Period 3 elements

Question 1

Elements in period 3

Answer 1

• Sodium, Na
• Magnesium, Mg
• Aluminium, Al
• Silicon, Si
• Phosphorus, P
• Sulfur, S
• Chlorine, Cl
• Argon, Ar

Question 2

Reaction of Sodium with water

Answer 2

• Sodium reacts vigorously with cold water because it doesn’t take much energy to lose one electron
• It forms a molten ball on the surface of the water, and produces hydrogen gas and NaOH
• The solution has a pH of 12-14, so is a strong alkali

Question 3

Reaction of Magnesium with water

Answer 3

• Magnesium reacts slowly with cold water as it takes lots of energy to lose two electrons.
• This reaction isn’t visible, but it produces hydrogen gas and Magnesium hydroxide (Mg(OH)2), which has a pH of 9-10, making the solution weakly alkaline
• It reacts much faster with steam, as it has more energy. This forms Magnesium oxide and hydrogen

Question 4

Reactions with oxygen

Answer 4

• Na2O, MgO and Al2O3 are all giant ionic structures
• SiO2 is giant covalent, P4O10 is simple covalent
• SO2 and SO3 are also simple covalent, SO2 is more common than SO3 as SO3 requires high pressure, temperature and a vanadium catalyst to form
• Al and Si are the only two that don’t react readily in air

Question 5

Flame test colours

Answer 5

• Sodium = yellow
• Magnesium = white
• Phosphorus = white
• Sulfur = blue

Question 6

Melting points of oxides

Answer 6

• The trend in melting points increases from Na2O to MgO because Mg is a 2+ ion and as such has a stronger attraction to the electrons than Na
• Al has covalent character which weakens the metallic bond so the trend decreases between MgO and Al2O3
• Giant covalent structure is weaker than giant ionic, so the trend decreases from Al2O3 to SiO2
• The trend decreases further from SiO2 to P4O10 and SiO2 as simple covalent molecules are held together by weak IMF, and P4O10 has stronger Van der Waals forces than SiO2 as it is a larger molecule
• Therefore the trend decreases overall across the group

Question 7

Metal oxides reacting with water

Answer 7

• Metallic oxides form alkaline solutions in water
• Na2O + H2O -> 2NaOH
• MgO + H2O -> Mg(OH)2
• Al2O3 amphtoteric, so it forms an acid and an alkali

Question 8

Non-Metal oxides reacting with water

Answer 8

• Non-metal oxides from acidic solutions
• SiO2 doesn’t dissolve in water
• P4O10 + 6H2O -> 4H3PO4
• SO2 + H2O -> H2SO3
• SO3 + H2O -> H2SO4
• when these acids react with a base it forms a salt and water