Group 2 And Group 7 Elements Flashcards
What do group 2 elements do to react?
Lose their outer two electrons to form 2+ ions. Their ions then have the structure of a noble gas
What happens as you go down the group to the atomic radius?
The atomic radius gets larger. This is because extra electron shells are added as you go down the group
What happens to first ionisation energy as you go down group 2?
It decreases
Why does the first ionisation energy as you go down the group decrease?
Each element down group 2 has an extra electron shell compared to the one above
The extra shell means that outer electrons further away from the nucleus which greatly reduces the nuclear’s attraction
Making it easier to remove electrons
What happens to the positive charge of the nucleus as you go down group 2 metals and why doesn’t this matter?
It does increase as you down the group due to extra protons but this effect is overridden by the effect of the extra shells
What happens as you go down the group to the first ionisation energy?
The first ionisation energy decreases due to increasing atomic radius and shielding effect
What happens as you down the group 2 metals to the reactivity?
When group 2 elements lose electrons forming positive ions the easier it is to lose electrons the more reactive the element so reactivity increases down the group
What structure do group 2 metals tend to have?
Typical metallic structures with positive ions in a crystal structure surrounded by delocalised electrons from the outer electron shells
What happens as you go down group 2 that’s related to melting point?
The metal ions get bigger but the number of delocalised electrons stay the same and the charge on the ion also stays the same
The larger the ionic radius?
The further away delocalised electrons are from the positive nuclei and the less attraction they feel. So takes less energy to break the bonds meaning the melting point generally decrease as you down the group.
What’s the exception to this trend?
Blip at magnesium because crystal structure changes
What happens when group 2 elements are react with water?
They are oxidised from a state of 0 to +2 forming M2+ ions
M=>M2+ +2e-
Water is the oxidising agent
What happens to solubility down the group 2 elements?
Generally, the compounds of group 2 elements contain singly charged negative ions increase in solubility down the group whereas compounds contain doubly charged negative ions decrease down the group
Solubility of group 2 elements hydroxides?
Top element-magnesium- least soluble
Barium- most soluble
Group 2 metal solubility sulfate?
Magnesium is the most soluble
Barium is the least soluble
Details on the least soluble compounds of group 2 metals?
MgOH2 has very low solubility sparingly soluble
Most sulfates are soluble in water, barium sulfates is insoluble
How do you test for sulfate ions?
For acidified barium chloride is added to solution containing sulfate than a white precipitate of barium sulfate is formed.
You need to acidity solution with HCl to get rid of any lurking sulfites or carbonates which also produce a white precipitate
What are group 2 metals known as?
Alkaline earth metals
Many common compounds used to neutralise acids
What is calcium hydroxide used for?
Slake lime Ca(OH)2 is used in agriculture to neutralise acid soils
Magnesium hydroxide used for?
Used in some indigestion tablets as an antacid- substance which neutralises excess stomach acid
How do both of these work?
Ionic equation for neutralisation
H+ (aq)+ OH-(aq) => H2O (l)
What’s barium sulfate used for?
Barium meal
What are x-ray’s traditionally good for?
Finding broken bones but pass through soft tissue so soft tissue doesn’t show up like the digestive system don’t show up on conventional X- Ray pictures
How does barium sulfate work?
Opaque to X-Rays so doesn’t pass through it
Used in barium meals to help diagnose problems with oesophagus, stomach or intestines
Patient swallows barium meal which is a suspension of barium sulfate. Barium sulfate coats tissue making them show up on X-rays showing structure of the organs
What is magnesium used to do?
As part of the process of extracting titanium from its ore
What is the main titanium ore converted to?
Titanium IV oxide is first converted to titanium chloride by heating it with carbon in a stream of chlorine gas
Titanium chloride is then purified by fractional distillation before being reduced by magnesium in a furnace at almost 1000 oC
TiCl4(g)+2Mg(l)=> Ti(s)+2MgCl2(l)
Mg is the reducing agent
What does burning fossil fuels produce?
Sulfur dioxide which pollutes the atomsphere
What stops it polluting?
Acidic sulfur dioxide can be removed from four gases by reacting with an alkali (wet scrubbing)
Powdered calcium oxide and calcium carbonate can be used for this
Slurry is made from mixing calcium oxide or calcium carbonate with water. Sprayed onto four gases. Sulfur dioxide reacts with alkaline slurry and produces a waste product calcium sulfite
What are flue gases?
Gases emitted from industrial exhausts and chimneys
Reactions for flue gases?
Ca(s)+2H2O+SO2(g)-> CaSO3(s)+ 2H2O (l)
CaCO3(s)+2H2O(l)+SO2(g)=>CaSO3(s)+2H2O(l)+CO2(g)
Describe fluorine
F2 Pale yellow Gas 1s22s22p5 Most electronegative
Chlorine
Cl2 Green Gas 1s2 2s2 2p6 3s2 3p5 Second most electronegative
Bromine
Br2 Red-brown Liquid 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p5 Third most electronegative
Iodine
I2
Grey
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p5
Least electronegative
What happens to boiling points down the halogens?
