Curriculum
Integrated Science
Unit 1
0/5
1.1The Molecular Structure of Water, Its Unique Properties and Water Sustainability1.2The Atmosphere: Layers, the Greenhouse Effect and Ozone Depletion1.3Renewable Energy Sources, Green Hydrogen and Climate Adaptation1.4The Greenhouse Effect, the Carbon Footprint and Sustainable Solutions1.5Ecological Balance in Earth Systems, Biogeochemical Cycles and Food Webs
Unit 2
0/471.1Why study motion?1.2Definition of motion1.3Types of motion1.4Why we need velocity1.5Speed and velocity1.6Converting units1.7Worked examples1.8Uniform and non-uniform (variable) velocity1.9Instantaneous and average velocity1.10Worked examples1.11How to draw it1.12Reading the displacement–time graph1.13Worked examples1.14Definition1.15A motion diagram: the car that gains 5 m/s every second1.16Types of acceleration1.17Worked examples1.18Reading the graph1.19Analysing a multi-stage graph1.20Extension — displacement from the v–t graph1.21Motion (dot) diagrams1.22More worked examples1.23Short answers to typical discussion questions1.24Summary1.25Introduction1.26What is force?1.27Resultant force1.28Observation and the old belief1.29Statement of the law1.30Consequences of the first law1.31Inertia1.32Momentum1.33Statement1.34Another statement of the law1.35Definition of the newton1.36Thinking exercise1.37Worked examples1.38Life applications of the second law (force, time and change of momentum)1.39The first law as a special case of the second1.40Observations1.41Statement1.42Properties of action and reaction1.43Applications1.44Worked examples1.45Short answers to typical discussion questions1.46Summary1.47Key Scientific Tables & Anatomical Diagrams Extracted from Official Curricula
Unit 3
0/4
Text lesson
The Molecular Structure of Water, Its Unique Properties and Water Sustainability
The Molecular Structure of Water, Its Unique Properties and Water Sustainability
Overview
Overview
- Explain the bent structure of the water molecule and how hydrogen bonding produces its anomalous properties.
- Relate cohesion, adhesion, surface tension and capillarity to living systems.
- Interpret the density anomaly at 4 °C and its biological consequence in lakes and seas.
- Judge water quality from dissolved oxygen, pH and hardness, and discuss the sustainability of water resources.
🌳 Concept tree
Water→Structure, Properties and Sustainability
├── The molecule
- │ ├── O is sp3
- two lone pairs → bent shape
- bond angle 104.5°
│ ├── Polar covalent O–H bonds (ΔEN) → dipole
│ └── Hydrogen bonds→2 donated + 2 accepted per molecule
├── Bulk properties
- │ ├── Cohesion / adhesion → surface tension, capillarity
- │ ├── High specific heat capacity (4184 J/kg·°C) → climate buffering
- │ ├── High latent heat of vaporisation → evaporative cooling
- │ └── Universal solvent polar and ionic substances dissolve
├── The density anomaly
│ ├── Maximum density at 4 °C
- │ └── Ice is less dense → it floats → aquatic life survives winter
├── Water quality
- │ ├── pH 6.5–8.5 · dissolved oxygen · BOD · turbidity
- │ └── Hardness temporary (Ca(HCO₃)₂) vs permanent (CaSO₄, MgSO₄)
└── Sustainability
├── Virtual water and water footprint
- ├── Renewability of the water cycle vs aquifer mining
- └── Rational use, treatment, re-use and desalination
The Molecular Structure of Water, Its Unique Properties and Water Sustainability · 1 / 10
Scientific terms
Scientific terms
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| Polar molecule |
| partialnegativechargeside |
| Hydrogen bond |
| weakelectrostaticattractionbetween |
| Cohesion |
| attractionbetweenlikemolecules |
| Surface tension |
| energyneededincreasearea |
| Capillarity | the rise or fall of a liquid in a narrow tube caused by adhesion to the walls together with cohesion within the liquid | risefallliquidnarrow |
| Hardness |
| dissolvedcalciummagnesiumsalts |
| Dissolved oxygen (DO) |
| amountfreewatertypically |
| Biological oxygen demand (BOD) |
| neededmicroorganismsdecompose |
| Virtual water |
| embeddedproducedcommoditywheat |
The Molecular Structure of Water, Its Unique Properties and Water Sustainability · 2 / 10
Laws and quantitative relations
Laws and quantitative relations
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| Heat relation | Q = m·c·ΔT with cwater = 4184 J/(kg·°C) = 1 cal/(g·°C) — the highest specific heat of any common liquid. | cwater4184highestspecific |
| Latent heat of vaporisation |
| evaporationsweatremovesskin |
| Latent heat of fusion | 334 kJ/kg (80 cal/g) of ice | |
| Density |
| maximumthereforelighterfloats |
| Capillary rise |
| 2γcosθnarrowertubehigher |
| Water footprint |
| consumptioncapitayearbelow |
The Molecular Structure of Water, Its Unique Properties and Water Sustainability · 3 / 10
Molecular structure and hydrogen bonding
Molecular structure and hydrogen bonding
- Oxygen’s electron configuration is 1s2 2s2 2p4; it needs two electrons to complete its shell, so it shares them with two hydrogen atoms.
- The four electron pairs around oxygen are sp3 hybridised, but two of them are lone pairs, so the molecule is bent (V-shaped) with an H–O–H angle of 104.5°, not tetrahedral 109.5°.
- Oxygen (EN 3.5) attracts the shared electrons more strongly than hydrogen (EN 2.1), so oxygen carries a partial negative charge δ− and each hydrogen a partial positive charge δ+ — the molecule is a dipole.
