Scribd
Upload
53 views3 pages

Describe The Reactions of Period 3 Elements With Oxygen and Water Interpret The Ability of Elements To Act As Oxidising and Reducing Agents

1. The document discusses periodic table chapter 9.2 on reactions of period 3 elements with oxygen and water. It provides sample exam questions related to describing these reactions and identifying stronger reducing agents based on electronic structure. 2. Sodium and aluminium react with oxygen to form sodium oxide, sodium peroxide, and aluminum oxide respectively. Sodium and silicon react with water to form sodium hydroxide and hydrogen gas, with no reaction for silicon. 3. Of the options given, potassium is identified as the stronger reducing agent compared to sodium due to its larger size and lower effective nuclear charge making it easier to lose an electron. The chloride ion is also identified as a stronger reducing agent than the fluoride ion for

Uploaded by

Luk HK
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as DOCX, PDF, TXT or read online on Scribd
53 views3 pages

Describe The Reactions of Period 3 Elements With Oxygen and Water Interpret The Ability of Elements To Act As Oxidising and Reducing Agents

1. The document discusses periodic table chapter 9.2 on reactions of period 3 elements with oxygen and water. It provides sample exam questions related to describing these reactions and identifying stronger reducing agents based on electronic structure. 2. Sodium and aluminium react with oxygen to form sodium oxide, sodium peroxide, and aluminum oxide respectively. Sodium and silicon react with water to form sodium hydroxide and hydrogen gas, with no reaction for silicon. 3. Of the options given, potassium is identified as the stronger reducing agent compared to sodium due to its larger size and lower effective nuclear charge making it easier to lose an electron. The chloride ion is also identified as a stronger reducing agent than the fluoride ion for

Uploaded by

Luk HK
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as DOCX, PDF, TXT or read online on Scribd
You are on page 1/ 3

Chapter 9: PERIODIC TABLE

9.2 Reactions of Period 3 elements with oxygen and water

Candidates should be able to:


(a) describe the reactions of Period 3 elements with oxygen and water;
(b) interpret the ability of elements to act as oxidising and reducing agents

Question based on syllabus 9.2

1. Name the two elements of Period 3 which cannot react with oxygen gas under normal
conditions.

2. (a) Write the equations for the reactions between oxygen (if any) and
(i) sodium,
(ii) aluminium,
(c) sulphur.
(b) Describe the reaction in (a)(ii)

3. Write the equations for the reactions between water (if any) and
(a) sodium,
(b) silicon.

4. Which is a stronger reducing agent?


(Proton number Li, 3; Na, 11; Mg, 12; Cl, 17; F,9)
(a) sodium or potassium
(b) chloride ion or fluoride ion
(c) sodium or magnesium
Explain your answer in term of structure.
Question based on syllabus 9.2

1. Name the two elements of Period 3 which cannot react with oxygen gas under normal
conditions.

Chlorine, argon (Name it, not symbols)

2. (a) Write the equations for the reactions between oxygen (if any) and
(i) sodium,

2Na + O2  Na2O2
the answer in stpm level (small amount of sodium in excess of oxygen gas)

4Na + O2  2Na2O X * Not accepted in the recent stpm marking scheme.

(ii) aluminium,

4Al + 3O2  2Al2O3

(c) sulphur.

S + O2  SO2 or 2S + 3O2  2SO3

(b) Describe the reaction in (a)(ii)

Aluminium burns / reacts with oxygen (with a brilliant white flame) to form (white solid )
aluminum oxide.
 If more marks given, state the observations of the reaction, like brilliant white fumes,
yellow precipitate, bubble of gas etc…

3. Write the equations for the reactions between water (if any) and
(a) sodium,

2Na + 2H2O  2NaOH + H2

(b) silicon.

No reaction
4. Which is a stronger reducing agent? Explain your answer based on structure.
 Points depends on the marks given. More points are required if marks if higher.
 Answer based on structure (means size, proton number, effective nuclear charge etc)
NOT based on other things (like ionisation energy, standard reduction potential)

(a) Lithium or sodium (sodium or potassium)

Both are Group 1 elements with 1 valence electron / or electronic conf.


Potassium atom is larger than sodium atom
Nuclear charge of Potassium atom is larger than that of sodium atom,
But the increase of screening effect is much greater.
Thus, effective nuclear charge is smaller / nucleus attraction towards valence electron is
smaller
Potassium atom is easier to release the valence electron
K  K+ + e
Thus, potassium is a stronger reducing agent

 The original question compared Na and Li. If we simply based on structure, Na


is a stronger one (Na is more reactive than Li)
 However, if based on E value, Li is a stronger reducing agent (but Na is more
reactive). Why? You all can check from the internet. But, no need for your
STPM exam / not in the syllabus.
 So, to avoid the confusion, we better change the question to Na and K, then the
answer is K.

(b) chloride ion or fluoride ion

Both have 8 valence electrons / stable octet electronic configuration


Cl- ion is larger than F- ion
Nuclear charge of Cl- is larger than that of F- ion
But the screening effect is greater.
Thus, effective nuclear charge is smaller / nucleus attraction towards valence electron is
smaller
Cl- ion is easier to release one valence electron to form Cl atom
Cl-  Cl + e
Thus, Cl- ion is a stronger reducing agent compare to F- ion

(c) sodium or magnesium

Na has one, while Mg has two valence electrons (or electronic conf)
Both have the same screening effect,
But Na has a smaller nuclear charge and
Smaller effective nuclear charge / nucleus attraction towards valence electron is smaller
Sodium is easier to release the valence electron
Na  Na+ + e
Further more, more energy is required to remove two electrons compare to one.
Thus, sodium is a stronger reducing agent

You might also like