[🧪] Periodicity/Period 3

Question 1

What is the general trend in

melting points in Period 3?

[🧪] Periodicity/Period 3

Answer 1

Across the period, melting point increases up till Si, then decreases after Si

metallic bonding → giant molecular → simple molecular

Question 2

What is the general trend in Period 3 for

electrical conductivity?

Answer 2

Across the period, electrical conductivity increases from Na to Al, then decreases after Al

Question 3

What is the general trend in Period 3 for

ionic radius?

Answer 3

Decreases from Na+ to Si4+, then increases significantly to P3-, then decreases from P3- to S2-

Question 4

Describe the visual observations when

sodium reacts with oxygen

Answer 4

• vigorous reaction
• bright yellow flame
• Na₂O formed (white solid)

Question 5

Describe what happens when

magnesium reacts with oxygen

Answer 5

• speed: vigorous reaction
• observations: burns with a bright white flame
• product: MgO (white solid)

Question 6

Describe the visual observations for when

powdered aluminium reacts with oxygen

Answer 6

• fast reaction
• bright white flame
• Al₂O₃ formed (white powder)

Question 7

Describe the visual observations for when

silicon reacts with oxygen

Answer 7

• speed: slow
• observations: bright white sparks
• product: SiO₂ (white powder)

Question 8

Conditions for the reaction between aluminium and oxygen

Answer 8

Powdered aluminium

Question 9

Conditions for the reaction between silicon and oxygen

Answer 9

Powdered silicon and strong heating

Question 10

Describe what happens when

phosphorus reacts with oxygen

Answer 10

• speed: vigorous reaction
• observations: yellow or white flame
• product: P₄O₁₀ (seen as white clouds)

Question 11

What is the product of phosphorous reacting with oxygen?

Answer 11

P₄O₁₀

Question 12

Describe the visual observations for when

sulfur reacts with oxygen

Answer 12

• gentle reaction
• blue flame

Question 13

Conditions for the reaction between sulfur and oxygen?

Answer 13

Powdered sulfur

Question 14

Speed of the reaction of sodium/magnesium/aluminium with chlorine gas

Answer 14

Vigorous

Question 15

Speed of the reaction of silicon/phosphorous with chlorine gas

Answer 15

Slow

Question 16

Conditions for the reaction between phosphorous and chlorine gas

Answer 16

Excess chlorine

Question 17

What happens when NaCl and MgCl₂ are put in water

Answer 17

• don’t react
• the polar water molecules are attracted to the ions and break down their giant ionic structures, dissolving them

Question 18

What happens when Al₂Cl₆ is put in water?

Answer 18

• broken down into Al3+ and Cl- ions, so the solid disappears
• Al3+ becomes hydrated, causing the water molecule bonded to it to lose an H+ ion, giving an acidic solution
• H+ and Cl- ions form HCl, given off as misty white fumes
• temperature increases

Question 19

Which Period 3 chlorides undergo a complete reaction with water?

Answer 19

SiCl₄ and PCl₅

Question 20

Describe the visual observations for when

SiCl₄ reacts with water

Answer 20

• HCl given off as white fumes
• SiO₂ formed (white precipitate)
• rapid reaction

Question 21

Describe the visual observations for when

PCl₅ reacts with water

Answer 21

rapid reaction

Question 22

How many molecules of HCl are given off when SiCl4 reacts with water?

Answer 22

4

Question 23

How many molecules of HCl are produced when PCl5 reacts with water?

Answer 23

5

Question 24

Trend of pH of solution formed when Period 3 chloride interacts with water

Answer 24

Across the period, the pH of the solution formed decreases when Period 3 chlorides interact with water

Question 25

What happens to the HCl produced by the reaction between PCl₅ and water?

Answer 25

The HCl, along with the H₃PO₄, dissociate in solution