Mr. Tim's A-Level Chemistry Hub

Browse by level and unit

IG ChemistryPearson Edexcel International GCSE

Atomic Structure & Periodic Table2 simulations

Formulae, Mixtures & Quantitative Chemistry2 simulations

Bonding, Structure & Electrolysis3 simulations

Inorganic Chemistry2 simulations

Physical Chemistry4 simulations

Organic Chemistry & Materials3 simulations

AS ChemistryPearson Edexcel IAS · Grade 11

Atomic Structure & Amounts3 simulations

Bonding & Intermolecular Forces1 simulation

Energetics, Kinetics & Equilibria1 simulation

Inorganic & Redox ChemistryComing soon

Redox and the chemistry of Groups 1, 2 and 7.

Organic ChemistryComing soon

Alkanes, alkenes, alcohols and halogenoalkanes.

Analysis & Practical SkillsComing soon

Mass spectra, infrared spectra and practical methods.

A2 ChemistryPearson Edexcel IA2 · Grade 12

KineticsComing soon

Rate equations, orders and activation energy.

Thermodynamics & EquilibriumComing soon

Entropy, energetics and equilibrium constants.

Acids, Bases & BuffersComing soon

pH, buffers and titration curves.

Redox & Transition MetalsComing soon

Electrode potentials and transition-metal chemistry.

Advanced Organic Chemistry1 simulation

Analysis & Organic SynthesisComing soon

Spectroscopy, synthesis routes and practical analysis.

IGCSE · States of matter

What is the change of state?

Drag a state into each circle. The arrow reads from the first circle to the second.

On a phone or tablet, tap a state and then tap a circle.

Your result Choose two states to begin

The direction matters: solid → liquid is melting, but liquid → solid is freezing.

Solid: ordered Liquid: close, irregular Gas: far apart

IGCSE · Electrolysis and metal extraction

Extracting aluminium by electrolysis

Watch ions move through molten aluminium oxide dissolved in cryolite. The graphite lining is the negative cathode; the carbon blocks are positive anodes.

1Break crust & feed Al₂O₃
2Dissolve in cryolite
3Electrolyse at ≈960°C
4Form CO₂ & consume carbon
5Tap molten aluminium

Drag to rotate · scroll or pinch to zoom · right-drag to pan

Before electrolysis: the Bayer process purifies bauxite into alumina, Al₂O₃. Cryolite dissolves alumina and lowers the operating temperature to about 960°C. Cell polarity: the carbon lining is the cathode; suspended carbon blocks are the anodes. Overall: 2Al₂O₃ + 3C → 4Al + 3CO₂

K_p Simulator

N₂O₄ ⇌ 2 NO₂ · Endothermic (ΔH° = +57.2 kJ/mol)
Only temperature changes K_p. Changing pressure (volume) or concentration shifts the equilibrium position but the K_p calculation always gives the same answer.

N₂O₄ ⇌ 2 NO₂

🌡

Temperature changes K_p

298 K

📦

Volume K_p unchanged ✓

30.0 L

⚗

Initial N₂O₄ K_p unchanged ✓

1.00 mol

Equilibrium gas mixture — mole fraction (bar width) shifts with volume & concentration; Kp computed below stays constant

N₂O₄ colorless

NO₂ brown

Live K_p derivation — updates with every slider move

① Equilibrium concentrations (mol/L)

[N₂O₄]_eq = 0.0271 [NO₂]_eq = 0.0125

↓ P = [c] × RT (R = 0.08206 L·atm·mol⁻¹·K⁻¹, RT = 24.45 L·atm·mol⁻¹)

② Partial pressures (atm)

P(N₂O₄) = 0.0271 × 24.45 = 0.6621

P(NO₂) = 0.0125 × 24.45 = 0.3059

↓ K_p = P(NO₂)² / P(N₂O₄)

③ K_p (atm)

