[🧪] Periodicity/Period 3

Question 1

What is the general trend in Period 3 for

melting points?

Answer 1

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

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 is a white solid

Question 5

Describe visual observations when

Magnesium reacts with oxygen

Answer 5

• vigorous reaction
• burns with a bright white flame
• MgO is a white solid

Question 6

Describe the visual observations for when

powdered aluminium reacts with oxygen

Answer 6

• fast reaction
• bright white flame
• Al2O3 is a white powder

Question 7

Describe the visual observations for when

silicon reacts with oxygen

Answer 7

• slow reaction
• bright white sparks
• 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 the visual observations for when

phosphorus reacts with oxygen

Answer 10

• vigorous reaction
• yellow or white flame
• 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

Describe the reaction of sodium, magnesium and aluminium with chlorine gas

Answer 14

Vigorous

Question 15

Describe the reaction of silicon and 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

• white fumes given off
• SiO₂ is a 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