4: Inorganic Chemistry and the Periodic Table Flashcards
What is the trend of reactivity in Group 2
Reactivity increases down Group 2 elements
Why does reactivity increase down Group 2
- First and second ionisation energies decrease down Group 2
- Therefore it is easier for the elements to lose their two valance electrons down the group
- This is due to the attraction of the nucleus and valance electrons decreasing down the group due to increasing atomic radii and the increasing shielding
How do Group 2 elements behave in redox reactions
- Each metal atom is oxidised, losing its two valance electrons, forming a +2 ion
- Another species gains these electrons and is reduced
- Therefore Group 2 elements are reducing agents
How can the reactivity of Group 2 elements be tested
- Reacting with dilute HCl: bubbles of hydrogen gas are given off much faster down the group (more vigorous)
- Reacting with oxygen: more reactive with oxygen down the group
What is the general equation for the reaction between Group 2 metals and oxygen
What is the general equation for the reaction between Group 2 metals and water
Why is magnesium oxide sometimes formed when magnesium reacts with water
- Magnesium reacts extremely slowly with cold water, and the solution formed is only slightly soluble
- When magnesium is heated in steam, it reacts vigorously to make magnesium oxide
What is the general equation for the reaction of Group 2 metals and chlorine gas
Are Group 2 oxides acidic or basic
- All are basic
- Apart from BeO which is amphoteric
Define amphoteric
A substance that can act as both an acid (proton donor) and a base (proton acceptor)
What happens when Group 2 oxides react with water
- They form alkaline solutions which become more alkaline down the group
Oxide + water ➡️ hydroxide
What is the general equation of the reaction between a Group 2 oxide and dilute hydrochloric/sulphuric acid
Metal oxide + dilute acid ➡️ metal salt (chloride/sulphate) + water
What happens when Group 2 metal hydroxides react with dilute acids
- Form colourless solutions of metal salts
- Except barium sulphate which is insoluble, making a white precipitate
Metal hydroxide + dilute hydrochloric/sulphuric acid ➡️ metal salt (chloride/sulphate) + water
What is the ionic reaction that takes place when Group 2 oxides react with water
What is the trend in alkalinity in Group 2 solutions
Increases down the group
Why does alkalinity of Group 2 hydroxides increase down the group
- Solubility of Group 2 hydroxides increases down the group,
- So the concentration of OH- ions in the solution increases, increasing the pH of the solution
- Making it more alkaline
What is the general equation for Group 2 hydroxides dissolving in water
What is the trend of solubility in Group 2 sulphates
Solubility decreases down the group
What is the trend of solubility of Group 1 hydroxides and sulphates
They are all soluble in water
Are Group 1 or 2 hydroxides more soluble
Group 1 hydroxides are more soluble
What is thermal decomposition
The breakdown of a compound into two or more different substances using heat
What is the only Group 1 carbonate that decomposes
- Only lithium carbonate can be thermally decomposed at Bunsen temperatures
What is the general equation for the thermal decomposition of Group 2 carbonates
What is the only Group 1 nitrate that thermally decomposes
- Lithium nitrate
What is the general equation for the incomplete decomposition of Group 1 nitrates (not lithium)
What is the general equation for the thermal decomposition of Group 2 nitrates
What is the trend in thermal stability in Group 1 and 2 carbonates and nitrates
Thermal stability increases down both groups
Why does thermal stability increase down Group 1 and 2 carbonates and nitrates
- Ionic radius of the cations increases down the groups
- Positive ions with larger ionic radii have lower polarising power and distort the electron clouds of the anions less
- Positive ions with smaller ionic radii have higher polarising power and distort the electron clouds one the anions more
- The more polarised the anion is, the more likely it is to be thermally decomposed as the bonds in the carbonate and nitrate ions become weaker and less heat is needed to free CO2 and NO2
Describe the flame test process
- Dip an unreactive metal wire (in chrome/platinum) in concentrated HCl, then hold it in the blue flame of the Bunsen burner until there is no colour change (cleans to avoid contamination)
- Dip the wire in the solid metal sample and place it on the edge of the blue Bunsen flame
- Observe the colour
Why are are colours produced in flame tests
- Heat causes electrons in the sample to jump to a higher energy level
- The electron is unstable at this energy level, so falls back down
- As it falls energy is emitted in the form of visible light
Mg2+ flame test
Bright white flame
Ba2+ flame test
Apple green
Ca2+ flame test
Brick red
Sr2+ flame test
Strong red
Cu2+ flame test
Blue-green
K+ flame test
Lilac
Na+ flame test
Yellow
Li+ flame test
Scarlett red
Rb+ flame test
Red
Cs+ flame test
Blue
What is the name of Group 7 elements
Halogens
What is the trend in colour of Group 7 elements
Colour gets darker down the group
What is the colour and standard state of fluorine
Pale yellow gas
What is the colour and standard state of chlorine
Green/yellow gas
What is the colour and standard state of bromine
Orange/brown liquid
What is the colour and standard state of iodine
Black solid (purple vapour)
Define volatility
How easily a substance can evaporate
What is the trend in volatility in Group 7
Volatility of the halogens decreases down the group
What is the trend in melting/boiling points in Group 7 elements
Melting/boiling point of the elements increases down the group
Why does the boiling point of halogens increase down the group
- Halogens are diatomic molecules with simple molecular structures, with instantaneous dipoles caused by uneven spread of electrons within the molecule
- There are weak London forces between the diatomic molecules caused by instantaneous dipole induced dipole forces
- The more electrons in a molecule, the greater the instantaneous dipole induced dipole forces, and the stronger the London forces between molecules
