Chemistry Basics for RRB NTPC: Matter, Atoms, Acids and Everyday Compounds
A from-scratch, Class 10 level guide to the chemistry that RRB NTPC loves to ask: what matter is, what an atom is made of, how acids, bases and salts behave, and how metals, non-metals and common compounds differ — explained in simple English with a worked example and quick-revision tables.
By the PadhoDost Team · 📖 7 min read · Updated 4 August 2026
Part of Railway Exams (RRB) prep🧠 Your kitchen is a chemistry lab
Look around an Indian kitchen. The steel vessel is a metal, the namak in the dabba is a compound (sodium chloride), the nimbu you squeeze is an acid, and the baking soda for your pakoras is a base. Everything you can touch, pour or smell is 'matter', and all of it is built from tiny atoms. Chemistry is simply the story of what these atoms are and how they join up. Once you see it this way, this whole chapter starts to feel familiar. Padho, dost!
Matter: what everything is made of
Matter is anything that has mass and takes up space (occupies volume). Your notebook, the air you breathe, the water in your bottle — all are matter. At the Class 10 level we study three states of matter: solid, liquid and gas. The real difference between them comes down to how tightly the tiny particles are packed together and how freely those particles can move.
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed | Takes shape of container | Fills the whole container |
| Volume | Fixed | Fixed | Not fixed |
| Compressibility | Almost none | Very little | High |
| Particle movement | Vibrate in place | Slide past each other | Move freely and fast |
| Example | Ice | Water | Steam (water vapour) |
Inside the atom
Every piece of matter is built from tiny units called atoms. An atom has a dense centre called the nucleus, which holds positively charged protons and neutral neutrons. Negatively charged electrons move around the nucleus. A proton and a neutron have almost the same mass (about 1 unit each), while an electron is nearly 1836 times lighter, so almost all the mass of an atom sits in its nucleus. Because an atom has equal numbers of protons and electrons, it stays electrically neutral overall. (For your notes: the electron was discovered by J.J. Thomson and the neutron by James Chadwick.)
📝 Counting the particles in a sodium (Na) atom
Given: atomic number (Z) = 11, mass number (A) = 23
Number of protons = Z = 11
Number of electrons = number of protons (neutral atom) = 11
Number of neutrons = A − Z = 23 − 11 = 12
So a sodium atom has 11 protons, 11 electrons and 12 neutrons
Acids, bases and salts
Acids and bases are two opposite families of compounds. An acid releases hydrogen ions (H+) when dissolved in water, tastes sour (think lemon or imli) and turns blue litmus paper red. A base releases hydroxide ions (OH−) in water, tastes bitter, feels soapy and turns red litmus paper blue. We measure how acidic or basic a solution is on the pH scale, which runs from 0 to 14, with 7 being neutral. When an acid reacts with a base, they cancel each other out in a neutralisation reaction, producing a salt and water (for example, HCl + NaOH gives NaCl + water).
| Feature | Acid | Base |
|---|---|---|
| Taste | Sour | Bitter |
| Litmus test | Turns blue litmus red | Turns red litmus blue |
| pH value | Less than 7 | More than 7 |
| Ion released in water | H+ (hydrogen ion) | OH− (hydroxide ion) |
| Examples | HCl, H2SO4, citric acid | NaOH, Ca(OH)2 |
Metals, non-metals and everyday compounds
| Property | Metals | Non-metals |
|---|---|---|
| Appearance | Shiny (lustrous) | Dull (except iodine, graphite) |
| Malleable / ductile | Yes | No — mostly brittle |
| Conductivity | Good conductors | Poor (except graphite) |
| State at room temperature | Solid (except mercury, a liquid) | Solid, liquid or gas |
| Nature of their oxide | Basic | Acidic |
| Examples | Iron, copper, gold | Oxygen, sulphur, carbon |
Everyday compounds worth memorising
- ✓Common salt = sodium chloride = NaCl (cooking, food preservation)
- ✓Baking soda = sodium hydrogen carbonate = NaHCO3 (a mild base, used in cooking and antacids)
- ✓Washing soda = sodium carbonate = Na2CO3·10H2O (cleaning, softening hard water)
- ✓Slaked lime = calcium hydroxide = Ca(OH)2 (whitewashing walls)
- ✓Quick lime = calcium oxide = CaO; limestone / marble / chalk = calcium carbonate = CaCO3
- ✓Plaster of Paris = CaSO4·½H2O (used to support fractured bones)
⚡ Quick check
An aluminium atom has atomic number 13 and mass number 27. How many neutrons does it have?
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