is least soluble and is sold as a suspension in water as milk of magnesia
-barium hydroxide is very soluble and is dissolved to produce very alkaline solution

Question 11

Describe the relative solubilities of sulfates in group 2

Answer 11

-less soluble going down the group
-barium sulfate is virtually insoluble

Question 12

Describe group 2 reaction with water

Answer 12

-more reactive going down the group
-magnesium reacts slow with water but rapidly with steam to form alkaline oxide and hydrogen
-Ca reacts more vigorously which increases down the group

Question 13

Describe the process of which Ti is extracted

Answer 13

-Ti is a strong low density metal with a high melting point so is used in aerospace engineering
-cannot be reacted with carbon to be extracted as Titanium carbide forms making the metal brittle so Ti oxide reacts with chlorine and carbon to form TiCl which is then reduced to Ti by reacting with Mg

Question 14

Describe the practical uses of group 2

Answer 14

-barium sulfate can be used as a medical tracer and is given via mouth. It is toxic if enters the bloodstream but it is insoluble so will only cause small side effects
-highlights problems with digestive tract finding ulcers and tumours via appearing white on the xray

-magnesium hydroxide are used in indigestion tablets as an antiacid as it neutralises a strong acid and as it is insoluble it only reacts in stomach

-calcium hydroxide used a a slake lime to neutralise acidic soils replacing H ions making it more suitable for plant growth

Question 15

Group 7 physical properties

Answer 15

flourine - pale yellow gas
chlorine - greenish gas
bromine - dark red/brown liquid
iodine - black solid

become darker and denser going down the group

Question 16

Explain why fluorine has untypical physical characteristics

Answer 16

due to weaker F-F bonds causing a smaller size leading to repulsion between non-bonding electrons

Question 17

Explain the trends in electronegativity of group 7

Answer 17

-decreases going down the group as the atomic radius increases so outer electron is further from the nucleus
-increase in electron shielding overrides increasing positive charge

Question 18

Explain the trends in the melting and boiling points of group 7 elements

Answer 18

-increase going down the group as larger atoms have larger amounts of electrons so stronger vdw forces
-the lower the boiling point the more volatile an element is so fluorine is the most volatile

Question 19

Trends in the oxidising ability of the halogens

Answer 19

-usually gain electrons acting as the oxidising agent as they are reduced
-oxidising ability decreases going down the group so fluorine is the strongest oxidising agent due to its small atomic radi and small shielding
-reducing ability increases going down the group

Question 20

how do the halogens react with metal halides?

Answer 20

the halide in the compound will displaced by a more reactive halogen

Question 21

Explain the extraction of bromine from sea water

Answer 21

-oxidation of a halide by a halogen as sea water contains bromine ions that can be oxidised by chlorine

Question 22

Explain the extraction of iodine from kelp

Answer 22

-burn the seaweed and the heat the residue with managanseoxide and sulfuric acid

Question 23

State the reaction of sodium chloride with sulfuric acid

Answer 23

-hydrogen chloride and sodium hydrogen sulfate form
-not a redox reaction as no oxidation state has changed
-chloride ion is too weak of a reducing agent to reduce sulfur
-similar occurs with sodium fluoride and hydrogen fluoride gas forms

Question 24

State the reaction of sodium bromide with sulfuric acid

Answer 24

-hydrogen bromide, bromine, and colourless sulfur dioxide are formed via two reactions

1) sodium hydrogen sulfate and hydrogen bromide are produced
2) bromide ions are stronger reducing agents so reduce sulfuric acid to sulfur dioxide

-reaction is exothermic and some bromine vaporises

Question 25

Sodium iodide

Answer 25

-hydrogen iodide, iodine, hydrogen sulfide, yellow sulfur and sulfur dioxide -iodine ions reduce sulfuric acid further +6 to zero and -2 and yellow solid sulfur can be seen as it passes through oxidation states

Question 26

Describe period 3 elements properties

Answer 26

-in groups 1,2,3 they are metals so have giant structures and loose electrons to form ionic compounds -silicon in group 4 has 4 outer electrons so forms 4 covalent bonds and is classed as a semi-metal -group 5,6,7 are non-metals and can form ionic/covalent structures -group 8 is unreactive noble gases

Question 27

Describe the atomic radius across period 3

Answer 27

-decreases across the group -measured between the centres of 2 atoms -along the period means increased charge due to larger no. of protons in the nucleus -no difference in electron shielding -radius decreases

Question 28

Explain the pattern of the first ionisation energies of period 3

Answer 28

-no, of protons increases but shielding remains the same so the increasing positive charge makes it more difficult to move outer electron Exception- drops between group 2 and 3 between Mg and Al as Al has lower ionisation energy as its outer electron is in p-orbital which requires much less energy than s-orbital -drop between group 5 and 6 they are in the same orbital and have the same shielding but P has no paired electrons but S has one which makes it easier to remove as the electrons are experiencing repulsion

Question 29

Describe the melting points of period 3

Answer 29

-giant structures have higher mp -molecular and atomic structures have lower mp -from group 1 to 3 it increases as metallic bonds get stronger -Si is macromolecular so covalent bonds exist requiring energy to break -non-metals are dependent of their vdw forces and no. of electrons -Ar has low mp as it is monotomic so has weak vdw