Structure of the Atom ആറ്റത്തിന്റെ ഘടന
The chapter opens in a computer lab. A group of students are looking at atom models (ആറ്റം മാതൃക) on a laptop. “There isn't just one model – there are many,” says one of them. Why did scientists keep changing their picture of the atom? In this chapter you will follow the story. Glowing discharge tubes (ഡിസ്ചാർജ് ട്യൂബ്) revealed the electron, and canal rays revealed the proton. Thomson pictured the atom as a plum pudding. Rutherford fired alpha particles at a thin gold foil and found a tiny nucleus. Bohr arranged the electrons in fixed shells (K, L, M, N), and Chadwick found the neutron. Then you will learn to use atomic number and mass number, write electron configurations such as 2, 8, 1 and draw shell diagrams. Finally you will meet isotopes and isobars, and see where they are used, from the cancer ward at RCC Thiruvananthapuram to the dating of ancient charcoal. This animated self-study guide starts from the basics: matter, charges and tiny numbers. It explains every idea step by step, answers every textbook question, and ends with a revision sheet and a model test.
The chapter in one picture
Left: three atom models (ആറ്റം മാതൃക) of the same atom, sodium, which has 11 protons (പ്രോട്ടോൺ), 12 neutrons (ന്യൂട്രോൺ) and 11 electrons (ഇലക്ട്രോൺ). In J. J. Thomson's plum pudding model (പ്ലം പുഡിങ് മാതൃക), electrons sit in a ball of positive charge. Rutherford's gold foil experiment showed that all the positive charge and almost all the mass are packed into a tiny nucleus (ന്യൂക്ലിയസ്), with the electrons revolving around it. Bohr then put the electrons in fixed orbits (ഓർബിറ്റ്) called shells (ഷെല്ലുകൾ): K, L, M. For sodium they hold 2, 8 and 1 electrons. (Not to scale: a real nucleus is about 10 000 to 100 000 times smaller than the atom.) Right: in a discharge tube (ഡിസ്ചാർജ് ട്യൂബ്) with air at low pressure (കുറഞ്ഞ മർദത്തിലുള്ള വായു), cathode rays (കാഥോഡ് രശ്മികൾ) travel from the cathode (−) to the anode (+). They pass through the hole in the anode and make a pale-green glow (ഇളംപച്ച നിറത്തിലുള്ള തിളക്കം) on the zinc-sulphide coating at the far end.
How to use this guide
🎬 Watch the animations
Rays leave cathodes, alpha particles bounce off a gold nucleus, and electrons jump between shells, one step at a time. Press Next ▶ or ▶▶ Auto play. Animations pause by themselves when you scroll away; click a lab to restart its clock.
🧪 Do the virtual experiments
Pump the air out of a discharge tube, bend cathode rays with plates and magnets, fire alpha particles at gold, and build atoms from protons, neutrons and electrons. Fill the shells of the first 20 elements and sort isotopes from isobars. Every lab follows the real science; where a picture cannot be to scale, the page says so.
✍️ Try before you see
Every question has a 💡 hint first and a ✅ final answer after. Work it out in your notebook, then check. The “Check yourself” quizzes at the end of each page tell you at once whether you are right.
📖 Textbook words
Purple മലയാളം words are the exact terms used in your textbook (pages 7–22), so you can match this guide with your book and write answers in either language.
🔇 Quiet and offline
The pages make no sound and need no internet: every page is a single file. Only the blue “🌐 Explore online” boxes link to websites. Use them only if you want to.
Learning path
Follow the pages in order. If you are already confident about atoms, molecules and symbols, positive and negative charge, and numbers like 1.6 × 10−19, you can skim pages 1–3. Still try their quizzes, because the chapter uses these ideas on every page.
Scientists in this chapter
Your textbook shows portraits of six scientists. Here they are as name cards, in the order of their main discoveries. You will meet each of them again in the chapter.
Also named in the textbook: Michael Faraday (studied electric discharges in gases at low pressure), Heinrich Geissler (1854 – Geissler tubes and better suction pumps), Julius Plücker (a glow that shifts in a magnetic field), Johann Wilhelm Hittorf (1869), Henri Becquerel (1896 – radioactivity), Robert Millikan (oil-drop experiment – the charge of the electron), and Hans Geiger and Ernest Marsden (Rutherford's partners in the gold foil experiment).
