Topic 4 (Group 1 and 2) - Inorganic Chemistry and the Periodic Table Flashcards
What are the group 2 elements also known as?
The Alkali Earth Metals
What charge of ions do metals in group 2 form?
2+
Describe an explain the first and second ionisation energies down the group 2 elements
- The first and second ionisation energies decrease
- Increase in distance between nucleus and valence electrons
- Shielding increases as the number of filled shells increases, therefore the effective nuclear charge decreases
- The effect of the increased shielding outweighs the increase in nuclear charge of the element
Describe an explain the trend in ionic radii down the group 2 elements
- Ionic radius increases
- The number of filled inner shells increases
Describe an explain the trend in reactivity down the group 2 elements
- Reactivity increases
- Due to it becoming easier for the valence electrons to be lost as the EFA’s between these electrons and the nucleus decreases
What oxidation states do metals in group 2 form? Why?
+2, as 2 electrons are lost from the outer s orbital
Compare the size of the group 2 ions to their atoms
- Group 2 ions are smaller than their atoms
- No. of electrons has decreased but the nuclear charge is still the same for each ion
- The valence electrons are closer to the nucleus
- Less shielding from filled inner shells
- Therefore, EFA’s between the nucleus and valence electrons has increased
Compare the ionic radii of the group 1 metals versus the group 2 metals?
As you go down the group the radii of the groups 1 ions will increase more than the radii of the group 2 metals. This is because group 2 ions have a greater nuclear charge so there are stronger EFA’s between the outer electrons and the nucleus.
Do the group 2 metals react with water/steam?
yes
Are the reactions of group 2 metals with water/steam more or less vigorous than with group 1 metals?
less vigorous
Which group 2 elements react with water/steam?
Mg -> Ba
Does Be react with water/steam?
no - it requires temperatures of 750 degrees C to react as the sum of the 1st and 2nd ionisation energies is much larger comparative to the other group 2 elements
What do group 2 metals act as in reactions?
reducing agents (they are oxidised)
What are the observations of the group 2 elements Be -> Ba when reacted with cold water
Be - unreactive
Mg - almost unreactive (some bubbles of hydrogen form on the surface, sight dip in water level)
Ca - hydrogen bubbles (effervescence) produced, white ppt. of Ca(OH)2 formed
St - many hydrogen bubbles ( vigorous effervescence) produced, white ppt. of St(OH)2 formed
Ba - most hydrogen bubbles (most vigorous effervescence) produced, white ppt. of Ba(OH)2 formed
How much white solid do you observe from the reaction of group 2 metals with cold water as you go down the group?
Less as you go down the group - the white solid becomes more soluble in the alkali solution
Write the equation for the reaction of Magnesium with cold water?
Mg(s) + 2H2O (l) -> Mg(OH)2 (s) + H2 (g)
What type of solution is formed form the reaction of group 2 elements with cold water?
Alkaline solutions
Write the general equation for the reaction of Ca, St and Ba with cold water?
M (s) + 2H2O (l) -> M(OH)2 (aq or s) + H2 (g)
What is the main difference between the reactions of group 2 metals with cold water versus with steam? Why?
The reactions are a lot more vigorous with steam as a greater proportion of particles have the required Ea to react
What are the observations of the group 2 elements Be -> Ba when reacted with steam?
Be - unreactive
Mg - bright white flame, white powder of MgO, hydrogen gas produced
Ca - white powder of CaO, hydrogen gas produced
St - white powder of StO, hydrogen gas produced
Ba - white powder of BaO, hydrogen gas produced
NB: Reactivity still increases down the group
Describe the set up for the reaction of Group 2 metals with steam
- Horizontal test tube with wool soaked in water at the curved end of it
- The test tube is fitted with a bung with tubing connected to a downturned test tube in water
- The group 2 metal is placed in the centre of the horizontal test tube
- The water soaked wool is then heated using a bunsen burner
- Effervescence should be produced in the downturned test tube
Write the general equation for the reaction of Ca, St and Ba with steam
M (s) + H2O (g) -> MO (s) + H2 (g)
Which group 2 metals burn in oxygen?
Mg -> Ba
Write the general equation for the reaction of group 2 metals with oxygen
2M (s)+ O2 (g) -> 2MO (s)
What are the observations for each of the reactions of group 2 metals with oxygen?
