Periodicy Flashcards
Describe atomic radius across period 3.
Nuclear charge increases but shielding stays the same. Atomic radius decreases as the attraction between nucleus and outer electrons becomes greater.
Explain why magnesium has a greater melting point than sodium.
Magnesium has 2 delocalised electrons per atom whilst sodium only has 1 therefore the metallic bonding is stronger.
Explain why aluminium has a greater Melting point than magnesium.
Aluminium has 3 delocalised electrons per atom whereas magnesium only has 2 so the metallic bonding is greater.
Explain the trend in melting point of silicone and what causes this.
Higher melting point than expected.
Silicone is a giant covalent macromolecule so had 4 covalent bonds which must be broken.
Explain the trend In melting point of phosphorus.
Phosphorus is a simple covalent molecule which exists as P4. It has a very low melting point as only weak intermolcular van der waals forces must be overcome.
Explain the melting point of sulphur.
Sulphur exists as S8. Therefore there are more electrons that in P4 and more van der waals forces which must be overcome.
Explain the melting point of Cl.
Exists as a diatomic molecules with van der waals forces between atoms that must be overcome.
Explain the melting point of Ar.
Ar is a single monotomic has. However there are still van der waals forces between each atom which must be overcome.
Which element in period 3 has a lower boiling point than expected and why ?
Silicone.
Vaporisation occurs after the covalent bonds have been broken. Si2+ and Si3+ ions are formed.
Explain the conductivity of sodium.
Each sodium ions has 1 delocalised electrons capable of carrying charge.
Explain the conductivity of magnesium.
Each magnesium ion has 2 delocalised electrons capable of carrying the charger. Greater than sodium.
Explain the conductivity of aluminium.
Each ion has 3 delocalised electrons per ion capable of carrying charge.
Greater than sodium and magnesium.
Explain the conductivity of silicone.
Silicone has no delocalised electrons but is a giant covalent macromolecule which can become a semi-conductive metallic.
Lower than aluminium and magnesium.
Explain the conductivity of P, S, Cl, Ar.
No delocalised electrons so don’t conduct.
State the general trend in ionisation energies across period 3.
Increases
Nuclear charge increases but shielding stays the same. So there is a greater attraction between the nucleus and electrons meaning more energy is required to overcome this attraction.
Atomic radius decreases.
Explain the elements that derive from the general trend of first ionisation energies across period 3 and why.
Al - lower than expected. Electron is removed from the 3P orbital not the 3S which is a dumbbell shape and therefore further from the nucleus.
S- lower than expected. Electron pairs formed in the 3P orbital so the repulsion makes it easier for an electron to be removed.
Describe the trend in electronegativity across period 3.
Increases.
Greater nuclear charge
Same shielding
Decreasing atomic radius
Easier for nucleus to attract bonding pair of electrons in the covalent bond.
What is the formula for the reaction between sodium and water ?
2Na + 2H2O - 2NaOH + H2
Sodium hydroxide and hydrogen gas produced.
Why and where is sodium stored.
In liquid paraffin oil to prevent reaction with air.
What are the observations when sodium reacts with water.
Floats - less dense than water.
Moving around the surface of water to form sphere. The reaction is highly ectothermic so the surface of sodium is melted.
Effervescence as gas is given off.
Ph 13-14 produced.
What is the resultant Ph of the solution created when sodium reacts with water.
13-14
Write the equation for the reaction between magnesium and stream.
Mg(s) + H2O(g) - MgO(s) + H2(g)
What are the observations of the reactions of magnesium with water.
Effervescence as gas is given off.
White flame produced.
White magnesium oxide powder precipitate formed.
Ph 10
Write the equation for the reaction of chlorine with water.
Cl2(as) + H2O— HClO + HCl
Write the equation and state the observations for the reaction of oxygen with sodium.
4Na(s) + O2(g) - 2Na2O(s)
Yellow flame
White solid precipitate formed.
Write the equation and state the observations for the reaction of oxygen with magnesium
2Mg(s) + O2(g) - 2MgO(s)
White flame
White precipitate formed.