Chapter 3 · ApplicationsChemical bonds at home

Applications & Explore Online രാസബന്ധനം

The bonds of this chapter are all around a Kerala home. The salt from the salt pans, the ORS packet in the medicine box, the kerosene that takes grease off a shirt, the coconut oil that will not mix with water, the ice cube floating in a glass of lime juice, the fertiliser bag in the coconut garden and the white flash of burning magnesium in the school lab: each one is explained by transfer or sharing of electrons. Every section has a small animation and a sample exam question. The page ends with a hub of links to explore online.

📖 The ideas behind every section

Parts marked go further are beyond the textbook. Enjoy them, but for the exam stick to the textbook ideas. The animations are simplified.

🧂 Salt pansionic crystals, ORS ⚡ Wet handsions carry current 🛢️ Kerosenecovalent fuels, grease 🥥 Oil and waterpolar solvent 🧊 Floating icehydrogen bonds 🏷️ Labelsformulae of salts ✨ Magnesium flashtransfer of electrons

1. Common salt from the salt pans, and the ORS packet

Along the coast, sea water is let into shallow salt pans and left in the sun. The water evaporates, and white crystals of common salt, sodium chloride (NaCl), are left behind. Each crystal is a huge, regular stack of Na⁺ and Cl⁻ ions held together by ionic bonds അയോണിക ബന്ധനം. Strong attraction between the ions in every direction is why the crystals are hard and melt only at a very high temperature (about 801 °C go further). Salt dissolves easily in water, a polar solvent പോളാർ ലായകങ്ങൾ. That is why the ORS (oral rehydration solution) packet given for diarrhoea or heavy sweating can be stirred into a glass of clean water: its salt (with a little sugar) dissolves completely, and the sodium and chloride ions go back into the body.

☀️ Let the sun make salt
As the water evaporates, Na⁺ and Cl⁻ ions lock into a regular pattern: an ionic crystal.
📝 In the exam this looks like… “Common salt is obtained from sea water in salt pans. (a) Which type of chemical bond is present in sodium chloride? (b) Give two properties of common salt that show this.”
(a) Ionic bond: Na (2, 8, 1) gives 1 electron to Cl (2, 8, 7), forming Na⁺ and Cl⁻, which attract each other. (b) Any two: it is a crystalline solid; it is hard and non-volatile; it has a very high melting point; it dissolves in water (a polar solvent); its solution conducts electricity.

2. Why salt water conducts, and why wet hands near a switch are dangerous

Pure (distilled) water hardly conducts electricity, because it has almost no ions. Tap water, well water, rain on dirty skin and especially sweat have salts dissolved in them, so they contain free ions that can carry an electric current. That is exactly what you saw with the salt solution in the conductivity experiment (page 12). A wet hand on a switch or a wet plug therefore gives the current an easy path into your body.

💡 Bridge the gap and watch the lamp
Salt water: free Na⁺ and Cl⁻ ions move and carry the current. The lamp glows.
📝 In the exam this looks like… “We are told never to touch electrical switches with wet hands. Explain why, using what you learnt about ionic compounds.”
Water on our hands (sweat, tap water) contains dissolved salts, which are ionic compounds. In solution they give free ions, and ionic compounds conduct electricity in solution. So a wet hand lets current pass into the body, which can cause a dangerous electric shock.
⚠ Mains electricity (230 V) can kill. Never touch switches, plugs or wires with wet hands, never use electrical appliances near a bucket or tap, and never put anything into a socket. Do conductivity experiments only with low-voltage dry cells.

3. Covalent fuels, and kerosene that lifts a grease stain

LPG in the kitchen cylinder, petrol, diesel, kerosene മണ്ണെണ്ണ and candle wax are all covalent compounds സഹസംയോജക സംയുക്തങ്ങൾ of carbon and hydrogen. Just as the textbook says, they are gases, liquids or soft solids; they have low melting and boiling points (petrol and kerosene evaporate easily); they do not conduct electricity; and they do not mix with water. Grease and oil on a shirt or a bicycle chain are covalent too, so water cannot remove them, but kerosene, an organic solvent ഓർഗാനിക് ലായകങ്ങൾ, dissolves them.

🧺 Try to remove the grease stain
Kerosene and grease are both covalent; the grease dissolves in kerosene and the stain fades.
📝 In the exam this looks like… “A grease stain on a shirt does not come off with water but comes off with kerosene. Give the reason.”
Grease is a covalent compound. Covalent compounds are generally insoluble in water but soluble in organic solvents such as kerosene, carbon tetrachloride and benzene. So the grease dissolves in kerosene and is washed away.
⚠ Kerosene, petrol and LPG catch fire easily and their vapour is harmful to breathe. Use kerosene for stains only with an adult, outdoors or near an open window, far from any flame or lamp, and wash your hands afterwards.

4. Why water dissolves salt and sugar, but not coconut oil

Stir a spoon of salt, a spoon of sugar and a spoon of coconut oil into three glasses of water. The salt and the sugar disappear; the oil floats as a yellow layer on top. Water is a polar molecule പോളാർ തന്മാത്രകൾ: its oxygen end is slightly negative (δ−) and its hydrogen ends are slightly positive (δ+). The δ− oxygen ends crowd round each Na⁺ ion and the δ+ hydrogen ends round each Cl⁻ ion, pulling the ions out of the crystal. Ionic salt therefore dissolves in this polar solvent. Coconut oil is covalent and non-polar, so water molecules do not attract it; it dissolves in kerosene instead.

🥄 Stir three glasses
Salt: dissolves (ions). Sugar: dissolves (molecules). Coconut oil: does not dissolve; it floats as a layer.