Mg - Bright white flame, white solid produced
Ca - Bright red flame, white solid produced
St - Bright white flame (red tinges around the edges), white solid produced
Ba - Bright green flame
Which group 2 metals from a different compound when burnt in an excess of oxygen?
St and Ba
Write a general equation for the reaction of group 2 metals with excess oxygen
M (s) + O2 (g) -> MO2 (s)
What is the peroxide ion?
O2 (2-)
What is the definition of a basic oxide?
A metal oxide that reacts with acids to form salts and water.
What is the definition of an alkali?
A soluble base
What is the definition of a base?
A proton accepter
Which group 2 metals react with Cl2?
All of them
Write a general equation for the reaction of the group 2 elements with chlorine
M (s) + Cl2(g) -> MCl2 (s)
What conditions do you need to provide in order for the group 2 elements to react with chlorine?
Heat
What is the observation when group 2 elements reaction with chlorine upon heating?
A white solid forms
Which metal oxides in group 2 act as basic oxides?
Mg -> Ba
What group 2 compounds act as bases in neutralisation reactions with dilute acids?
oxides and hydroxides
Write the general reaction of group 2 oxides with water
MO (s) + H2O (l) -> M(OH)2 (aq)
Write the equation for the reaction Barium Hydroxide with Hydrochloric Acid
Ba(OH)2 (s) + 2HCl (aq) -> BaCl2 (aq) + 2H2O (l)
Write the equation for the reaction of Magnesium Oxide with Hydrochloric Acid
MgO (s) + 2HCl (aq) -> MgCl2 (aq) + H2O (l)
What is the general equation for a neutralisation reaction?
acid + base -> salt + water
What is the general equation for a metal + acid reaction?
metal + acid -> salt + hydrogen
What is the trend in solubility of group 2 hydroxides down the group?
solubility increases
What is the trend in solubility of group 2 sulfates down the group?
solubility decreases
What is the way to remember the solubility rules?
HAM SALAD
hydroxides are more, sulphates are less, as descended
What is the use of the insoluble compound barium sulphate?
As a medical tracer for x-ray imaging as it cant be absorbed into the blood
What is the test for sulphate ions?
- Add a few drops of HCl to your solution containing sulphate ions
- Add a soluble barium salt e.g barium chloride or barium nitrate
- A white ppt. of barium sulphate forms if sulphate ions are present
Why do you need to add a few drops of HCl to your solution containing sulphate ions before adding your soluble barium salt?
To remove any carbonate impurities as these would produce a false positive (a white ppt.) when the barium compound was added
What is the general equation for an acid + carbonate reaction?
acid + carbonate -> salt + carbon dioxide + water
What is the ionic equation for barium and sulphate ions in the test for sulphate ions?
Ba(2+) (aq) + SO4(2-) (aq) -> BaSO4 (s)
How do you test for the trends in solubility of the group 2 hydroxides and sulphates?
- Add solutions of your group 2 metal chlorides to test tubes
- Add drops of hydroxide and sulphate solutions to each of them individually and record how many drops it takes for a ppt. to appear
Describe how to conduct a flame test
- Take a nichrome (or platinum) wire and dip it in conc. HCl. Hold the wire above the cone of the roaring bunsen burner. Repeat until the wire is clean/ no colour is observed when doing this.
- Dip the wire into the conc. HCl and then into a small amount of the compound that you are analysing. Hold the sample in the flame and note the colour that the flame turns
- Clean the wire thoroughly so that no traces of that compound remain (step 1)
- repeat the experiment with other compounds
What are the colours produced in the flame test for:
sodium
lithium
potassium
magnesium
calcium
strontium
barium
copper
sodium - strong persistent yellow
lithium - scarlet red
potassium - lilac
magnesium - no colour
calcium - brick red
strontium - red
barium - green
copper - blue/green
Why, when conducting a flame test, do you have to dip the nichrome wire in conc. HCl twice?
1 - To remove impurities from other compounds
2 - to form a volatile chloride with the compound you are testing -> this gives a clearer colour
Why do we observe different colours for different compounds during a flame test?
- When the electrons are heated they get excited and absorb energy. This causes them to go form a ground state to a higher energy orbital.
- When the electrons de-excite they release this energy
- The energy released corresponds to a specific wavelength of light from the visible light spectrum -> hence we observe that colour
Why does magnesium not produce a colour in the flame test?
As the wavelength emitted when the electron de-excites is outside of the visible spectrum
What is the definition of thermal stability?
