Chapter 4 - Inorganic chemistry and the Periodic table (L) Flashcards
What is the definition of first ionisation energy?
The energy required to remove an electron from each atom in one mole of atoms in gaseous state
What is the definition of second ionisation energy?
The energy required to remove an electron from each 1+ ion in one mole of 1+ ions in gaseous state
What is the base cause of a high or low ionisation energy?
A high or low electrostatic attraction between the nucleus and outermost electron
What is electron shielding, and what is its effect on ionisation energy?
The idea that inner electrons shield the outer electrons from the electromagnetic pull of nucleus, weakening their attraction.
This hence decreases ionisation energy, as it is not as difficult to remove the outer electron
What are the 3 main factors to consider when explaining trends in ionisation energy?
- Nuclear charge
- Number of shells
- Electron shielding
What is the trend in reactivity down group 2?
Reactivity increases down the group, as less energy is required to remove the 2 outer electrons as you go down the group (first and second ionisation energy)
What is the trend in the vigorousness of reactions down group 2?
As you go down group 2, the reactions become more vigorous
What happens between group 2 elements and oxygen even without heating?
A slow reaction occurs, in which a surface coating of oxygen forms around the element, helping prevent further reaction
How is barium often stored and why?
Because it is the most reactive, it is often stored under oil to keep it reacting with oxygen and water vapour in the air
What is the general formula for group 2 reactions with oxygen? (M = group 2 element)
2M(s) + O2(g) -> 2MO(s)
What is the general formula for group 2 reactions with chlorine? (M = group 2 element)
M(s) + Cl2(g) -> MCl2
What is effervescence?
Bubbles in a liquid (fizz)
What is seen in the reactions with group 2 elements with water as you go down the group?
Increasing effervescence
What is the general formula for group 2 reactions with water? (M = group 2 element)?
M(s) + 2H2O(l) -> M(OH)2(aq) + H2(g)
What is the exception to the general formula for group 2 reactions with water?
Calcium, which forms a solid rather than aqueous hydroxide- Ca(OH)2 (s)
What is the formula for when Mg is heated in steam?
Mg(s) + H2O(g) -> MgO(s) + H2(g)
Why is hydrogen burned as it leaves the tube?
So it forms H2O, so there is not a highly flammable gas floating around in the lab
Why is it not a good idea to use water to put out a magnesium fire?
Because the magnesium will react with the water, feeding the fire more oxygen and releasing flammable hydrogen gas, which will further feed the fire
What type of oxides are group 2 oxides?
Basic oxides
What are basic oxides?
Oxides that can react with water to form alkalis
What is the general formula for group 2 oxides reacting with water?
MO(s) + H2O(l) -> M(OH)2 (aq)
What is the trend in solubility down group 2?
As you go down the group, solubility increases
What is the trend in the alkalinity of solution produced down group 2?
As you go down the group the pH (alkalinity) increases
What can be used to test for carbon dioxide?
Calcium hydroxide (limewater)- goes milky as a white precipitate forms. Calcium reacts with CO2 to form calcium carbonate (white precipitate)
What is milk of magnesia and what does it do?
Magnesium hydroxide- it reacts with HCl in the stomach, neutralising it
What do all group two oxides and hydroxides react with acids to form?
Salts and water (neutralisation reactions)
Example of how group 2 hydroxides are used in agriculture
Calcium hydroxide is used to neutralise excess acidity in soil
What is the solubility of group 2 nitrates and chlorides?
All group 2 nitrates and chlorides are soluble
What is the trend in the solubility of group 2 sulfates?
The solubility of group 2 sulfates decreases down the group
What solubility is magnesium sulfate classed as?
Magnesium sulfate is soluble
What solubility is calcium sulfate classed as?
Calcium sulfate is slightly soluble
What solubility is strontium and barium sulfate classed as?
Insoluble
How can you use barium ions to test for sulfate ions?
A solution containing barium ions can be added, and any sulfate ions will react with the barium ions to form a white precipitate of barium sulfate
Why is an acid also added alongside the barium ions to test for sulfate ions?
To prevent barium ions reacting with carbonate ions, which would also form a white precipitate
How and why are barium meals used?
Solutions containing barium ions are poisonous to humans, however barium sulfate is insoluble so not poisonous (as the ions cannot move).
