Atoms, Molecules and Reading Formulae തന്മാത്ര
The chapter opens at a school science exhibition. The students stare at pictures of molecules in which the atoms are strung together like beads on a necklace (മാലയിലെ മുത്തുകൾപോലെ). What holds those beads together? That question is the whole chapter. Before you can answer it, you need a few basic tools. You need to tell an element from a compound, read a chemical formula and count the atoms in it, know which molecules have one, two or many atoms, and know which elements are metals and which are non-metals. This page builds those tools from zero and fills in Tables 3.1 and 3.2 of your textbook.
- Nothing from earlier chapters – every idea is built up here.
- If you know elements, symbols and formulae well, do the two tables and the quiz, then move on to page 2.
1. Atoms held together like beads
പദാർഥങ്ങളിലെ ഘടക കണങ്ങൾ തമ്മിലുള്ള ആകർഷണബലമാണ് അവയെ ചേർത്തു നിർത്തുന്നത്. – It is the force of attraction (ആകർഷണബലം) between the constituent particles (ഘടക കണങ്ങൾ) of a substance that holds them together.
Everything around you, and your own body, is made of tiny particles called atoms (ആറ്റം). Usually atoms do not float about alone. They join into groups called molecules (തന്മാത്ര). A molecule is the smallest particle of a substance that can exist on its own and still has the properties of that substance. A water molecule, for example, is one oxygen atom joined to two hydrogen atoms.
A necklace (മാല) stays together because a thread runs through the beads. In a molecule there is no thread. The atoms are held by a force of attraction between them, and this force is called the chemical bond (രാസബന്ധനം). This chapter is about how such bonds form and why.
The balls are a code: real atoms have no colours, and the sticks only show which atoms are joined. Pull the atoms apart and let go: the force of attraction pulls them back. Breaking a bond needs energy. The double and triple sticks in O₂, N₂ and CO₂ are explained on page 6.
2. Elements and compounds (Table 3.1)
| Kind of substance | What it is made of | Examples |
|---|---|---|
| Element മൂലകം | Only one kind of atom. Its formula has only one symbol. | Potassium K, oxygen O₂, nitrogen N₂, helium He, hydrogen H₂ |
| Compound സംയുക്തം | Two or more different elements chemically joined in a fixed ratio. Its formula has two or more different symbols. | Water H₂O, common salt NaCl, sugar C₁₂H₂₂O₁₁, methane CH₄ |
Activity (pages 43–44). ചില പദാർഥങ്ങൾ ചുവടെ നൽകിയിരിക്കുന്നു. അവയെ മൂലകങ്ങൾ, സംയുക്തങ്ങൾ എന്നിങ്ങനെ വേർതിരിച്ച് പട്ടികപ്പെടുത്തുക. പൊട്ടാസ്യം, ഓക്സിജൻ, ജലം, കറിയുപ്പ്, നൈട്രജൻ, ഹീലിയം, ഹൈഡ്രജൻ, പഞ്ചസാര Some substances are given below. Sort them into elements and compounds and tabulate them (Table 3.1): potassium, oxygen, water, common salt, nitrogen, helium, hydrogen, sugar.
| Element മൂലകം | Compound സംയുക്തം |
|---|---|
| potassium (K) | water (H₂O) |
| oxygen (O₂) | common salt (NaCl) |
| nitrogen (N₂) | sugar (C₁₂H₂₂O₁₁) |
| helium (He) | |
| hydrogen (H₂) |
3. Reading a chemical formula
A chemical formula (രാസസൂത്രം) tells you which atoms are in one molecule and how many of each. Learn these four reading rules:
- Each symbol stands for one atom of that element. A symbol starts with a capital letter: in NaCl, Na and Cl are the two symbols.
- A small number written low on the right is a subscript (പാദാങ്കം). It tells how many atoms of the symbol just before it. H₂O = 2 H + 1 O. No subscript means 1.