An indication of the ease by which compounds decompose upon heating
Which compounds of group 1 and 2 metals undergo thermal decomposition?
Nitrates and Carbonates
What is the definition of thermal decomposition?
The breaking down of 1 compound into 2 or more products by heat
What is the general equation for the thermal decomposition of group 2 carbonates?
MCO3 -> MO + CO2
metal carbonate -> metal oxide + carbon dioxide
What is the general equation for the thermal decomposition of group 2 nitrates?
2M(NO3)2 -> 2MO + 4NO2 + O2
metal nitrate -> metal oxide + nitrogen dioxide + oxygen
What is the general equation for the thermal decomposition of group 1 nitrates?
2MNO3 -> 2MNO2 + O2
metal nitrate -> metl nitrite + oxygen
Why wont group 1 carbonates undergo thermal decomposition upon heating in a lab?
They require extremely high temperatures to do so
Which element in group 1 follows the same decomposition reactions as group 2?
lithium
Write the equation for the thermal decomposition of lithium nitrate
4LiNO3 -> 2Li2O + 4NO2 + O2
What is the trend in thermal stability as you go down groups 1 and 2?
The compounds become more thermally stable - require more heat energy to undergo thermal decomposition
What two factors affect thermal stability of compounds?
The:
- Charge of the cation
- Ionic radius of the cation
What is the term used to describe how easily a cation can distort an anion?
polarising power
What is the definition of polarising power?
The indication of the extent to which cations are able to distort the negative electron cloud around a neighbouring anion
Explain why thermal stability decreases as you ascend groups 1 and 2
- As you ascend the group the ionic radius increases
- The ions are more charge dense, therefore, their polarising power increases and the anion is distorted more
- The X - O bonds in the anion are weakened more, meaning that less heat energy is required to break down the compound
Why are group 1 nitrates more thermally stable than group 2 nitrates?
As there ions only have a 1+ charge, therefore the NO3(-) ions are less polarised so the N - O bonds are weakened less
Which group of nitrates/carbonates will, in general, require more heat energy to undergo thermal decomposition?
Group 1
What is an ionic equation?
An equation that describes a full chemical equation by only showing the reacting ions in solution. These equations should be balanced for both reacting moles and charges.
What is the definition of a spectator ion?
An ion which are present in the solution but do not take part in the reaction (ions that do not have a change of state or oxidation state)
What is the definition of an ionic precipitation reaction?
A reaction which produces a solid ppt. on mixing 2 solutions containing ions
What are the solubility rules?
NITRATES - All soluble
CHLORIDES - All soluble EXCEPT lead and silver
SULPHATES - All soluble EXCEPT lead, calcium and barium
POTASSIUM, AMMONIUM AND SODIUM SALTS - All soluble
CARBONATES - All insoluble EXCEPT PAS salts
HYDROXIDES/ OXIDES - All insoluble EXCEPT PAS salts
NB: calcium hydroxide is slightly soluble
Describe the set up and the variables for the practical: Investigating the Thermal Decomposition of Carbonates
INDEPENDANT VARIABLE: metal carbonate
DEPENDANT VARIABLE: time taken for the limewater to turn cloudy
CONTROL VARIABLES:
- distance between flame and test tube
- same moles of metal carbonate
- same volume and conc. of limewater
SET UP:
- Attach a test tube with you metal carbonate inside horizontally to a clamp with a bung
- Have a delivery tube going from the bung to a test tube filled with limewater
- Heat the metal carbonate using a bunsen burner and time how long it takes for the limewater to turn cloudy
- Repeat for all the metal carbonates in the group
What is the independent variable?
The variable that you change
What is the dependent variable?
The variable that you measure
What are the observations in the practical: Investigating the Thermal Decomposition of Carbonates
GROUP 2 CARBONATES (NOT THERMALLY STABLE)
- Bubbles are produced
- Limewater turns cloudy
- powder moves up beaker
GROUP 1 CARBONATES (THERMALLY STABLE
- does not react
What are the two ways that you can determine the time taken for the metal nitrate to decompose in the practical: Investigating the Thermal Decomposition of Nitrates
Test for Oxygen: Put a glowing splint into the test tube containing the unknown gas, if O2 is present then the splint will relight
Test for Nitrogen dioxide:
- Brown gas so can visually see
- NO2 is slightly acidic so should turn damp blue litmus paper red