Increases down the group
Due to increasing strength of van der Waals forces as the size and relative mass of the molecule increases.
How can electrons do group 2 elements have?
Two in their outer shell
S2
What happens to electronegativity through down group 7?
Electronegativity is the tendency of an atom to attract a bonding pair of electrons. The halogens are all highly electronegative elements. But larger atoms attract electrons less than smaller ones. This is because electrons are further away from the nucleus and are shielded by more electrons. It decreases
What happens when a halogen reacts?
They gain an electron.
Why do halogens get less reactive down the group?
The atoms become larger
The outer shell is further from the nucleus so electrons are less strongly attracted to it. So halogens become less oxidising down the group
Displacement of Iodine?
No reaction with F- Cl- Br-
Bromine displacement reaction
Br2 will displace I-
Br2(aq)+2I- =>2Br-(aq) +I2(aq)
Chlorine displacement reaction
Cl2 with displace Br- and I-
Cl2(aq)+2Br-(aq)=>2Cl-(aq)+Br2(aq)
Cl2(aq)+2I-(aq)=>2Cl-(aq)+I2(aq)
What can the relative oxidising strengths of halogens be seen in?
Their displacement reactions with halide
Basic rule for displacements
A halogen will displace a halide from solution if the halide is below it in the period table
How can these displacements reactions be used?
To help identify which halogen or halide is present in a solution
What happens when chloride water Cl2(aq) is added to potassium chloride solution KCl (aq) and what colour are they to begin with?
No reaction
Chloride water is colourless
Potassium chloride is colourless
What happens when Bromine water is added to potassium chloride?
No reaction
What colour is bromine water?
Orange
What happens when iodine solution is added to potassium chloride?
No reaction
Colour of iodine solution
Brown
What happens when potassium bromide solution is added to chlorine water?
Orange solution Br2 formed
Potassium bromide was colourless before
Bromine water and potassium bromide?
No reaction
Potassium bromide and iodine solution?
No reaction
Potassium iodide solution and chlorine water?
Brown solution formed
Potassium iodide solution add bromine water?
Brown solution formed
Potassium iodide solution and iodide solution?
No reaction
What is chlorine gas with cold, dilute, aqueous sodium hydroxide?
Sodium chlorate (I) solution
NaClO(aq)
Common household bleach (kills bacteria)
Ox. State of this?
2NaOH(aq)+Cl2=>
0
NaClO(aq)+NaCl(aq)
+1 -1 +H2O(l)
What’s disproportionation?
The element being oxidised and reduced
What is sodium chlorate (I) solution used for?
Bleach paper and textiles
Cleaning toilets
What happens when you mix chlorine with water?
Disproportionation
Cl2(g)+H20(l) 2H+(aq) 0
Cl- (aq) +ClO- (aq)
-1. +1
What happens in sunlight to chlorine?
Cl2(g)+H2O (l) 4H+(aq)+ 2Cl- (aq) +O2(g)
What does the fact chloride (I) ions kill bacteria mean?
Adding chlorine or a compound containing chlorate (I) ions to water can make it safe to drink or swim in
On the downside, chlorine is toxic
Why is drinking water treated in the UK?
To make it safe
Why is chlorine an important part of water treatment?
Kills disease- causing microorganisms
Some chlorine persists in the water and prevents reinfection further down the supply
Prevents the growth of algae eliminating bad tastes and smells and removes discolouration caused by organic compounds
What are some risks from using chlorine to treat water?
Chlorine gas is harmful if breathed in
Water change contains variety of organic compounds from the decomposition of plants. Chlorine reacts with compounds to form chlorinated hydrocarbons e.g. Chloromethane and many of these chlotinated hydrocarbons are carcinogenic
Why is chlorine harmful is breathed in?
it irritates the respiratory system. Liquid chlorine on skin or eyes causes severe chemical burns. Accidents involving chlorine can be serious and fatal.
Why is chlorine added when there’s a risk of it causing cancer?
The increased cancer is small compared to the risks from untreated water- a cholera epidemic could kill thousands of people
What do we have to do when making decisions whether to add chemicals to drinking water?
Weigh up risks and benefits
What do you need to reduce something?
The halide ions need to lose an electron from its outer shell. How easy this depends on the attraction between the nucleus and the outer electrons
The greater the reducing power?
The greater the reactivity and the faster reduction reactions will take place
Why is it as you go down the halogen group the attractions get weaker?
1) ions gets bigger so electrons are further away from the positive nucleus
2) extra inner electron shells so there’s greater shielding effect
The further down the group the halide ion is?
The easier it loses electrons and the greater its reducing power
Modern planes are made from?
Aluminium
What a good example of halogens doing some reducing?
The halogen/ halide displacement reactions
Reaction of NaF or NaCl with H2SO4 what happens words?
HF/ HCl(g) is formed. You’ll see misty fumes as gas comes into contact with moisture in air.
