Period 3 Flashcards
Trend in atomic radius across period 3
- increase in nuclear charge
- same shielding
- decrease in atomic radius
Trend in electronegativity across period 3
- increase in nuclear charge
- same shielding
- elements more capable of withdrawing electron density from covalent bond
Trend in 1st ionisation energy across period 3
- increase in nuclear charge
- same shielding
- greater attraction between outer electrons and positive nucleus
- requires more energy to be removed
Why does Al have a lower 1st IE than Mg?
- Al electron removed from 3p sub shell
- Mg electron removed from 3s sub shell
- 3p higher in energy than 3s
- so less energy required to remove electron
Why does S have lower 1st IE than P?
- S electron removed from 3p paired orbital
- P electron removed from 3p unpaired orbital
- S has lower 1st IE due to electron pair repulsion
Why does melting point increase from Na to Al?
- charge of metal ion increases
- size of metal ion decreases
- increase in strength of attraction between metal ions and delocalised electrons
Why does silicon have the highest melting point?
- Macromolecular
- with strong covalent bonds
- more energy needed to overcome
Why does S8 have higher MP/BP than P4?
- s8 bigger molecule
- stronger VDW
Why does P4 have higher MP/BP than Cl2?
- P4 bigger molecule
- stronger VDW
Why does Cl2 have higher MP/BP than Ar?
- Cl2 bigger molecule
- stronger VDW
- Ar only one atom - weaker VDW
Why does Al have the highest boiling point?
- once Si melted only a little more energy needed to overcome strong covalent bonds
- Al has strong electrostatic forces of attraction between positive ions and delocalised electrons in liquid state
Reaction of Na with cold water and pH
Na (s) + H2O (l) —> NaOH (aq) + H2 (g)
pH 13-14
What happens when Na reacts with cold water?
- effervescence
- metal melts
- strong alkali solution formed
Reaction of Mg with cold water and pH
Mg (s) + H2O (l) —> Mg(OH)2 (aq) + H2
pH 9-10
What happens when Mg reacts with cold water?
- slow reaction at room temp
- few bubbles of gas produced
- weak alkali formed
- as Mg(OH)2 sparingly soluble
Reaction of Mg with steam
Mg (s) + H2O (g) —>. MgO (s) + H2 (g)
2 reactions of Cl with cold water and pH
Reaction 1:
Cl2 (g) + H2O (l) —> HClO (aq) + HCl (aq)
Reaction 2:
Cl2 (g) + H2O (l) —> 4HCl (aq) + O2 (g)
Both pH 2-3
Silicon(IV) oxide is insoluble in water.
Explain, using an equation, why silicon(IV) oxide is classified as an acidic oxide.
- Reacts with alkalis
- SiO2 + 2NaOH —> Na2SiO3 + H2O
Explain why Mg has higher MP than Na+
- Mg2+ has greater charge than Na+
- stronger electrostatic forces of attraction between Mg2+ and delocalised electrons
State structure and bonding of silicon dioxide. Give 2 physical properties apart from high MP
Structure: Macromolecular
Bonding: Covalent
Physical properties:
Hard/brittle/non-conductor/insoluble
Give the formula of the species in a sample of solid phosphorus(V) oxide.
State the structure of, and describe fully the bonding in, this oxide.
Formula: P4 O10
Structure: simple molecular
Bonding: covalent and VDW between molecules
Sulfur(IV) oxide reacts with water to form a solution containing ions.
Write an equation for this reaction
SO2 + H2O → 2H+ + SO3 2-
OR
SO2 + H2O → H+ + HSO3 -
Write an equation for the reaction between the acidic oxide, phosphorus(V) oxide, and the basic oxide, magnesium oxide.
P4O10 + 6MgO → 2Mg3(PO4)2
OR
P4O10 + 6MgO → 6Mg2+ + 4PO43-
State the type of bonding in magnesium oxide.
Outline a simple experiment to demonstrate that magnesium oxide has this type of bonding.
- MgO is ionic
- melt it
- molten oxides conduct electricity
By reference to the structure of, and the bonding in, silicon dioxide, suggest why it is insoluble in water
- structure: macromolecular
- bonding: covalent
- water cannot break covalent bonds so it is insoluble
State how the melting point of phosphorus(V) oxide compares with that of silicon dioxide. Explain your answer in terms of the structure of, and the bonding in, phosphorus(V) oxide.
