period 3 Flashcards
Describe the structure of Na, Mg and Al
metallic. Positive metal ions surrounded by sea of delocalised electrons. Strong attraction between metal ions and electrons
How does the melting point change from Na to Al and why?
Na<Mg<Al
Mg2+ and Al3+ have higher charge density than Na+ as atoms get smaller and have more protons
So greater attraction between ions and electrons
What is the structure of Si and how does this affect its melting point?
Giant covalent lattice. Strong covalent bonds between silicon atoms. Takes lots of energy to overcome and break these bonds so very high MP
What is the structure of P4, S8 and Cl2?
Simple molecular. Covalent bonds in molecules but weak van de waals forces between molecules
How does the melting point change from P4 to Cl2 and why?
S8>P4>Cl2
S8 has the largest molecules and so biggest VdW forces (as more electrons) so higher melting point
What structure is Ar and how does this affect its melting point?
Simple molecular. Exists as single free, gaseous atoms- monatomic
Forms only very weak VdW forces so very low MP
How does atomic radius change across period 3?
Nuclear charge increases whilst shielding (as electrons in same main shell) stays the same so greater nuclear attraction and radius decreases
How does electronegativity change across the period?
Increases as smaller atomic radius and greater nuclear charge so stronger attraction between nucleus and pair of electrons in covalent bond.
How does Na react with water?
2Na + 2H2O –> 2NaOH + H2
floats, moves around, fizzes and melts
How does Mg react with water (l) and steam?
Mg + 2H2O –> Mg(OH)2 + H2 with water, slow and bubbles
Mg + H2O –> MgO + H2
burns with bright white flame and forms white solid
Hoe does Cl2 react with water?
Cl2 + H2O –> HCl + HOCl
disproportionation reaction
If indicator added will initially go colour for acid and then bleach due to OCl- ions
In bright light reacts further
How does Na react with oxygen?
4Na + O2 –> 2Na2O
Burns with yellow orange flame and produces white solid
Hoe does Mg react with oxygen?
2Mg + O2 –> 2MgO
Burns with bright white flame and produces white solid
How does Al react with oxygen?
4Al + 3O2 –> 2Al2O3
Difficult for foil to burn but powder burns more readily
Bright white light
white solid
How does silicon react with oxygen?
Si + O2 –> SiO2
Powder will burn
White solid and white flame
How does phosphorous react with oxygen?
P4 + 5O2 –> P4O10
Bright white flame
White smoke
Ignites very easily
How does sulfur react with oxygen?
S + O2 –> SO2
Burns with blue flame
Choking, toxic gas
So2 rather than SO3
Which period 3 oxides are covalent?
Na2O, MgO and Al2O3
How does the lattice enthalpy and covalent character change from Na2O to Al2O3?
Strength of ionic bonding increases as mrtal ions get smaller and more positive so magnitude of lattice enthalpy increases
Al2O3 has some covalent character as Al3+ is highly polarising
How do ionic oxides react with water?
Na2O = soluble
Na2O + H2O –> 2NaOH
pH 14
MgO = slightly soluble
MgO + H2O –> Mg(OH)2
pH 10
Al2O3 is insoluble
How do ionic oxides react with acid?
Na2O + 2H+ –> 2Na+ + H2O
MgO + 2H+ –> Mg2+ + H2O
Al2O3 + 6H+ –> 2Al3+ + 3H2O
How do ionic oxides react with strong alkali?
Na2O and MgO don’t react however Al2O3 does due to covalent character
Al2O3 + 2OH- + 7H2O –> 2 [Al(H2O)2(OH)4]-
What is the acid base nature of the metal oxide?
Na2O and MgO are basic
Al2O3 is amphoteric
Which oxides are molecular?
P4O10, SO2 and SO3
How do molecular oxides react with water?
P4O10 + 6H2O –> 4H3PO4
SO2 + H2O –> H2SO3
SO3 + H2O –> H2SO4
∂+ P/S is attacked by ∂- O so releases H+
How do molecular oxides react with acids?
Don’t as H+ doesn’t attack
How do molecular oxides react with alkalis?
Same reasons as with water
P4O10 + 12OH- –> 4PO4 3- + 6H2O
SO2 + 2OH- –> SO3 2- + H2O
SO3 + 2OH- –> SO4 2- + H2O
What is the acid base nature of molecular oxides?
Acidic as react with bases
Which oxides are covalent?
SiO2
How does it react with water and acids?
Doesn’t
With water because strong covalent bonds would need to be broken
How does SiO2 react with alkalis?
Difficult as giant covalent but does react with hot conc. alkali
SiO2 + 2OH- –> SiO3 2- + H2O