- This causes more energy needed to separate the molecules, causing the melting/boiling points to increase down the group
What is the trend in electronegativity in Group 7 elements
Electronegativity decreases down the group
Define electronegativity
The electronegativity of an atom refers to how strongly it attracts electrons towards itself in a covalent bond
Why does electronegativity decrease down Group 7
- Going down the group, atomic radii of the elements increases, so valance electrons get further from the nucleus as there are more shells in between it
- Incoming electrons experience more shielding from the attraction of the positive nuclear charge
- Making it harder for the elements to accept an electron (oxidising power) down the group
What is the trend in reactivity in Group 7 elements
Reactivity decreases down the group
Why does reactivity decrease down Group 7
- When halogens react they gain 1 electron, and are reduced as they act as oxidising agents
- As atomic radii increases down the group, valance electrons are further away from the nucleus, and are shielded from the positive nucleus
- This makes it harder for the elements to attract an electron down the group
Describe the reaction of fluorine and hydrogen
Reacts explosively even in cool, dark conditions
Describe the reaction of chlorine and hydrogen
Reacts explosively in sunlight
Describe the reaction of bromine and hydrogen
Reacts slowly on heating
Describe the reaction of iodine and hydrogen
Forms an equilibrium mixture on heating
What is shown by halogen displacement reactions
- The reactivity of the halogens
- The more reactive halogen can displace a less reactive halogen from a halide solution of the less reactive halogen
What is the overall equation and ionic equation of chlorine water being added to a solution of bromine water
Write the overall equation and ionic equation of chlorine water being added to a solution of iodine water
What happens when chlorine is added to bromine solution
- Chorine is more reactive, so displaces the bromine ions in the solution
- Therefore the solution turns yellow-orange as Br2 is formed
What happens when chlorine and cyclohexane are added to bromine solution
- Chlorine is more reactive so it displaces bromine in the solution
- Cyclohexane will form an organic layer on top of the solution, and it will be yellow-orange as Br2 is formed
Why is cyclohexane used in halogen displacement reactions
Halogens are more soluble in the organic layer created by the cyclohexane, so the colour changes can be observed more easily
What happens when chlorine and cyclohexane are added to iodine solution
- Chlorine is more reactive so it displaces iodine in the solution
- The cyclohexane forms an organic layer on top of the solution, and it turns purple as I2 is formed
What happens when chlorine is added to iodine solution
- Chlorine is more reactive so it replaces iodine in the solution
- Therefore the solution turns brown as I2 is formed
Write the full equation and the ionic equation of bromine water and iodine water
What is the general formula for halogens reacting with metals
Halogen + metal ➡️ metal halide salt
- Where the metal is oxidised
- The halogens act as oxidising agents
What are the halogens reactions with iron (II)
- Chlorine and bromine can oxidise iron(II) to iron(III)
- Iodine isn’t a strong enough oxidising agent, and is instead oxidised itself from iodide ions to iodine by iron(III)
What is the reaction, ionic equation, and half equations of chlorine in dilute hot alkali (70 degrees C)
- Disproportion reaction, as chlorine is simultaneously reduced and oxidised
What is the reaction, ionic equation, and half equations of chlorine in dilute cold alkali (15 degrees C)
Why is chlorine added to drinking water, and what is the reaction
- Chlorine used to clean water and make it drinkable
- Disproportionation reaction
- Chloric(I) acid (HClO) sterilises water by killing bacteria
- HClO can further dissociate in water to form ClO- which also acts as a sterilising agent
What generally happens in the reaction between halide ions and concentrated sulphuric acid
- React to produce toxic gases, so should happen in a fume cupboard
What happens when chloride ions react with concentrated sulphuric acid
- Conc. H2SO4 is added dropwise to sodium chloride crystals
- Producing hydrogen chloride gas
- The HCl gas produces steamy white fumes
What happens when bromide ions react with concentrated sulphuric acid
- After the reaction has occurred and HBr has been formed, the conc. sulphuric acid oxidises HBr
- The HBr decomposes into bromine and hydrogen gas, and the sulphuric acid is reduced to sulphur dioxide gas
- Bromine makes a reddish-brown gas
What happens when iodide ions react with concentrated sulphuric acid
- The reaction occurs, and the HI produced is oxidised by the sulphuric acid
- The HI can be oxidised by sulphuric acid into iodine, and itself is reduced to sulphur
- Iodine has a purple vapour, and sulphur is a yellow solid
- The sulphuric acid can also oxidise HI to iodine, and itself is reduced to hydrogen sulphide
- Hydrogen sulphide smells of rotten eggs
Describe the test for halide ions
- Unknown halide solution is dissolved in nitric acid
- Silver nitrate solution is added
- A precipitate of silver halide is formed
- Dilute ammonia is added to the solution
- Concentrated ammonia is added to the solution
Silver ion test for chloride results
- If chloride is present, ions form a white precipitate
- When dilute ammonia is added, precipitate dissolves
- When concentrated ammonia is added, precipitate dissolves
Silver ions test for bromide results
- If bromide is present, precipitate turns cream
- When dilute ammonia is added, precipitate remains insoluble
- When concentrated ammonia is added, precipitate dissolves
Silver ions test for iodide results
- If iodide is present, precipitate turns pale yellow
- When dilute ammonia is added, solution remains insoluble
- When concentrated ammonia is added, solution remains insoluble
What is the equation for the reaction between halogens and hydrogen
- Reaction produces a hydrogen halide
What is the equation for the reaction between hydrogen halides and ammonia gas
- Produces ammonium halides
What is the equation for hydrogen halides reacting with water
- Dissolve in water to form acids