HF and HCl aren’t strong enough reducing agents to reduce sulfuric acid so reaction stops there. It’s not a redox reaction- oxidation states of halide and sulfur stay the same (-1 and +6)
NaF/ NaCl with H2SO4?
NaF(s)+H2SO4(aq)=> NaHSO4(s)+HF(g)
NaCl(s)+ H2SO4(aq)=> NaHSO4(s)+HCl(g)
Reaction of NaBr with H2SO4?
First reaction gives misty fumes of HBr (g)
HBr is stronger reducing agent than HCl and reacts with H2SO4 in a redox reaction
Reaction produces choking fumes of SO2 and orange fumes of Br2
Reaction of NaBr with H2SO4?
NaBr(s)+ H2SO4 (aq)=> NaHSO4(s) +HBr (g) 2HBr(aq)+H2SO4(aq)=> -1 +6 Br2(g)+SO2(g)+2H2O (l) 0. +4
Reaction of NaI with H2SO4?
Same initial reaction giving HI gas
HI then reduced to H2SO4
HI being very strong as far as reducing agents go keeps going and reduces SO2 to H2S
Solid iodine is also formed by this reaction
Chemical equations of NaI with H2SO4
NaI(s) +H2SO4(aq)=>NaHSO4(s)+HI(g) 2HI(g)+H2SO4(aq) => I2(s)+SO2(g) -1 +6 0 +4 +2H2O(l) 6HI(g)+SO2(g)=>H2S+3I2(s)+2H2O(l) -1 +4 -2 0
What is the test for halides?
Add dilute nitric acid to remove ions which might interfere with test. Then add few drops of silver nitrate solution (AgNO3(aq)) a precipitate is formed (of silver halide)
Ag+(aq) +X-(aq)=> AgX(s)
Precipitate fluoride test for halides?
No precipitate
Precipitate chloride test for halides?
White precipitate forms slowest
Precipitate bromide test for halides?
Cream precipitate middle speed
Precipitate iodide test for halides?
Yellow precipitate forms fastest
Then to be sure what can you do?
Test your result by adding ammonia solution. Each silver halide has a different solubility in ammonia
Chloride silver halide precipitate in ammonia?
White precipitate
Dissolved in dilute NH3(aq) most soluble
Bromide silver halide precipitate in ammonia?
Cream precipitate,
Dissolved in concentrated NH3(aq)
Middle solubility
Iodide silver halide precipitate in ammonia?
Yellow precipitate, insoluble in concentrated NH3(aq)
Least soluble
What do cations include?
Things like ions of group 2 metals and ammonium ions
How do identify group 2 ions?
Flame test
Compounds of some group 2 metals burn with characteristic colours.
How do you do the flame test?
Dip nichrome wire loop in concentrated HCl
Then dip wire loop into unknown compound
Hold the loop in clear blue part of Bunsen burner flame
Observe colour change
Colour change flame test
Ca2+ brick red
Sr2+ red
Ba2+ pale green
How can you test for ammonium gas? Way 1
It’s alkaline so you can use a damp piece of red litmus paper (litmus paper needs to be damp so ammonia gas can dissolve) if ammonia present the paper will turn blue
How do test for ammonium ions? Way 2
Add hydroxide ions to a solution containing ammonium ions they will react to produce ammonia gas and water:
NH4+ +OH- => NH3(g) + H2O(l)
Way to test for ammonia ions? 3
an use reaction to test whether a substance contains ammonium ions. Add some dilute sodium hydroxide solution to mystery substance in test tube and gently heat the mixture. If ammonia given off, ammonium ions must be present.
What can a anion include?
Halide ions, hydroxide ions, sulfate ions and carbonate ions
How do identify sulfate ions?
Add dilute HCl followed by barium chloride solution
Ba2+(aq)+SO4 2-(aq)=> BaSO4(s)
If white precipitate of barium sulfate firms it means the original compound contained a sulfate
Why is HCl added?
To get rid of any treated of carbonate ions before you do the test. (These would also produce a precipitate, so they’d confuse the results)
What can you use to test for OH- ions?
Make solutions alkaline so a solution containing OH- ions you can use a pH indicator to test it
1) dip piece of red litmus paper into solution
2) if hydroxide ions are present, the paper will turn blue
How do you test for halides?
With silver nitrate solution
For chloride, bromide and iodide ions you add dilute nitric acid followed by silver nitrate solution
Chloride gives you?
White precipitate of silver chloride
Bromide gives you?
Cream precipitate of silver bromide
Iodide gives you?
Yellow precipitate of silver iodide
How can you detect carbonates from hydrochloric acid? 1
When you add dilute HCl acid a solution containing carbonate ions will fizz because carbonate ions react with hydrogen ions in acid to give carbon dioxide
CO3 2-(s)+2H+ (aq)=> CO2(g)+H2O(l)
Name another way to detect carbonate?
Can test for carbon dioxide using limewater. Carbon dioxide turns limewater cloudy just bubble the gas through a test tube of limewater and watch what halogens. If limewater hoes cloudy, your solution contains carbonate ions