Quick glossary (Malayalam ↔ English)
| Textbook term | English | Meaning |
|---|---|---|
| ആറ്റത്തിന്റെ ഘടന | Structure of the atom | The chapter title: what an atom is made of and how its parts are arranged |
| ആറ്റം / ആറ്റങ്ങൾ | Atom / atoms | The tiny particles that elements are made of |
| ആറ്റം മാതൃക | Atom model | A scientist's picture of what the inside of an atom is like (Thomson, Rutherford, Bohr) |
| തന്മാത്ര | Molecule | The smallest particle of a substance that has all its properties and can exist independently |
| പദാർഥം | Substance | A kind of matter, such as sugar, water or iron |
| മൂലകം · ഘടക മൂലകങ്ങൾ | Element · constituent elements | A substance made of only one kind of atom · the elements that make up a compound |
| രാസസൂത്രം | Chemical formula | Symbols and small numbers that show the atoms in a molecule, e.g. H2O |
| ആറ്റങ്ങളുടെ എണ്ണത്തിന്റെ അനുപാതം | Ratio of the numbers of atoms | e.g. 2 : 1 for hydrogen and oxygen atoms in water |
| സബ്അറ്റോമിക കണങ്ങൾ | Subatomic particles | Particles smaller than the atom: electron, proton, neutron |
| ഇലക്ട്രോൺ · പ്രോട്ടോൺ · ന്യൂട്രോൺ | Electron · proton · neutron | Charge −1 (outside the nucleus) · charge +1 (in the nucleus) · no charge (in the nucleus) |
| ഡിസ്ചാർജ് ട്യൂബ് | Discharge tube | A glass tube with a gas at low pressure and an electrode at each end, used with a high voltage |
| ഇലക്ട്രോഡുകൾ | Electrodes | The metal plates through which electricity enters and leaves |
| കാഥോഡ് · ആനോഡ് | Cathode · anode | The electrode joined to the negative (−) terminal · the electrode joined to the positive (+) terminal |
| സുഷിരങ്ങളുള്ള (ആനോഡ് / കാഥോഡ്) | Perforated (anode / cathode) | An electrode with holes in it, so rays can pass through |
| കാഥോഡ് രശ്മികൾ | Cathode rays | Streams of electrons going from the cathode towards the anode |
| കനാൽ രശ്മികൾ / ആനോഡ് രശ്മികൾ | Canal rays / anode rays | Positive rays that pass through the holes of a perforated cathode (Goldstein) |
| വൈദ്യുതരോധി | Insulator | A material that does not let electricity flow, e.g. plastic, glass, air at normal pressure |
| ഉയർന്ന വോൾട്ടത | High voltage | A very strong electrical push – thousands of volts in a discharge tube |
| കുറഞ്ഞ മർദത്തിലുള്ള വായു | Air at low pressure | Thin air, after most of it has been pumped out |
| വൈദ്യുത ഡിസ്ചാർജ് | Electric discharge | Electricity passing through a gas, usually with a glow |
| നിർവാത പമ്പ് | Suction (vacuum) pump | A pump that removes air from a vessel |
| സിങ്ക് സൾഫൈഡ് (ZnS) · ഇളംപച്ച നിറത്തിലുള്ള തിളക്കം | Zinc sulphide · pale-green glow | A coating that glows when cathode rays strike it · the glow at the far end of the tube |
| അതാര്യ വസ്തു · നിഴൽ | Opaque object · shadow | An object rays cannot pass through · the dark patch behind it (cathode rays travel in straight lines) |
| നേർത്ത ഇതളുകളുള്ള ചക്രം | Paddle wheel | A light wheel that turns when cathode rays strike it (the particles have mass) |
| വൈദ്യുതമണ്ഡലം · കാന്തിക മണ്ഡലം | Electric field · magnetic field | The region between charged plates · the region around a magnet; both bend moving charges |
| ചാർജ് · മാസ് | Charge · mass | Positive, negative or none · the amount of matter in a particle |
| e/m അനുപാതം | e/m ratio | Charge ÷ mass of the electron = 1.76 × 1011 C/kg (Thomson) |
| ഓയിൽ ഡ്രോപ്പ് പരീക്ഷണം · കൂളോം (C) | Oil-drop experiment · coulomb | Millikan's experiment that measured the electron's charge, 1.6 × 10−19 C · the unit of charge |
| പ്ലം പുഡിങ് മാതൃക | Plum pudding model | Thomson's atom: a positive sphere with electrons embedded in it |
| റേഡിയോ ആക്ടീവത · വികിരണങ്ങൾ | Radioactivity · radiations | Some elements (uranium, thorium) give out radiations by themselves |
| ആൽഫ (α) · ബീറ്റ (β) · ഗാമ (γ) കിരണങ്ങൾ | Alpha · beta · gamma rays | Positive with mass · negative · no charge and no mass |
| ഗോൾഡ് ഫോയിൽ പരീക്ഷണം · സ്വർണ്ണത്തകിട് | Gold foil experiment · gold foil | Rutherford's experiment (1911): alpha particles fired at a very thin gold foil |
| ഫോട്ടോഗ്രാഫിക് ഫിലിം | Photographic film | The circular film that recorded where the alpha particles went |