Barium meals are used to make soft tissues show up more clearly in x-rays
What is thermal stability?
The measure of the extent to which a compound decomposes when heated
What is the difference in thermal stability between group 1 and 2?
Group 1 compounds are more thermally stable than group 2 compounds
What are 2 reasons why group 1 compounds are more thermally stable than group 2 compounds?
- Group 2 cations have double the charge
- The ionic radius of group 2 cations is smaller (in the same period)
What is the trend in ionic radius of group 2 cations?
As you go down the group, ionic radius increases
What do all group 1 and 2 nitrates decompose to when heated?
Nitrites (lesser decomposition) or oxides (greater decomposition)
What are the brown fumes that are given off during the decomposition of nitrates?
Nitrogen dioxide
What does brown fumes not being given off indicate?
Lesser decomposition
What does brown fumes being given off indicate?
Greater decomposition
What is the word equation for lesser decomposition of nitrates?
Metal nitrate -> metal nitrite + oxygen
What is the word equation for greater decomposition of nitrates?
Metal nitrate -> metal oxide + nitrogen dioxide + oxygen
What type of decomposition occurs in group 2 nitrates, and what does this mean brown fumes wise?
All group 2 nitrates have greater decomposition, which means they will give off brown fumes
What type of decomposition occurs in group 1 nitrates, and what does this mean brown fumes wise?
Group 1 nitrates have lesser decomposition, which means they will not give off brown fumes.
EXCEPT FOR ONE EXCEPTION- LITHIUM NITRATE
What is the one exception to group 1 nitrates decomposition and why?
Lithium nitrate- this is because it is the smallest group 1 cation
What are the two possibilities of decomposition of group 1 and 2 carbonates?
They either don’t decompose, or decompose to oxides and give off carbon dioxide
What is the word equation for the decomposition of carbonates?
Metal carbonate -> metal oxide + carbon dioxide
Do group 2 carbonates decompose?
Yes. All group 2 carbonates decompose to a metal oxide, giving off carbon dioxide
Do group 1 carbonates decompose?
No. Group 1 carbonates do not decompose.
EXCEPT FOR ONE EXCEPTION- LITHIUM CARBONATE
What is the one exception to the decomposition of group 1 carbonates and why?
Lithium carbonate- this is because it is the smallest group 1 cation
What observations can be made for the decomposition of carbonates and why?
No observations can be made.
Both carbonate and oxides are white solids, and carbon dioxide is given off, which is colourless
Why does a greater charge on the cations lead to a lower thermal stability?
Because a greater charge will result in a higher level of electron distortion, making it more unstable
Why does a smaller size result in a higher level of distortion?
It means the cation will have a higher charge density, which will result in a higher level of electron distortion, making it more unstable
What do flame tests identify?
The presence of a cation in a compound
What equipment must you use for flame tests?
- Safety glasses
- Lab coat
- Fume cupboard
- Bunsen burner
In flame tests, what should you add to the metal compound and why?
Concentrated hydrochloric acid, so the metal compound begins to dissolve
What type of metal should the metal wire be in flame tests?
Platinum or nichrome wires
What do you use the metal wire for in flame tests?
Dip it into the mixture to obtain a sample of the compound, then hold the end of the wire in the flame and observe the colour
What can you use instead of platinum or nichrome wires
Silica rods
What are the 2 main problems with flame tests?
- Compounds may contain sodium impurities, and the intense colour of sodium may mask other colours
- Describing colours is subjective, meaning word descriptions of the flame may mean different colours to different people
What flame colour is lithium?
Red
What flame colour is sodium?
Yellow/orange
What flame colour is potassium?
Lilac
What flame colour is rubidium?
Red/purple
What flame colour is caesium?
Blue/violet
What flame colour is beryllium?
No colour
What flame colour is magnesium?
No colour
What flame colour is calcium?
Brick red
What flame colour is strontium?
Crimson red
What flame colour is barium?
Apple green
Why is concentrated hydrochloric acid used in flame tests?
Conc. HCl converts the compounds into their metallic chlorides, which is important because, the metallic chlorides are very much volatile, so are more likely to give stronger results
What causes the colours in a flame test to appear?
When electrons absorb energy, they move to higher energy levels, and then back down again. This releases energy- if this energy corresponds to radiation in the visible light spectrum, then a flame test colour appears.
