Properties of the period 3 elements Flashcards
Why does the melting point increase from Na+ to Al3+? (3)
The charge on the metal ion increases from Na+ to Al3+
The size of the metal ion decreases across the row
Therefore there is an increase in the strength of attraction between the metal ions and delocalised electrons
Why does silicon have the highest melting point? (3)
It has a macromolecular structure
With lots of covalent bonds
Which are very strong
Why do the non-metals in period 3 have low melting and boiling points? (3)
P4, S8 and Cl2 all have a simple molecular structure with Van der Waals intermolecular forces
Strength of the Van der Waals depends on the size of the molecule and S8 is largest, followed by P4 then Cl2
Argon exists as single atoms with the weakest Van der Waals out of all of them
Why does aluminium have the highest boiling point? (2)
Once silicon has been melted most of its strong covalent bonds have been broken, so boiling it requires only a little extra energy.
In the liquid state Aluminium still has strong electrostatic attraction between ions and delocalised electrons, and so still requires a large amount of energy to boil
Reaction of sodium with cold water:
- write the equation
- state the pH of the solution formed
2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
pH = 13-14
Reaction of magnesium with cold water:
- write the equation
- state the pH of the solution formed
Mg(s) + 2H2O(l) → Mg(OH)2(aq) + H2(g
pH = 9-10
Reaction of magnesium with steam:
- write the equation
- describe what you would observe
Mg(s) + H2O(g)→ MgO(s) + H2(g)
white flame
white solid
Reaction of chlorine with cold water:
- write the equation
- state the pH of the solution formed
Cl2(g) + H2O(l) —>—< HClO(aq) + HCl(aq)
pH = 2-3
Reaction of chlorine with cold water in the presence of bright sunlight:
- write the equation
- state the pH of the solution formed
2Cl2(g) + 2H2O(l) → 4HCl(aq) + O2(g
pH = 2-3
Reaction of sodium with oxygen to produce simple oxide and peroxide:
- write the equation
- flame colour
- precipitate colour
2Na(s) + ½O2(g) → Na2O(s)
Orange flame
2Na(s) + O2(g) → Na2O2 (s)
White solid
Reaction of magnesium with oxygen to produce simple oxide:
- write the equation
- flame colour
- precipitate colour
2Mg(s) + O2(g) → 2MgO(s)
Bright white flame
White solid
Reaction of aluminium with oxygen to produce simple oxide:
- write the equation
- flame colour
- precipitate colour
4Al(s) + 3O2(g) → 2Al2O3(s)
If you sprinkle aluminium powder you will get bright white flame/ sparkles
White solid
Reaction of silicon with oxygen to produce simple oxide:
- write the equation
- flame colour
- precipitate colour
Si(s) + O2(g) → SiO2(s)
Orange flame
Pure form of SiO2 is a white solid
Reaction of phosphorus with oxygen to produce simple oxide:
- write the equation
- flame colour
- precipitate colour
White P(v) P4(s) + 5O2(g) → P4O10(s)
White Phosphorous gives white flame
No ppt, White fumes produced
Reaction of sulfur with oxygen to produce simple oxide:
- write the equation
- flame colour
- precipitate colour
S(s) + O2(g) → SO2(s)
Pale blue flame
No ppt, Colourless gas
What is the trend in bonding across period 3? (1)
Across P3 the bonding changes from being Ionic on the left to covalent on the right
Why does MgO have the highest melting point of all the P3 oxides? (3)
MgO has ionic bonds.
There are strong electrostatic forces of attraction between oppositely charged ions.
These require a lot of energy to overcome
Why does Al2O3 have more covalent character then MgO? (3)
The Al3+ ion is smaller than the Mg2+ ion.
This means the Al3+ ion is more polarising than the Mg2+ ion.
This distorts the electron cloud around the O2- ion more so that there is more electron density shared between the two ions
For the oxides of Phosphorus and Sulphur, why does P4O10 have the highest melting point, followed by SO3 then SO2? (3)
These all have simple molecular structures.
They all have Van der Waals intermolecular forces between molecules.
P4O10 is the largest molecule so has the strongest Van der Waals, whereas SO2 is the smallest so has the weakest Van der Waals
Why does SiO2 have a high melting point? (3)
This has a macromolecular structure.
It has lots of covalent bonds.
Which are very strong.
Reaction of sodium oxide with water:
- write the equation
- state the pH of the solution formed
Na2O(s) + H2O(l) → 2Na+(aq) + 2-OH(aq)
pH = 13-14
Reaction of magnesium oxide with water:
- write the equation
- state the pH of the solution formed
MgO(s) + H2O(l) → Mg(OH)2(aq)
pH = 9-10
Explain why sodium oxide forms an alkaline solution when it reacts with water (2)
Sodium oxide contains O2– ions
These O2– ions react with water forming OH– ions
What is the pH of the solution when aluminium oxide or silicon dioxide are added to water?
7
Both insoluble in water and so undergo no reaction to make the water acidic or alkaline