K_p = (0.3059)² / 0.6621 = 0.09357 / 0.6621 = 0.1414 atm ← only T can shift this

④ Verify via K_c

K_c = [NO₂]² / [N₂O₄] = 0.005782 mol/L → K_p = K_c × RT = 0.005782 × 24.45 = 0.1414 atm ✓

Equilibrium Constant

K_p = 0.1414

atm

temperature-dependent only

Partial Pressures at Equilibrium

N₂O₄

0.662 atm

NO₂

0.306 atm

P_total = 0.968 atm

Dissociation α

18.8%

of N₂O₄ converted to NO₂

Drag the sliders — only temperature changes K_p; volume and concentration just shift the equilibrium position.

Electron Orbital Viewer

Point cloud weighted by |ψ(r)|² — denser regions have higher electron probability.
Hydrogen atom s-orbitals (a₀ = 1). Drag to rotate · scroll to zoom.

drag to rotate · scroll to zoom

1s orbital — lowest-energy state, spherically symmetric. Electron density peaks at the nucleus and decays exponentially outward. No radial nodes.

Electron Configuration Builder

Add electrons one at a time · Aufbau principle · Hund's rule applied within each sublevel
Covers elements H → Zn (Z = 1–30) · 4s fills before 3d per Aufbau order

— Z = 0

0 / 30 electrons

Electron Configuration

—

Chromium & Copper: Aufbau Exceptions

Cr (Z=24) and Cu (Z=29) deviate from the Aufbau principle because half-filled and fully-filled d subshells are extra stable.

Chromium Z = 24

Group 6 · Period 4 · [Ar] core = 1s² 2s² 2p⁶ 3s² 3p⁶

Aufbau predicts

[Ar] 4s² 3d⁴

↑↓

↑

→

Actual

[Ar] 4s¹ 3d⁵

↑

⚡ The 3d subshell is half-filled (3d⁵ — one electron per orbital, all spin-up). This maximises exchange energy and minimises electron-electron repulsion, making 4s¹ 3d⁵ lower in energy than the predicted 4s² 3d⁴. One electron is effectively "promoted" from 4s into the empty 3d orbital.

Copper Z = 29

Group 11 · Period 4 · [Ar] core = 1s² 2s² 2p⁶ 3s² 3p⁶

Aufbau predicts

[Ar] 4s² 3d⁹

↑↓

↑

→

Actual

[Ar] 4s¹ 3d¹⁰

↑

↑↓

⚡ The 3d subshell is fully filled (3d¹⁰). A completely filled d subshell is particularly stable. The atom reaches it by promoting one 4s electron into the last 3d orbital, giving 4s¹ 3d¹⁰ instead of the predicted 4s² 3d⁹.

Key takeaway

Both exceptions involve a one-electron shift from 4s → 3d to achieve an especially stable d subshell (half-filled 3d⁵ for Cr, fully-filled 3d¹⁰ for Cu). The same pattern recurs across the periodic table: Mo (Z=42), Ag (Z=47), Au (Z=79), and others. These exceptions are a frequent exam topic in AP, IB, and university chemistry.

Interactive Atomic Model

Oxygen-16 · 8 protons · 8 neutrons · 8 electrons · click any particle to inspect it

8O15.999

Shell 12e⁻Shell 26e⁻

Drag to turn · click a particle · click empty space for element info

Atomic number8 Mass number16 Overall charge0 Shell arrangement2, 6 Electron configuration1s² 2s² 2p⁴

SN1 vs SN2 Rate Simulator

Compare how substrate structure, concentration, nucleophile and solvent change the relative reaction rate.

R–X + Nu⁻ → R–Nu + X⁻

Substrate structure Solvent Nucleophile [R–X] concentration 1.0 mol dm⁻³ [Nu⁻] concentration 1.0 mol dm⁻³

SN1rate = k[R–X]

The slow step forms a carbocation, so nucleophile concentration is absent from the rate law.