What is the ground state of an atom?
When an atom has all its electrons in their lowest possible energy levels
What is the excited state of an atom?
When an atom gains energy and moves to a higher energy level
What is the test for ammonium ions?
Warm with sodium hydroxide- releases ammonia gas
How can you test for the presence of ammonia gas?
- Damp red litmus paper turns blue
- Reacts with hydrogen chloride gas to form white fumes (ammonia chloride)
What are the group 7 elements known as?
Halogens
What is the general trend in melting point down group 7?
As you go down group 7, the melting point increases
What elements are gas at room temperature in group 7?
Fluorine and chlorine
What elements are liquid at room temperature in group 7?
Bromine
What elements are solid at room temperature in group 7?
Iodine and astatine
What determines the melting temperature of group 7 elements?
The strength of the London forces between molecules
Why does the strength of the London forces increase down group 7?
As you go down group 7, the number of electrons increases. More electrons = bigger/more polar instantaneous dipoles = bigger/more polar induced dipoles = greater strength of electromagnetic attraction between the dipoles
What is sublimation, and what group 7 element does it happen to?
Sublimation is where a solid turns directly into a gas. This happens to iodine
What is the trend in electronegativity in group 7?
As you go down the group, electronegativity decreases
Why does electronegativity decrease down group 7?
As you go down the group, both the atomic radius and amount of electron shielding increase, meaning there is a greater distance between the nucleus and bonding pair electrons and a weaker electrostatic attraction.
What is electron shielding?
The idea that electrons in inner shells shield the outer shell from the pull of the nucleus, causing the outer electrons to feel a weaker, shielded nuclear attraction
What is the trend in reactivity down group 7?
As you go down the group, reactivity decreases
Why does reactivity decrease down group 7?
Because atomic radii increases. Greater distance from positive nuclei = less positive attraction = harder to attract and gain an electron
What is the trend in the oxidising power of halogen molecules down group 7?
As you go down the group, oxidising power decreases
What is the trend in the reducing power of halide ions down group 7?
As you go down the group, reducing power increases
What does bromine displace?
Iodine but not chlorine
What does chlorine displace?
Iodine and bromine
What does iodine displace?
Neither chlorine nor bromine
What does it mean to have a strong oxidisation power?
It can easily oxidise the other thing (a good oxidising agent) i.e. is good at gaining electrons
What is disproportionation?
Where a substance is both oxidised and reduced in the same reaction
Why are iodide ions better reducing agents than chloride ions?
There is a weaker attraction in iodide ions between the outer electrons and the nucleus (due to the larger size), so iodide ions can more easily lose an electron, making it a better reducing agent
What does it mean to have a strong reducing power?
It can easily lose electrons, and hence reduce the other thing (a good reducing agent)
What observation will you see when you add (sodium) chloride to sulfuric acid?
Misty fumes
What products are formed when you react (sodium) chloride with sulfuric acid?
Hydrogen chloride (HCl)
What happens when you react (sodium) bromide with sulfuric acid?
Initially, hydrogen bromide is produced.
However the HBr produced then reacts with the sulfuric acid again, producing Br2 and sulfur dioxide
Why is only hydrogen chloride produced when you add (sodium) chloride to sulfuric acid?
Because it’s not a strong enough reducing agent to reduce the sulfuric acid
Is reacting (sodium) bromide with sulfuric acid a redox reaction?
Initially no.
However, as the HBr goes on to react with the sulfuric acid, that is a redox reaction, as the sulfuric acid is reduced and the Br oxidised
What observation will you see when you add (sodium) bromide to sulfuric acid?
Hydrogen bromide = misty fumes
Bromine = brown fumes
Sulfur dioxide = choking smell
What happens when you react (sodium) iodide with sulfuric acid?
Everything that happened in the bromide + sulfuric acid reaction, but then one step further.
The HI will then react with the sulfur dioxide produced, forming hydrogen sulfide.
Sulfur is also produced.
What is produced when you react (sodium) iodide with sulfuric acid?
Hydrogen iodide = misty fumes Iodine = purple fumes Sulfur dioxide = choking smell Sulfur = yellow solid Hydrogen sulfide = rotton egg smell
What is produced when you react hydrogen bromide/iodide with sulfuric acid?