- A subscript after a bracket multiplies everything inside the bracket. Ca(OH)₂ = 1 Ca + 2 O + 2 H. (You will write formulas like this on page 10.)
- A big number in front counts molecules. 2H₂O means two water molecules: 4 H + 2 O = 6 atoms.
Type ordinary digits for subscripts (H2O). Capital letters matter: Co is cobalt, but CO is carbon + oxygen. Only elements 1–36 and a few common heavier ones are known to the reader.
Activity (page 44). ഹൈഡ്രജന്റെ ഒരു തന്മാത്രയിൽ രണ്ട് ആറ്റങ്ങളാണുള്ളതെന്ന് നിങ്ങൾക്കറിയാമല്ലോ. അങ്ങനെയെങ്കിൽ താഴെ കൊടുത്തിട്ടുള്ള പദാർഥങ്ങളുടെ ഓരോ തന്മാത്രയിലും എത്ര ആറ്റങ്ങൾ വീതമുണ്ട്? You know that a molecule of hydrogen has two atoms. Then how many atoms are there in one molecule of each substance below? Fill in Table 3.2.
ചില തന്മാത്രകളിൽ ഒന്നിൽക്കൂടുതൽ ആറ്റങ്ങൾ ഉണ്ടെന്ന് പട്ടിക 3.2-ൽ നിന്നും മനസ്സിലാക്കാൻ കഴിഞ്ഞല്ലോ. – Table 3.2 shows that many molecules have more than one atom. Helium is the odd one: its molecule is a single atom.
4. One, two or many atoms
| Kind of molecule | Atoms in one molecule | Examples |
|---|---|---|
| Monatomic | 1 | The noble gases: helium He, neon Ne, argon Ar (ഉൽകൃഷ്ട വാതകങ്ങൾ, page 3 tells you why) |
| Diatomic ദ്വയാറ്റോമിക തന്മാത്ര | 2 | Elements: H₂, N₂, O₂, F₂, Cl₂ (and Br₂, I₂). Compounds: HCl, HF, CO |
| Polyatomic | 3 or more | H₂O (3), CO₂ (3), NH₃ (4), CH₄ (5), ozone O₃ (3), sugar C₁₂H₂₂O₁₁ (45) |
Not really. Solid common salt is a huge crystal of charged particles called ions, packed in the ratio 1 sodium : 1 chlorine. The formula NaCl gives that ratio, not a small separate molecule. You will see why on pages 4–5.
Think. Oxygen gas O₂ and ozone O₃ are both made of only oxygen atoms. Are they elements or compounds?
5. Metals and non-metals
When atoms bond, it matters a great deal whether they are metals (ലോഹങ്ങൾ) or non-metals (അലോഹങ്ങൾ). Metals are shiny, malleable and conduct electricity: sodium, magnesium, aluminium, potassium, calcium, iron, copper. Non-metals are usually dull, brittle and do not conduct: hydrogen, carbon, nitrogen, oxygen, fluorine, sulphur, chlorine. Boron and silicon are metalloids (ഉപലോഹങ്ങൾ), with both natures.
A preview of the big idea: a metal + a non-metal usually join by giving and taking electrons (an ionic bond, pages 4–5). Non-metal + non-metal usually join by sharing electrons (a covalent bond, pages 6–7). Noble gases usually do not join at all (page 3).
- The force of attraction (ആകർഷണബലം) between constituent particles (ഘടക കണങ്ങൾ) holds a substance together.
- An element (മൂലകം) has one kind of atom; a compound (സംയുക്തം) has different elements joined in a fixed ratio.
- In a formula, a subscript (പാദാങ്കം) counts the atoms of the symbol just before it; a subscript after a bracket multiplies everything inside; a number in front counts molecules.
- Noble gases are monatomic; H₂, N₂, O₂, F₂, Cl₂ are diatomic (ദ്വയാറ്റോമിക തന്മാത്ര); H₂O, CH₄ and sugar are polyatomic.
- Metal + non-metal → usually electron transfer; non-metal + non-metal → usually sharing.