SN2rate = k[R–X][Nu⁻]

Substrate and nucleophile collide in one slow step, so both concentrations affect the rate.

SN1

0.12

SN2

0.20

Relative rate on a shared scale

SN1 · two stepsR–X → R⁺ + X⁻slowR⁺ + Nu → R–Nu

SN2 · one stepNu⁻ + R–X → [transition state] → R–Nu + X⁻concerted

Rates are relative teaching values, not experimental rate constants.

Interactive calculation tools

Chemistry Calculators

Choose a syllabus unit, enter your values, and see every step of the calculation.

A2 · 1 calculator

Unit Formulae & EquationsGuided balancing

Guided Equation Balancer

Enter each chemical separately, then adjust only the coefficients until every element has equal atom totals.

Your equation · 自选方程式

Enter your own balancing problem

Type each reactant and product into its own Chemical box. Keep every coefficient in the separate Coefficient box.

Or load a guided example:

1Enter chemicalsFormulae only—no large numbers
2Adjust coefficientsUse the number controls
3Check and improveCompare each atom total

Reactants 反应物

→reacts to form

Products 生成物

◎

Build the equation first

Choose an example or type chemical formulae into the boxes.

Formula tips: use normal numbers for subscripts, for example H2O, Ca(OH)2 or Al2(SO4)3. Do not type a coefficient inside the chemical box.

Unit Acids & Bases Buffers and pH

Calculated buffer pH 4.76

4.76 + log₁₀(0.20 ÷ 0.20) = 4.76

0 · acidic7 · neutral14 · alkaline

Base : acid ratio = 1.00

Equal concentrations mean pH = pK_a.

Use concentrations in the same units. This equation applies to a buffer made from a weak acid and its conjugate base.

Self-test · 自我测试

Chemistry Quiz

Choose your level. Difficult vocabulary includes short Chinese support without giving away the chemistry.

IGCSE · 20 topics · 200 questions

Edexcel International GCSE

Choose a topic to practise

Your topic scores stay on this device. Retake any set to receive shuffled questions and options.

Class code 班级代码（可选）

Teacher analytics

Results are saved on this device. Connect the optional Google Sheet endpoint to collect anonymous class-wide question data.

Interactive Periodic Table

Select any element to view its atomic data and electron configuration.

Find an element

Chemistry language · 化学词汇

Vocabulary List

Review essential English chemistry terms with Chinese translations and concise definitions.

Search vocabulary

IGCSE Chemistry

Teacher resource library

Teaching Slides & Materials

Download chemistry assessments, lesson materials and future teaching slides.

1 resource

Practice assessment

Chemistry Exam 1 - Form A

Seven-page chemistry assessment covering solution equilibria, acids, bases and related calculations.

7 pagesPDF656 KB

Open PDF Download

Official Pearson resources

IAL Chemistry Past Papers

June exam series with question papers and corresponding mark schemes. AS covers Units 1–3; A2 covers Units 4–6.

Full Pearson archive ↗

2025June series

AS · Units 1–3Question papers + mark schemes A2 · Units 4–6Question papers + mark schemes

2024June series

AS · Units 1–3Question papers + mark schemes A2 · Units 4–6Question papers + mark schemes

2023June series

AS · Units 1–3Question papers + mark schemes A2 · Units 4–6Question papers + mark schemes

Files open on Pearson’s official website. Pearson retains copyright and controls availability; recent locked materials require a registered-centre login.

Mr. Tim’s A-Level Chemistry Hub

What is the change of state?

Extracting aluminium by electrolysis

Chemistry Calculators

Guided Equation Balancer

Enter your own balancing problem

Reactants 反应物

Products 生成物

Henderson–Hasselbalch Calculator

Chemistry Quiz

Choose a topic to practise

Your result

A2 Chemistry question bank is coming next

Vocabulary List

Teaching Slides & Materials

Chemistry Exam 1 - Form A

IAL Chemistry Past Papers