| വ്യതിചലിക്കുക · വികർഷിക്കപ്പെടുക | Be deflected · be repelled | Turn away from the straight path · be pushed away (like charges repel) |
| ന്യൂക്ലിയസ് | Nucleus | The tiny central part of the atom: all the positive charge and almost all the mass |
| സൗരയൂഥ മാതൃക | Solar system model | Rutherford's model: electrons revolve round the nucleus like planets round the Sun |
| പരിമിതികൾ · സ്ഥിരത | Limitations · stability | What a model cannot explain · why the atom does not collapse |
| വൈദ്യുതകാന്തിക സിദ്ധാന്തം | Electromagnetic theory | The theory that says a revolving charge should keep losing energy |
| നിർവീര്യ കണങ്ങൾ | Neutral particles | Particles with no charge – Chadwick's neutrons (1932) |
| ബോർ ആറ്റം മാതൃക | Bohr atom model | Electrons revolve only in definite orbits, each with a definite energy (1913) |
| ഓർബിറ്റ് · ഷെല്ലുകൾ (K, L, M, N) | Orbit · shells | The fixed circular paths of the electrons, numbered 1, 2, 3, 4 … and named K, L, M, N … |
| ഊർജനിലകൾ · സ്ഥിരോർജനിലകൾ | Energy levels · stationary energy levels | Each orbit has a fixed energy; an electron's energy does not change while it stays in its orbit |
| ഊർജം ആഗിരണം ചെയ്യുന്നു · പുറത്തേക്ക് വിടുന്നു | Absorbs energy · emits energy | Jumping to a higher orbit takes in energy; falling to a lower orbit gives it out |
| യൂണിഫൈഡ് അറ്റോമിക് മാസ് യൂണിറ്റ് (u) | Unified atomic mass unit | The unit for the masses of atoms; a proton or neutron is about 1 u |
| മൗലിക കണങ്ങൾ · ക്വാർക്കുകൾ | Fundamental particles · quarks | Particles that cannot be divided further (the electron) · the three particles inside each proton and neutron |
| അറ്റോമിക നമ്പർ (Z) | Atomic number | Number of protons (= number of electrons in the atom); it decides the element |
| മാസ് നമ്പർ (A) | Mass number | Number of protons + number of neutrons, e.g. 3517Cl has A = 35 |
| പ്രതീകം | Symbol | One or two letters standing for an element, e.g. Na for sodium |
| ഇലക്ട്രോൺ വിന്യാസം | Electron configuration | The arrangement of electrons in the shells, written like 2, 8, 3 |
| ബാഹ്യ ഓർബിറ്റ് · ബാഹ്യതമ ഇലക്ട്രോണുകൾ | Outermost orbit · outermost electrons | The last shell that has electrons · the electrons in it (at most 8) |
| ഐസോടോപ്പുകൾ | Isotopes | Atoms of the same element with the same atomic number but different mass numbers |
| പ്രോട്ടിയം · ഡ്യൂറ്റീരിയം · ട്രിഷിയം | Protium · deuterium · tritium | The three isotopes of hydrogen: 0, 1 and 2 neutrons |
| രാസസ്വഭാവം · ഭൗതിക സ്വഭാവങ്ങൾ | Chemical properties · physical properties | Isotopes have the same chemical properties but slightly different physical properties |
| ഘനജലം · ആണവ നിലയങ്ങൾ | Heavy water · nuclear power stations | D2O, the oxide of deuterium · where it is used |
| ഫോസിലുകളുടെ കാലപ്പഴക്കം | Age of fossils | Found using carbon-14, a radioactive isotope of carbon |
| ഐസോബാറുകൾ · ഐസോടോണുകൾ | Isobars · isotones | Same mass number, different atomic numbers · same number of neutrons |
| വിലയിരുത്താം · തുടർപ്രവർത്തനങ്ങൾ | Let us assess · extended activities | The end-of-chapter questions and projects (solved on page 12) |
| സയൻസ് ഡയറി | Science diary | The notebook where you record your observations and diagrams |
🌐 Explore online (optional)
Everything in this guide works offline: each page is a single file with no internet needed. Some pages also have blue “🌐 Explore online” boxes. They link to free websites and interactive simulations, such as the PhET “Build an Atom” and “Rutherford Scattering” simulations. Those links need internet and open in a new tab. All of them are collected in the resources hub on page 13.
- 📄 Ernest Rutherford Science History Institute
Rutherford's life and work: a good starting point for the imaginary-interview activity. - 📄 The ABC's of Nuclear Science Lawrence Berkeley National Laboratory
A friendly guide to the nucleus, isotopes, radioactivity and alpha, beta and gamma rays. - 📄 Radiation Basics U.S. Nuclear Regulatory Commission
What radiation is, where it comes from and why people who work with it use shielding, distance and short times.
Made for self-learning. Works offline – every page is a single file. Study material prepared by Claude for Madhu's family study folder, October 2026.