Sugar is covalent, yet it dissolves in water. Its molecules have many O–H groups, which form hydrogen bonds with water. go further

📝 In the exam this looks like… “Common salt dissolves in water but not in kerosene. Coconut oil dissolves in kerosene but not in water. Explain.”
Common salt is an ionic compound; ionic compounds are soluble in polar solvents like water, whose δ− and δ+ ends attract the ions. Coconut oil is a covalent compound; covalent compounds are generally insoluble in water but soluble in organic solvents like kerosene.

5. Hydrogen bonds: floating ice and the high boiling point of water

A water molecule is small (H₂O, molecular mass only 18), yet water is a liquid at room temperature and boils only at 100 °C. The reason is the hydrogen bond ഹൈഡ്രജൻ ബന്ധനം: the δ+ hydrogen of one molecule is attracted by the δ− oxygen of the next. These attractions between molecules, intermolecular forces അന്തർതന്മാത്രാബലങ്ങൾ, hold the molecules together, so extra heat is needed to pull them apart. When water freezes, the hydrogen bonds lock the molecules into an open pattern of rings with empty spaces. The same mass of ice takes up more room than liquid water, so ice is less dense and floats. In a pond the ice stays on top, and the fish live on in the water below.

🧊 Freeze and melt
Ice: hydrogen bonds hold the molecules in open rings with spaces inside, so ice is less dense than water and floats.
📝 In the exam this looks like… “Ice floats on water. Water is a liquid at room temperature although its molecules are very small. Which force explains both facts? Explain.”
Hydrogen bonding. In water, H is covalently bonded to the highly electronegative O, so H gets δ+ and is attracted by the δ− O of a neighbouring molecule. These hydrogen bonds hold water molecules together, so water stays liquid at room temperature. In ice they hold the molecules in an open arrangement with empty spaces, so ice is less dense than water and floats.

6. Formulae on everyday labels

Read the labels in the kitchen, the medicine box and the coconut garden. Each salt name tells you two ions, and the formula comes from crossing over their charges, exactly as on page 10. Chalk and limestone are calcium carbonate; Epsom salt for sore feet is magnesium sulphate; fertilisers for coconut palms and paddy carry ammonium sulphate and ammonium phosphate.

🏷️ Pick a label, build its formula
📝 In the exam this looks like… “Write the chemical formulae of (a) ammonium phosphate (ions NH₄⁺ and PO₄³⁻) and (b) calcium carbonate (ions Ca²⁺ and CO₃²⁻).”
(a) Charges 1 and 3, cross over: (NH₄)₃(PO₄)₁ → (NH₄)₃PO₄. The bracket is needed because three NH₄ radicals are taken. Check: 3 × (+1) + (−3) = 0. (b) Charges 2 and 2: Ca₂(CO₃)₂ → divide by 2 → CaCO₃. Check: (+2) + (−2) = 0.

7. The white flash of burning magnesium

In the school lab your teacher may hold a strip of magnesium ribbon in tongs and touch it to a flame. It burns with a dazzling white light and leaves a white powder, magnesium oxide: 2Mg + O₂ → 2MgO. Each magnesium atom (2, 8, 2) transfers 2 electrons to an oxygen atom (2, 6), forming Mg²⁺ and O²⁻ ions held by an ionic bond. That bright light was used in the flash powder and flash bulbs of old cameras, and magnesium is still used for the white sparkles in fireworks and in emergency flares. go further

✨ Light the ribbon (teacher demonstration)
2Mg + O₂ → 2MgO: magnesium gives 2 electrons to oxygen, forming Mg²⁺ and O²⁻.
📝 In the exam this looks like… “Magnesium ribbon burns in air with a bright light to form a white powder. (a) Name the powder and write the equation. (b) Show the formation of its bond with an electron dot diagram.”
(a) Magnesium oxide; 2Mg + O₂ → 2MgO. (b) Mg with 2 crosses + O with 6 dots → [Mg]²⁺ [O (6 dots + 2 crosses)]²⁻; configurations Mg²⁺ (2, 8) and O²⁻ (2, 8). The bond is ionic.
⚠ Burning magnesium is a teacher demonstration only. Never look straight at the flame: its light is bright enough to hurt your eyes. Hold the ribbon in tongs over a heat-proof mat, keep water away from burning metal, and handle fireworks only with an adult, at a safe distance.
🔑 One idea, many uses

Transfer → ions → hard crystals, high melting points, dissolve in water, conduct in solution (salt, ORS, wet hands, MgO). Sharing → molecules, low boiling points, no conduction, dissolve in kerosene (fuels, grease, oil). Polar water + hydrogen bonds → universal solvent, floating ice.

🌐 Explore online – resources hub

Everything in this guide works offline. The links below are extras: simulations and articles from trusted sources (PhET, the Nobel Prize, Wikipedia, MolView and others), grouped by topic. They need internet and open in a new tab, so you will not lose your place here. Ask a parent or teacher before you go online. The PhET simulations Build a Molecule, Molecule Polarity and Molecule Shapes run directly in the browser, with nothing to install. The textbook suggests the program Ghemical for building molecules; MolView and Avogadro do the same job.

Octet rule and chemical bonds

🌐 Octet rule and chemical bonds needs internet · opens in a new tab

Ionic bonding

🌐 Ionic bonding needs internet · opens in a new tab

Covalent bonding and electron dot diagrams

🌐 Covalent bonding and electron dot diagrams needs internet · opens in a new tab

Electronegativity, polarity and hydrogen bonds

🌐 Electronegativity, polarity and hydrogen bonds needs internet · opens in a new tab

Valency and chemical formulae

🌐 Valency and chemical formulae needs internet · opens in a new tab

Build molecules yourself

🌐 Build molecules yourself needs internet · opens in a new tab
🧭 Next

Now pull the whole chapter together: Summary & Quick Quiz ▶