- Each water molecule can form up to four hydrogen bonds with its neighbours: two through its hydrogen atoms and two through the lone pairs of oxygen.
- In the liquid the bonds break and reform about 1012 times a second; in ice the network is fixed and open, which is why ice is less dense.
- Hydrogen bonding also explains the anomalously high boiling points of the hydrides of group 16: H₂O (100 °C) far above H₂S (−60 °C), H₂Se and H₂Te.
Give the reason→water has a high boiling point and a high specific heat. Because energy is first consumed in breaking the network of hydrogen bonds between the molecules before they can separate or move faster.
The Molecular Structure of Water, Its Unique Properties and Water Sustainability · 4 / 10
Unique properties: solubility, surface tension and capillarity
Unique properties: solubility, surface tension and capillarity
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| Universal solvent for polar and ionic substances. |
| Watermoleculessurroundions |
| Cohesion and adhesion. | Hydrogen bonds hold water molecules together (cohesion) and to the walls of a xylem vessel or a glass tube (adhesion). Together they give high tensile strength to the water column | Hydrogenbondsholdwater |
| Surface tension |
| letsneedlefloatmakes |
| Capillarity |
| raiseswaterfinetubes |
| Thermal buffering. |
| Highspecificheatmoderates |
| Transparency |
| visiblelightletsalgae |
The Molecular Structure of Water, Its Unique Properties and Water Sustainability · 5 / 10
The density anomaly and its biological meaning
The density anomaly and its biological meaning
- Most substances contract continuously on cooling.
- Water contracts until 4 °C and then expands on further cooling because the open hydrogen-bonded lattice of ice holds the molecules farther apart than the liquid does.
- Consequence at 0 °C ice floats and forms an insulating lid on lakes and seas, so the water below stays near 4 °C and aquatic life survives the winter.
- In deep lakes in cold regions, water turns over twice a year because of this density maximum — spring and autumn overturn — which brings oxygen down and nutrients up.
- Without the anomaly, ice would sink, lakes would freeze from the bottom up and freshwater ecosystems would not exist in cold climates.
- Same principle applied water pipes burst, and rocks crack by frost shattering — a case of mechanical weathering.
The Molecular Structure of Water, Its Unique Properties and Water Sustainability · 6 / 10
Aquatic ecosystems, water quality and sustainability
Aquatic ecosystems, water quality and sustainability
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| • |
| lakeriverecosystemfood |
| • |
| Energymoveslosttrophic |
| Good-quality fresh water |
| aboveturbiditypathogeniccoliforms |
| Eutrophication |
| excessnitratesphosphatesfertilisers |
| Thermal pollution |
| powerstationslowerssolubility |
| Sustainable use |
| liningcanalspipesstop |
| The water–energy–food nexus |
| pumpingdesalinatingtreatingconsume |
The Molecular Structure of Water, Its Unique Properties and Water Sustainability · 7 / 10
Comparison tables
Comparison tables
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| Cohesion vs adhesion |
| likeunlikemoleculesresponsible |
| Temporary vs permanent hardness |
| HCO₃removableboilingdecomposes |
| Soft vs hard water |
| latherseasilysoapdangerous |
| Surface water vs groundwater |
| riverslakesreservoirsexposed |
| Distilled vs mineral water |
| puremineralsflattaste |
The Molecular Structure of Water, Its Unique Properties and Water Sustainability · 8 / 10
Worked examples
Worked examples
- How much heat raises 2 kg of water from 20 °C to 100 °C? — Q = 2 × 4184 × 80 = 669,440 J ≈ 669 kJ.
- How much steam is needed to cool a 70 kg athlete by 2 °C by sweating alone (assume no other loss)? — Q = 70 × 3500 × 2 ≈ 490 kJ (body tissue c ≈ 3500 J/kg·°C), mass of water = 490,000 / 2,400,000 ≈ 0.2 kg = 200 mL.
- A water sample gives an effervescence with dilute HCl and a white precipitate on boiling. Identify the hardness. — Temporary hardness due to calcium bicarbonate.
- A capillary of radius 0.2 mm is dipped in water (γ = 0.073 N/m, θ = 0°). Find the rise. — h = 2γ/(ρgr) = 2(0.073)/(1000 × 9.8 × 2×10−4) ≈ 7.4 cm.
- A family uses 0.25 m3 of water a day. Its annual volume, and how it compares with the water footprint of 1 kg of beef (about 15,000 L)? — 0.25 × 365 = 91 m3/yr, so one kilogram of beef costs about 5 months of the family’s domestic water.
The Molecular Structure of Water, Its Unique Properties and Water Sustainability · 9 / 10
Ministry exam traps
Ministry exam traps
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| 104.5°, not 109.5°. |
| lonepairspushbonding |
| Maximum density is at 4 °C, not at 0 °C. | Questions exchange the two temperatures | Questionsexchangetemperatures |
| Ice floating is a density argument |
| temperaturestatebecauseless |
| Water is not a universal solvent. | It dissolves polar and ionic substances only — non-polar fats are excluded | dissolvespolarionicsubstances |
| Hydrogen bonds are intermolecular |
| betweenmoleculescovalentinside |
| Temporary hardness is removed by boiling; permanent is not. | Reversing this is a classic objective error | Reversingclassicobjectiveerror |
| Eutrophication kills by oxygen depletion | not because the algae are poisonous — the damage is done by the decomposing bacteria | becausealgaepoisonousdamage |
The Molecular Structure of Water, Its Unique Properties and Water Sustainability · 10 / 10
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