H2 Chemistry Notes: CORE IDEA 2, Topic 5 - The Periodic Table

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10 Feb 2025, 00:00 Z

Q: What does H2 Chemistry Notes: CORE IDEA 2, Topic 5 - The Periodic Table cover? A: Link periodic trends, Period 3 oxides/chlorides, and Group 2/17 reactivity to Core Idea 2 (The Periodic Table) requirements for the 2026 H2 Chemistry syllabus.

Periodic trends inform everything from bonding predictions to qualitative analysis.

This guide explains electron configuration roots of the trends, highlights compulsory case studies (Period 3 oxides and chlorides, Groups 2 and 17), and provides exam-ready examples.

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1 General Periodic Trends

Property	Across a period (left → right)	Down a group	Key reasoning
Atomic radius	Decreases	Increases	Effective nuclear charge vs shell number.
Ionisation energy	Increases (with small dips)	Decreases	Stronger nuclear attraction vs increased shielding.
Electronegativity	Increases	Decreases	Attraction for bonding electrons.
Metallic character

Oxide	Structure/Bonding	Acid-base behaviour	Reaction with water
\(\ce{Na2O}\)	Giant ionic	Basic	\(\ce{Na2O + H2O -> 2NaOH}\)
\(\ce{MgO}\)	Giant ionic	Basic (weaker due to lattice energy)	Slowly forms \(\ce{Mg(OH)2}\)
\(\ce{Al2O3}\)	Giant ionic with covalent character	Amphoteric	Reacts with acids and bases; insoluble in water.
\(\ce{SiO2}\)	Giant covalent	Acidic (weak)	Insoluble; reacts with strong bases on heating.
\(\ce{P4O10}\)	Molecular covalent	Acidic	\(\ce{P4O10 + 6H2O -> 4H3PO4}\)
\(\ce{SO2}\), \(\ce{SO3}\)	Molecular covalent	Acidic	Form \(\ce{H2SO3}\), \(\ce{H2SO4}\) respectively.

Chloride	Hydrolysis in water	Resulting solution
\(\ce{NaCl}\), \(\ce{MgCl2}\)	Dissociate without hydrolysis.	Neutral for \(\ce{NaCl}\); slightly acidic for \(\ce{MgCl2}\) due to hydrolysis of \(\ce{Mg^{2+}}\).
\(\ce{AlCl3}\)	Hydrolyses strongly.	Acidic, releases \(\ce{HCl}\).
\(\ce{SiCl4}\)	Violent hydrolysis.	Produces \(\ce{HCl}\) and solid \(\ce{SiO2}\).
\(\ce{PCl3}\), \(\ce{PCl5}\)	Hydrolyse to acids.	\(\ce{H3PO3}\) or \(\ce{H3PO4}\).
\(\ce{S2Cl2}\)	Complex hydrolysis.	Mixture of sulfur-containing acids.

Halide	Observation	Reason
\(\ce{Cl-}\)	Produces \(\ce{HCl}\) only.	Weak reducing agent.
\(\ce{Br-}\)	Produces \(\ce{SO2}\), \(\ce{Br2}\).	Moderate reducing strength.
\(\ce{I-}\)	Produces \(\ce{SO2}\), \(\ce{S}\), \(\ce{H2S}\), \(\ce{I2}\).	Strong reducing agent; further reduction.

H2 Chemistry Notes: CORE IDEA 2, Topic 5 - The Periodic Table

1 General Periodic Trends

2 Period 3 Oxides

3 Period 3 Chlorides

4 Group 2 (Alkaline Earth Metals)

4.1 Physical and Chemical Trends

4.2 Thermal Stability of Carbonates/Nitrates

4.3 Uses in Papers

5 Group 17 (Halogens)

5.1 Reactivity and Oxidising Strength

5.2 Disproportionation

5.3 Halide Reaction with H2SO4

6 Worked Example

7 Practical Angles

8 Common Misconceptions

9 Practice Drill

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