Hydrogen bromide/iodide + sulfuric acid -> sulfur dioxide + water + bromine/iodine
Overall, what happens in the reaction between bromide and sulfuric acid?
Bromide ions reduce the sulphuric acid to sulphur dioxide. In the process, the bromide ions are oxidised to bromine
Overall, what happens in the reaction between iodide and sulfuric acid?
Iodide reduces the sulfuric acid: first to sulphur dioxide then to sulphur itself and all the way to hydrogen sulphide. The iodide ions are oxidised to iodine
What is are some problems in interpreting colour changes in group 7 displacement reactions?
The similarity of colours between group 7 elements
Colour variation dependent on concentration
Why is it a good idea to add an organic solvent like cyclohexane after group 7 displacement reactions?
Halogens are more soluble in cyclohexane than water, so the halogen dissolves in the organic layer, where its colour can be more easily seen
What is the reaction between chlorine and water an example of?
Disproportionation, as the chlorine is both oxidised and reduced
What are the two products from the reaction between chlorine and water?
HCl + HClO
What is the difference when chlorine is reacted with hot compared to cold alkali?
When chlorine is reacted with cold alkali, it forms sodium chlorate (I), whereas when chlorine is reacted with hot alkali, it forms sodium chlorate (V)
What is the purpose of adding chlorine to water?
Disinfects water by killing pathogens
What is sodium chlorate (I) used as?
It is the active ingredient in household bleach
What is sodium chlorate (V) used as?
It is also used in bleaching, and as a weed killer
In testing for halides in solution, why is nitric acid used beforehand?
To make sure any other anions (in particular carbonate ion) are removed, as they would otherwise also form precipitates
Why do we need to test for halides in solution?
They are colourless so indistinguishable
What can you observe when you add silver nitrate to a fluoride solution?
There is no visible change- this is because silver fluoride is soluble
What can you observe when you add silver nitrate to a chloride solution?
A white precipitate will be formed
What can you observe when you add silver nitrate to a bromide solution?
A cream precipitate will be formed
What can you observe when you add silver nitrate to an iodide solution?
A yellow precipitate will be formed
Why do we after adding silver nitrate, add dilute aqueous ammonia and concentrated aqueous ammonia?
As after just adding the silver nitrate, it might be difficult to clearly distinguish which colour the precipitate is i.e what halide is present. So further tests are done to fully prove which halide is present
Which halide precipitate disappears after the addition of dilute aqueous ammonia?
(Silver) chloride
Which halide precipitates do not disappear after the addition of dilute aqueous ammonia?
(Silver) bromide and iodide
Which halide precipitate disappears after the addition of concentrated aqueous ammonia?
(Silver) bromide. (Silver chloride would also disappear however it should already be gone from the addition of dilute aqueous ammonia)
Which halide precipitate should remain present throughout the addition of both dilute and concentrated aqueous ammonia?
(Silver) iodide
What is the general ionic equation for the formation of the precipitates?
Ag+(aq) + X-(aq) –> AgX(s)
What is the difference between hydrogen chloride and hydrochloric acid?
Hydrogen chloride is a gas.
Hydrochloric acid is aqueous
What acid is formed when hydrogen fluoride is added to water?
Hydrofluoric acid
What acid is formed when hydrogen chloride is added to water?
Hydrochloric acid
What acid is formed when hydrogen bromide is added to water?
Hydrobromic acid
What acid is formed when hydrogen iodide is added to water?
Hydriodic acid
What is the general equation for the reaction of hydrogen halide + water?
HX + H2O –> X- + H3O+
How is hydrofluoric acid different to the other halide acids?
It is a weak acid. In the reaction between HF + H2O is reversible
What happens when hydrogen halides react with ammonia gas?
A white ionic salt is formed
What is the general equation for the reaction between ammonia gas and hydrogen halides?
NH3(g) + HX(g) –> NH4X(s)
How do you react ammonia gas and hydrogen halides (e.g. chloride)?
You soak cotton wool pieces in concentrated aqueous ammonia and concentrated hydrochloric acid respectively, and put them in a tube.
The cotton wool pieces will give off ammonia and hydrogen chloride gas, which will move through the tube to meet and form the white salt ammonium chloride.
