S Block Flashcards
Group 1 and 2 elements are know as s-block elements, why?
They all have outer electrons in the s subshell; ns^1 and ns^2
Group 1 metals like to ___ one outer electron
Group 2 metals like to ___ one outer electrons
Lose
Lose
Therefore m, groups 1 and 2 are what agents?
Since they become what when undertaking chemical reactions?
Powerful reducing agents
Oxidised
Group 1 and 2 metals easily behave this way, why?
Since their ionisation energies are low
What are the equations to show how group 1 and 2 metals are ionised?
Group 1:
M ————> M^+ + e^-
Group 2:
M^2+ ——-> M^2+ + 2e^-
Reaction groups 1 and 2 elements
What should you remember?
Remember that all reactions of groups 1 and 2 will demonstrate oxidation since they like to lose their outer electrons.
Reactions with oxygen:
Group 1
All very reactive metals
Have to be stored out of contact with air to prevent oxidation
Reactivity increases as you go down the group
Reactions with oxygen:
Group 1
Continued
What are the elements stored in?
Lithium, sodium and potassium are stored in oil. (Lithium in fact floats on the oil, but there will be enough oil coating it to give it some protection. It is, anyway, less reactive than the rest of the Group.)
Rubidium and caesium are normally stored in sealed glass tubes to prevent air getting at them. They are stored either in a vacuum or in an inert atmosphere of, say, argon.
The tubes are broken open when the metal is used.
Reactions with oxygen:
Group 2
Explain
Examples (Magnesium and calcium)
Summary
All the metals in group 2 react with oxygen, but with increasing ease down the group. They all form white oxides when heated in oxygen
Magnesium + oxygen
2Mg + O2 —> 2MgO
Calcium + oxygen
2Ca +2O —> 2CaO
Summary:
A metal + oxygen gives a metal oxide
Flame tests
Compounds containing the ion:
Lithium
Sodium
Potassium
Magnesium
Calcium
Strontium
Barium
Lithium - deep red
Sodium - yellow/orange
Potassium - lilac
Magnesium - colourless
Calcium - brick red
Strontium - crimson
Barium - apple green
Flame tests:
What can the colour test be used for?
To identify the element present as the colours are those of the compounds of group 1&2
Reactions with water:
Group 1
General observations
- All group 1 metals react vigorously or even explosively with cold water to produce colorless solutions. (All group 1 hydroxides are soluble)
- In each case, a solution of the metal hydroxide is produced together with hydrogen gas, which we see as fizzing and bubbling.
(What you observed because of hydrogen)
• Group 1 metals become more reactive towards water as we go down the Group.
Reactions with water:
Group 1
Equations
Sodium and potassium
Sodium and water
2Na + 2H2O —> 2NaOH + H2
Reactions with water:
Group 1
Metals and observations in water
Lithium
Sodium
Potassium
Lithium:
Fizzes and bubbles, moves around on surface of water
Sodium:
As above but also bursts into flame
Potassium: also bursts into flame with a much more explosive/violent reaction
Reactions with water:
Group
Briefly describe
Group 2 elements react less readily with water than group 1 elements.
However they react with increasing vigour on the descent of the group
Reactions with water:
Group 2
Metals and observations in water
Magnesium
Calcium
Strontium/barium
Magnesium:
Reacts vigorously only with steam
Reactions with water:
Group 2
Metals and observations in water
Calcium
It ___ in ___ water.
Reaction is ____.
Water turns ____ due to ____ of ____.
Calcium: calcium sinks in cold water. Reaction is vigorous. Water turns milky due to the low solubility of calcium hydroxide
Reactions with water:
Group 2
Metals and observations in water
Strontium/ barium:
Reacts more ___ than___. ___ in water. ___ solutions are produced since their hydroxides are ____ ___.
Strontium/ barium:
Reacts more vigorously than magnesium/ calcium. Sink in water. Colourless solutions are produced since their hydroxides are more soluble
Reactions with water:
Group 2
Metals and observations in water
Magnesium + water
Mg + 2H2O —> Mg(OH)2
Reactions with water:
Summary
If you add a group 2 metal and water you get metal hydroxide and hydrogen gas
Reactions with dilute acid:
Only require group 2
The elements _____ all react with _____ vigour with acids such as ___ and ____ on decent of the group
The elements Mg-Ba all react with increasing vigour with acids such as HCI and H2O4 on decent of the group
Reactions with dilute acid:
What are redox reactions?
The metal is oxidised form oxidation state zero to oxidation state (+2) whilst a corresponding reduction occurs.
Reactions with dilute acid:
Two examples of redox reactions
Magnesium and calcium
Magnesium + sulphuric acid
Mg + H2SO4 —> MgSO4 + H2
Slight PPT
Calcium + hydrochloric acid
Ca + 2HCl —> CaCl2 + H2
H must exist like H2
Reactions of Group 2 with OH^- SO4^2- CO3^2- ions (solubility trends):
With OH- ions
Write a balanced equation for
MgCl2(aq) + NaOH(aq) —>
MgCl2(aq) + 2NaOH(aq) —> Mg(OH)2 + 2NaCl
Reactions of Group 2 with OH^- SO4^2- CO3^2- ions (solubility trends):
With OH- ions
Precipitates (PTT) of:
Mg(OH)2
Ca(OH)2
Ba(OH)2
Mg(OH)2. White ppt
Ca(OH)2. V light ppt
Ba(OH)2. No ppt
Reactions of Group 2 with OH^- SO4^2- CO3^2- ions (solubility trends):
With OH- ions
Ionic equation;
from your equations, what can you deduce about the trend in solubility of the hydroxides in group 2
Solubility of group 2 hydroxides increases down the group
Remember that when we react group 2 metals with water we form metal hydroxides, this trend explains why the reaction between calcium and water produces a milky solution whilst the reaction between barium and water produces a colourless solution.
Reactions of Group 2 with OH^- SO4^2- CO3^2- ions (solubility trends):
With SO4^2- ions
Equation of MgCl2(aq)