Melting point in comparison to phosphorus(V) oxide
- p4 O 10 is lower
- simple molecular substance
- covalent bonding
- weak VDW between molecules (easily broken)
Write an equation for a reaction that shows magnesium oxide acting as a base with another reagent.
MgO + 2HCl → MgCl2 + H2O
Phosphorus(V) oxide is classified as an acidic oxide.
Write an equation for its reaction with sodium hydroxide.
P4O10 + 12NaOH → 4Na3PO4 + 6H2O
Explain, in terms of structure and bonding, why sodium oxide has a high melting point.
- ionic
- strong electrostatic forces of attraction between ions
Explain, in terms of structure and bonding, why sulfur trioxide has a higher melting point than sulfur dioxide.
- SO3 larger molecule
- stronger VDW
Some Period 3 oxides have basic properties.
State the type of bonding in these basic oxides.
Explain why this type of bonding causes these oxides to have basic properties.
- ionic
- contains O2- ions
- O2- ions accept protons to form OH- ions
Sulfur dioxide reacts with water to form a weakly acidic solution.
Ions are formed when sulfur dioxide reacts with water.
Write an equation for this reaction.
SO2 + H2O → H+ + HSO3−
OR
SO2 + H2O —> 2H+ + SO3 2-
Sulfur dioxide reacts with water to form a weakly acidic solution. Ions are formed when sulfur dioxide reacts with water.
Write an equation for this reaction
Reaction is an equilibrium
Suggest why silicon dioxide is described as an acidic oxide even though it is insoluble in water.
SiO2 reacts with bases
Explain why the use of an excess of sodium hydroxide to neutralise the phosphoric(V) acid solution might lead to environmental problems in the lake.
An excess of NaOH would make the lake alkaline/toxic
Explain why an excess of magnesium oxide can be used for this neutralisation.
MgO is sparingly soluble
Write an equation for the reaction between phosphoric(V) acid and magnesium oxide.
3MgO + 2H3PO4 → Mg3(PO4)2 + 3H2O
OR
MgO + 2H3PO4 → Mg(H2PO4)2 + H2O
OR
MgO + H3PO4 → MgHPO4 + H2O
Write an equation for the reaction of P4O10 with water to form phosphoric(V) acid.
Give the approximate pH of the final solution.
P4O10 + 6H2O ⟶ 4H3PO4
pH 1-2
Explain why phosphorus(V) oxide has a higher melting point than sulfur(VI) oxide
- p4 O 10 bigger molecule
- stronger VDW
Phosphorus(V) oxide is known as phosphorus pentoxide.
Suggest why it is usually represented by P4O10 rather than by P2O5
exists as p4 O 10
Suggest why white phosphorus is stored under water.
prevents it reacting with air/oxygen
State the meaning of the term periodicity.
repeating pattern of physical and chemical properties
When a piece of sodium is added to 200 cm3 of water in a large beaker a vigorous reaction occurs. The temperature of the water increases by 25 oC
Give an equation, including state symbols, for the reaction of sodium with water. Suggest why it is dangerous to react a similar piece of sodium with 10 cm3 of water in
a boiling tube.
2 Na(s) + 2 H2O(l) → 2 NaOH(aq) + H2(g)
Temperature will go up more or reactants can shoot out of the tube
Give an equation and two observations made for the reaction that occurs when sodium is heated in oxygen.
4Na + O2 → 2Na2O
- white solid
- orange/yellow flame
Give an equation and one observation made for the reaction that occurs when phosphorus is heated in oxygen.
4P + 5O2 → P4O10
- bright white flame
Explain the increase in melting point from sodium oxide to magnesium oxide.
- Mg2+ greater charge
- stronger electrostatic forces of attraction between oppositely charged ions
Explain why the melting point of the oxide of silicon is much higher than that of the highest oxide of phosphorus.
- SiO2 = macromolecular
- p4O10 = simple molecular
- strong covalent bonds in SiO2 much stronger than weak VDW between molecules in P4O10
identify period 3 element with highest SECOND ionisation energy
sodium
explain why atomic radius decreases across period 3
- The number of protons increases OR nuclear charge increases
- Shielding is similar
Identify the element in Period 3, from sodium to chlorine, that has the highest electronegativity.
chlorine
